Mercurial > hg > nginx-site
annotate xml/en/docs/dev/development_guide.xml @ 1907:42ed974b83a5
Fixed the duplicated reference in development guide.
The ngx_handle_read_event() is mentioned twice, where ngx_handle_write_event()
is supposed to be.
author | Vladimir Homutov <vl@nginx.com> |
---|---|
date | Mon, 13 Feb 2017 19:36:18 +0300 |
parents | 862e96a39fe3 |
children | f8659301a260 |
rev | line source |
---|---|
1899 | 1 <?xml version="1.0"?> |
2 | |
3 <!-- | |
4 Copyright (C) Nginx, Inc. | |
5 --> | |
6 | |
7 <!DOCTYPE article SYSTEM "../../../../dtd/article.dtd"> | |
8 | |
9 <article name="Development guide" | |
10 link="/en/docs/dev/development_guide.html" | |
11 lang="en" | |
12 rev="1"> | |
13 | |
14 <section name="Introduction" id="introduction"> | |
15 | |
16 | |
17 <section name="Code layout" id="code_layout"> | |
18 | |
19 <para> | |
20 <list type="bullet"> | |
21 <listitem> | |
22 <literal>auto</literal> - build scripts | |
23 </listitem> | |
24 | |
25 <listitem> | |
26 <literal>src</literal> | |
27 | |
28 <list type="bullet"> | |
29 | |
30 <listitem> | |
31 <literal>core</literal> - basic types and functions - string, array, log, | |
32 pool etc | |
33 </listitem> | |
34 | |
35 <listitem> | |
36 <literal>event</literal> - event core | |
37 | |
38 <list type="bullet"> | |
39 | |
40 <listitem> | |
41 <literal>modules</literal> - event notification modules: epoll, kqueue, | |
42 select etc | |
43 </listitem> | |
44 | |
45 </list> | |
46 | |
47 </listitem> | |
48 | |
49 <listitem> | |
50 <literal>http</literal> - core HTTP module and common code | |
51 | |
52 <list type="bullet"> | |
53 | |
54 <listitem> | |
55 <literal>modules</literal> - other HTTP modules | |
56 </listitem> | |
57 | |
58 <listitem> | |
59 <literal>v2</literal> - HTTPv2 | |
60 </listitem> | |
61 | |
62 </list> | |
63 | |
64 </listitem> | |
65 | |
66 <listitem> | |
67 <literal>mail</literal> - mail modules | |
68 </listitem> | |
69 | |
70 <listitem> | |
71 <literal>os</literal> - platform-specific code | |
72 | |
73 <list type="bullet"> | |
74 | |
75 <listitem> | |
76 <literal>unix</literal> | |
77 </listitem> | |
78 | |
79 <listitem> | |
80 <literal>win32</literal> | |
81 </listitem> | |
82 | |
83 </list> | |
84 | |
85 </listitem> | |
86 | |
87 <listitem> | |
88 <literal>stream</literal> - stream modules | |
89 </listitem> | |
90 | |
91 </list> | |
92 | |
93 </listitem> | |
94 | |
95 </list> | |
96 </para> | |
97 | |
98 </section> | |
99 | |
100 | |
101 <section name="Include files" id="include_files"> | |
102 | |
103 <para> | |
104 Each nginx file should start with including the following two files: | |
105 </para> | |
106 | |
107 | |
108 <programlisting> | |
109 #include <ngx_config.h> | |
110 #include <ngx_core.h> | |
111 </programlisting> | |
112 | |
113 <para> | |
114 In addition to that, HTTP code should include | |
115 </para> | |
116 | |
117 | |
118 <programlisting> | |
119 #include <ngx_http.h> | |
120 </programlisting> | |
121 | |
122 <para> | |
123 Mail code should include | |
124 </para> | |
125 | |
126 | |
127 <programlisting> | |
128 #include <ngx_mail.h> | |
129 </programlisting> | |
130 | |
131 <para> | |
132 Stream code should include | |
133 </para> | |
134 | |
135 | |
136 <programlisting> | |
137 #include <ngx_stream.h> | |
138 </programlisting> | |
139 | |
140 </section> | |
141 | |
142 | |
143 <section name="Integers" id="integers"> | |
144 | |
145 <para> | |
146 For general purpose, nginx code uses the following two integer types | |
147 <literal>ngx_int_t</literal> and <literal>ngx_uint_t</literal> which are | |
148 typedefs for <literal>intptr_t</literal> and <literal>uintptr_t</literal>. | |
149 </para> | |
150 | |
151 </section> | |
152 | |
153 | |
154 <section name="Common return codes" id="common_return_codes"> | |
155 | |
156 <para> | |
157 Most functions in nginx return the following codes: | |
158 </para> | |
159 | |
160 <para> | |
161 <list type="bullet"> | |
162 | |
163 <listitem> | |
164 <literal>NGX_OK</literal> - operation succeeded | |
165 </listitem> | |
166 | |
167 <listitem> | |
168 <literal>NGX_ERROR</literal> - operation failed | |
169 </listitem> | |
170 | |
171 <listitem> | |
172 <literal>NGX_AGAIN</literal> - operation incomplete, function should be called | |
173 again | |
174 </listitem> | |
175 | |
176 <listitem> | |
177 <literal>NGX_DECLINED</literal> - operation rejected, for example, if disabled | |
178 in configuration. This is never an error | |
179 </listitem> | |
180 | |
181 <listitem> | |
182 <literal>NGX_BUSY</literal> - resource is not available | |
183 </listitem> | |
184 | |
185 <listitem> | |
186 <literal>NGX_DONE</literal> - operation done or continued elsewhere. | |
187 Also used as an alternative success code | |
188 </listitem> | |
189 | |
190 <listitem> | |
191 <literal>NGX_ABORT</literal> - function was aborted. | |
192 Also used as an alternative error code | |
193 </listitem> | |
194 | |
195 </list> | |
196 </para> | |
197 | |
198 </section> | |
199 | |
200 | |
201 <section name="Error handling" id="error_handling"> | |
202 | |
203 <para> | |
204 For getting the last system error code, the <literal>ngx_errno</literal> macro | |
205 is available. | |
206 It's mapped to <literal>errno</literal> on POSIX platforms and to | |
207 <literal>GetLastError()</literal> call in Windows. | |
208 For getting the last socket error number, the | |
209 <literal>ngx_socket_errno</literal> macro is available. | |
210 It's mapped to <literal>errno</literal> on POSIX systems as well, | |
211 and to <literal>WSAGetLastError()</literal> call on Windows. | |
212 For performance reasons the values of <literal>ngx_errno</literal> or | |
213 <literal>ngx_socket_errno</literal> should not be accessed more than | |
214 once in a row. | |
215 The error value should be stored in a local variable of type | |
216 <literal>ngx_err_t</literal> for using multiple times, if required. | |
217 For setting errors, <literal>ngx_set_errno(errno)</literal> and | |
218 <literal>ngx_set_socket_errno(errno)</literal> macros are available. | |
219 </para> | |
220 | |
221 <para> | |
222 The values of <literal>ngx_errno</literal> or | |
223 <literal>ngx_socket_errno</literal> can be passed to logging functions | |
224 <literal>ngx_log_error()</literal> and <literal>ngx_log_debugX()</literal>, in | |
225 which case system error text is added to the log message. | |
226 </para> | |
227 | |
228 <para> | |
229 Example using <literal>ngx_errno</literal>: | |
230 </para> | |
231 | |
232 | |
233 <programlisting> | |
234 void | |
235 ngx_my_kill(ngx_pid_t pid, ngx_log_t *log, int signo) | |
236 { | |
237 ngx_err_t err; | |
238 | |
239 if (kill(pid, signo) == -1) { | |
240 err = ngx_errno; | |
241 | |
242 ngx_log_error(NGX_LOG_ALERT, log, err, "kill(%P, %d) failed", pid, signo); | |
243 | |
244 if (err == NGX_ESRCH) { | |
245 return 2; | |
246 } | |
247 | |
248 return 1; | |
249 } | |
250 | |
251 return 0; | |
252 } | |
253 </programlisting> | |
254 | |
255 </section> | |
256 | |
257 | |
258 </section> | |
259 | |
260 | |
261 <section name="Strings" id="strings"> | |
262 | |
263 | |
264 <section name="Overview" id="overview"> | |
265 | |
266 <para> | |
267 For C strings, nginx code uses unsigned character type pointer | |
268 <literal>u_char *</literal>. | |
269 </para> | |
270 | |
271 <para> | |
272 The nginx string type <literal>ngx_str_t</literal> is defined as follows: | |
273 </para> | |
274 | |
275 | |
276 <programlisting> | |
277 typedef struct { | |
278 size_t len; | |
279 u_char *data; | |
280 } ngx_str_t; | |
281 </programlisting> | |
282 | |
283 <para> | |
284 The <literal>len</literal> field holds the string length, | |
285 <literal>data</literal> holds the string data. | |
286 The string, held in <literal>ngx_str_t</literal>, may or may not be | |
287 null-terminated after the <literal>len</literal> bytes. | |
288 In most cases it’s not. | |
289 However, in certain parts of code (for example, when parsing configuration), | |
290 <literal>ngx_str_t</literal> objects are known to be null-terminated, and that | |
291 knowledge is used to simplify string comparison and makes it easier to pass | |
292 those strings to syscalls. | |
293 </para> | |
294 | |
295 <para> | |
296 A number of string operations are provided in nginx. | |
297 They are declared in <literal>src/core/ngx_string.h</literal>. | |
298 Some of them are wrappers around standard C functions: | |
299 </para> | |
300 | |
301 <para> | |
302 <list type="bullet"> | |
303 | |
304 <listitem> | |
305 <literal>ngx_strcmp()</literal> | |
306 </listitem> | |
307 | |
308 <listitem> | |
309 <literal>ngx_strncmp()</literal> | |
310 </listitem> | |
311 | |
312 <listitem> | |
313 <literal>ngx_strstr()</literal> | |
314 </listitem> | |
315 | |
316 <listitem> | |
317 <literal>ngx_strlen()</literal> | |
318 </listitem> | |
319 | |
320 <listitem> | |
321 <literal>ngx_strchr()</literal> | |
322 </listitem> | |
323 | |
324 <listitem> | |
325 <literal>ngx_memcmp()</literal> | |
326 </listitem> | |
327 | |
328 <listitem> | |
329 <literal>ngx_memset()</literal> | |
330 </listitem> | |
331 | |
332 <listitem> | |
333 <literal>ngx_memcpy()</literal> | |
334 </listitem> | |
335 | |
336 <listitem> | |
337 <literal>ngx_memmove()</literal> | |
338 </listitem> | |
339 | |
340 </list> | |
341 | |
342 </para> | |
343 | |
344 <para> | |
345 Some nginx-specific string functions: | |
346 </para> | |
347 | |
348 <para> | |
349 <list type="bullet"> | |
350 | |
351 <listitem> | |
352 <literal>ngx_memzero()</literal> fills memory with zeroes | |
353 </listitem> | |
354 | |
355 <listitem> | |
356 <literal>ngx_cpymem()</literal> does the same as | |
357 <literal>ngx_memcpy()</literal>, but returns the final destination address | |
358 This one is handy for appending multiple strings in a row | |
359 </listitem> | |
360 | |
361 <listitem> | |
362 <literal>ngx_movemem()</literal> does the same as | |
363 <literal>ngx_memmove()</literal>, but returns the final destination address. | |
364 </listitem> | |
365 | |
366 <listitem> | |
367 <literal>ngx_strlchr()</literal> searches for a character in a string, | |
368 delimited by two pointers | |
369 </listitem> | |
370 </list> | |
371 </para> | |
372 | |
373 <para> | |
374 Some case conversion and comparison functions: | |
375 </para> | |
376 | |
377 <para> | |
378 <list type="bullet"> | |
379 | |
380 <listitem> | |
381 <literal>ngx_tolower()</literal> | |
382 </listitem> | |
383 | |
384 <listitem> | |
385 <literal>ngx_toupper()</literal> | |
386 </listitem> | |
387 | |
388 <listitem> | |
389 <literal>ngx_strlow()</literal> | |
390 </listitem> | |
391 | |
392 <listitem> | |
393 <literal>ngx_strcasecmp()</literal> | |
394 </listitem> | |
395 | |
396 <listitem> | |
397 <literal>ngx_strncasecmp()</literal> | |
398 </listitem> | |
399 | |
400 </list> | |
401 </para> | |
402 | |
403 </section> | |
404 | |
405 | |
406 <section name="Formatting" id="formatting"> | |
407 | |
408 <para> | |
409 A number of formatting functions are provided by nginx. These functions support nginx-specific types: | |
410 </para> | |
411 | |
412 | |
413 <para> | |
414 <list type="bullet"> | |
415 | |
416 <listitem> | |
417 <literal>ngx_sprintf(buf, fmt, ...)</literal> | |
418 </listitem> | |
419 | |
420 <listitem> | |
421 <literal>ngx_snprintf(buf, max, fmt, ...)</literal> | |
422 </listitem> | |
423 | |
424 <listitem> | |
425 <literal>ngx_slrintf(buf, last, fmt, ...)</literal> | |
426 </listitem> | |
427 | |
428 <listitem> | |
429 <literal>ngx_vslprint(buf, last, fmt, args)</literal> | |
430 </listitem> | |
431 | |
432 <listitem> | |
433 <literal>ngx_vsnprint(buf, max, fmt, args)</literal> | |
434 </listitem> | |
435 | |
436 </list> | |
437 </para> | |
438 | |
439 <para> | |
440 The full list of formatting options, supported by these functions, can be found | |
441 in <literal>src/core/ngx_string.c</literal>. Some of them are: | |
442 </para> | |
443 | |
444 | |
445 <programlisting> | |
446 %O - off_t | |
447 %T - time_t | |
448 %z - size_t | |
449 %i - ngx_int_t | |
450 %p - void * | |
451 %V - ngx_str_t * | |
452 %s - u_char * (null-terminated) | |
453 %*s - size_t + u_char * | |
454 </programlisting> | |
455 | |
456 <para> | |
457 The ‘u’ modifier makes most types unsigned, ‘X’/‘x’ convert output to hex. | |
458 </para> | |
459 | |
460 <para> | |
461 Example: | |
462 | |
463 <programlisting> | |
464 u_char buf[NGX_INT_T_LEN]; | |
465 size_t len; | |
466 ngx_int_t n; | |
467 | |
468 /* set n here */ | |
469 | |
470 len = ngx_sprintf(buf, "%ui", n) - buf; | |
471 </programlisting> | |
472 | |
473 </para> | |
474 | |
475 </section> | |
476 | |
477 | |
478 <section name="Numeric conversion" id="numeric_conversion"> | |
479 | |
480 <para> | |
481 Several functions for numeric conversion are implemented in nginx: | |
482 </para> | |
483 | |
484 <para> | |
485 <list type="bullet"> | |
486 | |
487 <listitem> | |
488 <literal>ngx_atoi(line, n)</literal> - converts a string of given length to a | |
489 positive integer of type <literal>ngx_int_t</literal>. | |
490 Returns <literal>NGX_ERROR</literal> on error | |
491 </listitem> | |
492 | |
493 <listitem> | |
494 <literal>ngx_atosz(line, n)</literal> - same for <literal>ssize_t</literal> | |
495 type | |
496 </listitem> | |
497 | |
498 <listitem> | |
499 <literal>ngx_atoof(line, n)</literal> - same for <literal>off_t</literal> | |
500 type | |
501 </listitem> | |
502 | |
503 <listitem> | |
504 <literal>ngx_atotm(line, n)</literal> - same for <literal>time_t</literal> | |
505 type | |
506 </listitem> | |
507 | |
508 <listitem> | |
509 <literal>ngx_atofp(line, n, point)</literal> - converts a fixed point floating | |
510 number of given length to a positive integer of type | |
511 <literal>ngx_int_t</literal>. | |
512 The result is shifted left by <literal>points</literal> decimal | |
513 positions. The string representation of the number is expected to have no more | |
514 than <literal>points</literal> fractional digits. | |
515 Returns <literal>NGX_ERROR</literal> on error. For example, | |
516 <literal>ngx_atofp("10.5", 4, 2)</literal> returns <literal>1050</literal> | |
517 </listitem> | |
518 | |
519 <listitem> | |
520 <literal>ngx_hextoi(line, n)</literal> - converts hexadecimal representation of | |
521 a positive integer to <literal>ngx_int_t</literal>. Returns | |
522 <literal>NGX_ERROR</literal> on error | |
523 </listitem> | |
524 | |
525 </list> | |
526 </para> | |
527 | |
528 </section> | |
529 | |
530 | |
531 </section> | |
532 | |
533 | |
534 <section name="Containers" id="containers"> | |
535 | |
536 | |
537 <section name="Array" id="array"> | |
538 | |
539 <para> | |
540 The nginx array type <literal>ngx_array_t</literal> is defined as follows | |
541 </para> | |
542 | |
543 | |
544 <programlisting> | |
545 typedef struct { | |
546 void *elts; | |
547 ngx_uint_t nelts; | |
548 size_t size; | |
549 ngx_uint_t nalloc; | |
550 ngx_pool_t *pool; | |
551 } ngx_array_t; | |
552 </programlisting> | |
553 | |
554 <para> | |
555 The elements of array are available through the <literal>elts</literal> field. | |
556 The number of elements is held in the <literal>nelts</literal> field. | |
557 The <literal>size</literal> field holds the size of a single element and is set | |
558 when initializing the array. | |
559 </para> | |
560 | |
561 <para> | |
562 An array can be created in a pool with the | |
563 <literal>ngx_array_create(pool, n, size)</literal> call. | |
564 An already allocated array object can be initialized with the | |
565 <literal>ngx_array_init(array, pool, n, size)</literal> call. | |
566 </para> | |
567 | |
568 | |
569 <programlisting> | |
570 ngx_array_t *a, b; | |
571 | |
572 /* create an array of strings with preallocated memory for 10 elements */ | |
573 a = ngx_array_create(pool, 10, sizeof(ngx_str_t)); | |
574 | |
575 /* initialize string array for 10 elements */ | |
576 ngx_array_init(&b, pool, 10, sizeof(ngx_str_t)); | |
577 </programlisting> | |
578 | |
579 <para> | |
580 Adding elements to array are done with the following functions: | |
581 </para> | |
582 | |
583 <para> | |
584 <list type="bullet"> | |
585 | |
586 <listitem> | |
587 <literal>ngx_array_push(a)</literal> adds one tail element and returns pointer | |
588 to it | |
589 </listitem> | |
590 | |
591 <listitem> | |
592 <literal>ngx_array_push_n(a, n)</literal> adds <literal>n</literal> tail elements | |
593 and returns pointer to the first one | |
594 </listitem> | |
595 | |
596 </list> | |
597 </para> | |
598 | |
599 <para> | |
600 If currently allocated memory is not enough for new elements, a new memory for | |
601 elements is allocated and existing elements are copied to that memory. | |
602 The new memory block is normally twice as large, as the existing one. | |
603 </para> | |
604 | |
605 | |
606 <programlisting> | |
607 s = ngx_array_push(a); | |
608 ss = ngx_array_push_n(&b, 3); | |
609 </programlisting> | |
610 | |
611 </section> | |
612 | |
613 | |
614 <section name="List" id="list"> | |
615 | |
616 <para> | |
617 List in nginx is a sequence of arrays, optimized for inserting a potentially | |
618 large number of items. The list type is defined as follows: | |
619 </para> | |
620 | |
621 | |
622 <programlisting> | |
623 typedef struct { | |
624 ngx_list_part_t *last; | |
625 ngx_list_part_t part; | |
626 size_t size; | |
627 ngx_uint_t nalloc; | |
628 ngx_pool_t *pool; | |
629 } ngx_list_t; | |
630 </programlisting> | |
631 | |
632 <para> | |
633 The actual items are store in list parts, defined as follows: | |
634 </para> | |
635 | |
636 | |
637 <programlisting> | |
638 typedef struct ngx_list_part_s ngx_list_part_t; | |
639 | |
640 struct ngx_list_part_s { | |
641 void *elts; | |
642 ngx_uint_t nelts; | |
643 ngx_list_part_t *next; | |
644 }; | |
645 </programlisting> | |
646 | |
647 <para> | |
648 Initially, a list must be initialized by calling | |
649 <literal>ngx_list_init(list, pool, n, size)</literal> or created by calling | |
650 <literal>ngx_list_create(pool, n, size)</literal>. | |
651 Both functions receive the size of a single item and a number of items per list | |
652 part. | |
653 The <literal>ngx_list_push(list)</literal> function is used to add an item to the | |
654 list. Iterating over the items is done by direct accessing the list fields, as | |
655 seen in the example: | |
656 </para> | |
657 | |
658 | |
659 <programlisting> | |
660 ngx_str_t *v; | |
661 ngx_uint_t i; | |
662 ngx_list_t *list; | |
663 ngx_list_part_t *part; | |
664 | |
665 list = ngx_list_create(pool, 100, sizeof(ngx_str_t)); | |
666 if (list == NULL) { /* error */ } | |
667 | |
668 /* add items to the list */ | |
669 | |
670 v = ngx_list_push(list); | |
671 if (v == NULL) { /* error */ } | |
672 ngx_str_set(v, “foo”); | |
673 | |
674 v = ngx_list_push(list); | |
675 if (v == NULL) { /* error */ } | |
676 ngx_str_set(v, “bar”); | |
677 | |
678 /* iterate over the list */ | |
679 | |
680 part = &list->part; | |
681 v = part->elts; | |
682 | |
683 for (i = 0; /* void */; i++) { | |
684 | |
685 if (i >= part->nelts) { | |
686 if (part->next == NULL) { | |
687 break; | |
688 } | |
689 | |
690 part = part->next; | |
691 v = part->elts; | |
692 i = 0; | |
693 } | |
694 | |
695 ngx_do_smth(&v[i]); | |
696 } | |
697 </programlisting> | |
698 | |
699 <para> | |
700 The primary use for the list in nginx is HTTP input and output headers. | |
701 </para> | |
702 | |
703 <para> | |
704 The list does not support item removal. | |
705 However, when needed, items can internally be marked as missing without actual | |
706 removing from the list. | |
707 For example, HTTP output headers which are stored as | |
708 <literal>ngx_table_elt_t</literal> objects, are marked as missing by setting | |
709 the <literal>hash</literal> field of <literal>ngx_table_elt_t</literal> to | |
710 zero. Such items are explicitly skipped, when iterating over the headers. | |
711 </para> | |
712 | |
713 </section> | |
714 | |
715 | |
716 <section name="Queue" id="queue"> | |
717 | |
718 <para> | |
719 Queue in nginx is an intrusive doubly linked list, with each node defined as | |
720 follows: | |
721 </para> | |
722 | |
723 | |
724 <programlisting> | |
725 typedef struct ngx_queue_s ngx_queue_t; | |
726 | |
727 struct ngx_queue_s { | |
728 ngx_queue_t *prev; | |
729 ngx_queue_t *next; | |
730 }; | |
731 </programlisting> | |
732 | |
733 <para> | |
734 The head queue node is not linked with any data. Before using, the list head | |
735 should be initialized with <literal>ngx_queue_init(q)</literal> call. | |
736 Queues support the following operations: | |
737 </para> | |
738 | |
739 <para> | |
740 <list type="bullet"> | |
741 | |
742 <listitem> | |
743 <literal>ngx_queue_insert_head(h, x)</literal>, | |
744 <literal>ngx_queue_insert_tail(h, x)</literal> - insert a new node | |
745 </listitem> | |
746 | |
747 <listitem> | |
748 <literal>ngx_queue_remove(x)</literal> - remove a queue node | |
749 </listitem> | |
750 | |
751 <listitem> | |
752 <literal>ngx_queue_split(h, q, n)</literal> - split a queue at a node, | |
753 queue tail is returned in a separate queue | |
754 </listitem> | |
755 | |
756 <listitem> | |
757 <literal>ngx_queue_add(h, n)</literal> - add second queue to the first queue | |
758 </listitem> | |
759 | |
760 <listitem> | |
761 <literal>ngx_queue_head(h)</literal>, | |
762 <literal>ngx_queue_last(h)</literal> - get first or last queue node | |
763 </listitem> | |
764 | |
765 <listitem> | |
766 <literal>ngx_queue_sentinel(h)</literal> | |
767 - get a queue sentinel object to end iteration at | |
768 </listitem> | |
769 | |
770 <listitem> | |
771 <literal>ngx_queue_data(q, type, link)</literal> - get reference to the beginning of a | |
772 queue node data structure, considering the queue field offset in it | |
773 </listitem> | |
774 | |
775 </list> | |
776 </para> | |
777 | |
778 <para> | |
779 Example: | |
780 </para> | |
781 | |
782 | |
783 <programlisting> | |
784 typedef struct { | |
785 ngx_str_t value; | |
786 ngx_queue_t queue; | |
787 } ngx_foo_t; | |
788 | |
789 ngx_foo_t *f; | |
790 ngx_queue_t values; | |
791 | |
792 ngx_queue_init(&values); | |
793 | |
794 f = ngx_palloc(pool, sizeof(ngx_foo_t)); | |
795 if (f == NULL) { /* error */ } | |
796 ngx_str_set(&f->value, “foo”); | |
797 | |
798 ngx_queue_insert_tail(&values, f); | |
799 | |
800 /* insert more nodes here */ | |
801 | |
802 for (q = ngx_queue_head(&values); | |
803 q != ngx_queue_sentinel(&values); | |
804 q = ngx_queue_next(q)) | |
805 { | |
806 f = ngx_queue_data(q, ngx_foo_t, queue); | |
807 | |
808 ngx_do_smth(&f->value); | |
809 } | |
810 </programlisting> | |
811 | |
812 </section> | |
813 | |
814 | |
815 <section name="Red-Black tree" id="red_black_tree"> | |
816 | |
817 <para> | |
818 The <literal>src/core/ngx_rbtree.h</literal> header file provides access to the | |
819 effective implementation of red-black trees. | |
820 </para> | |
821 | |
822 | |
823 <programlisting> | |
824 typedef struct { | |
825 ngx_rbtree_t rbtree; | |
826 ngx_rbtree_node_t sentinel; | |
827 | |
828 /* custom per-tree data here */ | |
829 } my_tree_t; | |
830 | |
831 typedef struct { | |
832 ngx_rbtree_node_t rbnode; | |
833 | |
834 /* custom per-node data */ | |
835 foo_t val; | |
836 } my_node_t; | |
837 </programlisting> | |
838 | |
839 <para> | |
840 To deal with a tree as a whole, you need two nodes: root and sentinel. | |
841 Typically, they are added to some custom structure, thus allowing to | |
842 organize your data into a tree which leaves contain a link to or embed | |
843 your data. | |
844 </para> | |
845 | |
846 <para> | |
847 To initialize a tree: | |
848 </para> | |
849 | |
850 | |
851 <programlisting> | |
852 my_tree_t root; | |
853 | |
854 ngx_rbtree_init(&root.rbtree, &root.sentinel, insert_value_function); | |
855 </programlisting> | |
856 | |
857 <para> | |
858 The <literal>insert_value_function</literal> is a function that is | |
859 responsible for traversing the tree and inserting new values into correct | |
860 place. | |
861 For example, the <literal>ngx_str_rbtree_insert_value</literal> functions is | |
862 designed to deal with <literal>ngx_str_t</literal> type. | |
863 </para> | |
864 | |
865 | |
866 <programlisting> | |
867 void ngx_str_rbtree_insert_value(ngx_rbtree_node_t *temp, | |
868 ngx_rbtree_node_t *node, | |
869 ngx_rbtree_node_t *sentinel) | |
870 </programlisting> | |
871 | |
872 <para> | |
873 Its arguments are pointers to a root node of an insertion, newly created node | |
874 to be added, and a tree sentinel. | |
875 </para> | |
876 | |
877 <para> | |
878 The traversal is pretty straightforward and can be demonstrated with the | |
879 following lookup function pattern: | |
880 </para> | |
881 | |
882 | |
883 <programlisting> | |
884 my_node_t * | |
885 my_rbtree_lookup(ngx_rbtree_t *rbtree, foo_t *val, uint32_t hash) | |
886 { | |
887 ngx_int_t rc; | |
888 my_node_t *n; | |
889 ngx_rbtree_node_t *node, *sentinel; | |
890 | |
891 node = rbtree->root; | |
892 sentinel = rbtree->sentinel; | |
893 | |
894 while (node != sentinel) { | |
895 | |
896 n = (my_node_t *) node; | |
897 | |
898 if (hash != node->key) { | |
899 node = (hash < node->key) ? node->left : node->right; | |
900 continue; | |
901 } | |
902 | |
903 rc = compare(val, node->val); | |
904 | |
905 if (rc < 0) { | |
906 node = node->left; | |
907 continue; | |
908 } | |
909 | |
910 if (rc > 0) { | |
911 node = node->right; | |
912 continue; | |
913 } | |
914 | |
915 return n; | |
916 } | |
917 | |
918 return NULL; | |
919 } | |
920 </programlisting> | |
921 | |
922 <para> | |
923 The <literal>compare()</literal> is a classic comparator function returning | |
924 value less, equal or greater than zero. To speed up lookups and avoid comparing | |
925 user objects that can be big, integer hash field is used. | |
926 </para> | |
927 | |
928 <para> | |
929 To add a node to a tree, allocate a new node, initialize it and call | |
930 <literal>ngx_rbtree_insert()</literal>: | |
931 </para> | |
932 | |
933 | |
934 <programlisting> | |
935 my_node_t *my_node; | |
936 ngx_rbtree_node_t *node; | |
937 | |
938 my_node = ngx_palloc(...); | |
939 init_custom_data(&my_node->val); | |
940 | |
941 node = &my_node->rbnode; | |
942 node->key = create_key(my_node->val); | |
943 | |
944 ngx_rbtree_insert(&root->rbtree, node); | |
945 </programlisting> | |
946 | |
947 <para> | |
948 to remove a node: | |
949 </para> | |
950 | |
951 | |
952 <programlisting> | |
953 ngx_rbtree_delete(&root->rbtree, node); | |
954 </programlisting> | |
955 | |
956 </section> | |
957 | |
958 | |
959 </section> | |
960 | |
961 | |
962 <section name="Memory management" id="memory_management"> | |
963 | |
964 | |
965 <section name="Heap" id="heap"> | |
966 | |
967 <para> | |
968 To allocate memory from system heap, the following functions are provided by | |
969 nginx: | |
970 </para> | |
971 | |
972 <para> | |
973 <list type="bullet"> | |
974 | |
975 <listitem> | |
976 <literal>ngx_alloc(size, log)</literal> - allocate memory from system heap. | |
977 This is a wrapper around <literal>malloc()</literal> with logging support. | |
978 Allocation error and debugging information is logged to <literal>log</literal> | |
979 </listitem> | |
980 | |
981 <listitem> | |
982 <literal>ngx_calloc(size, log)</literal> - same as | |
983 <literal>ngx_alloc()</literal>, but memory is filled with zeroes after | |
984 allocation | |
985 </listitem> | |
986 | |
987 <listitem> | |
988 <literal>ngx_memalign(alignment, size, log)</literal> - allocate aligned memory | |
989 from system heap. This is a wrapper around <literal>posix_memalign()</literal> | |
990 on those platforms which provide it. | |
991 Otherwise implementation falls back to <literal>ngx_alloc()</literal> which | |
992 provides maximum alignment | |
993 </listitem> | |
994 | |
995 <listitem> | |
996 <literal>ngx_free(p)</literal> - free allocated memory. | |
997 This is a wrapper around <literal>free()</literal> | |
998 </listitem> | |
999 | |
1000 </list> | |
1001 </para> | |
1002 | |
1003 </section> | |
1004 | |
1005 | |
1006 <section name="Pool" id="pool"> | |
1007 | |
1008 <para> | |
1009 Most nginx allocations are done in pools. Memory allocated in an nginx pool is | |
1010 freed automatically when the pool in destroyed. This provides good | |
1011 allocation performance and makes memory control easy. | |
1012 </para> | |
1013 | |
1014 <para> | |
1015 A pool internally allocates objects in continuous blocks of memory. Once a | |
1016 block is full, a new one is allocated and added to the pool memory | |
1017 block list. When a large allocation is requested which does not fit into | |
1018 a block, such allocation is forwarded to the system allocator and the | |
1019 returned pointer is stored in the pool for further deallocation. | |
1020 </para> | |
1021 | |
1022 <para> | |
1023 Nginx pool has the type <literal>ngx_pool_t</literal>. | |
1024 The following operations are supported: | |
1025 </para> | |
1026 | |
1027 <para> | |
1028 <list type="bullet"> | |
1029 | |
1030 <listitem> | |
1031 <literal>ngx_create_pool(size, log)</literal> - create a pool with given | |
1032 block size. The pool object returned is allocated in the pool as well. | |
1033 </listitem> | |
1034 | |
1035 <listitem> | |
1036 <literal>ngx_destroy_pool(pool)</literal> - free all pool memory, including | |
1037 the pool object itself. | |
1038 </listitem> | |
1039 | |
1040 <listitem> | |
1041 <literal>ngx_palloc(pool, size)</literal> - allocate aligned memory from pool | |
1042 </listitem> | |
1043 | |
1044 <listitem> | |
1045 <literal>ngx_pcalloc(pool, size)</literal> - allocated aligned memory | |
1046 from pool and fill it with zeroes | |
1047 </listitem> | |
1048 | |
1049 <listitem> | |
1050 <literal>ngx_pnalloc(pool, size)</literal> - allocate unaligned memory from pool. | |
1051 Mostly used for allocating strings | |
1052 </listitem> | |
1053 | |
1054 <listitem> | |
1055 <literal>ngx_pfree(pool, p)</literal> - free memory, previously allocated | |
1056 in the pool. | |
1057 Only allocations, forwarded to the system allocator, can be freed. | |
1058 </listitem> | |
1059 | |
1060 </list> | |
1061 </para> | |
1062 | |
1063 <programlisting> | |
1064 u_char *p; | |
1065 ngx_str_t *s; | |
1066 ngx_pool_t *pool; | |
1067 | |
1068 pool = ngx_create_pool(1024, log); | |
1069 if (pool == NULL) { /* error */ } | |
1070 | |
1071 s = ngx_palloc(pool, sizeof(ngx_str_t)); | |
1072 if (s == NULL) { /* error */ } | |
1073 ngx_str_set(s, “foo”); | |
1074 | |
1075 p = ngx_pnalloc(pool, 3); | |
1076 if (p == NULL) { /* error */ } | |
1077 ngx_memcpy(p, “foo”, 3); | |
1078 </programlisting> | |
1079 | |
1080 <para> | |
1081 Since chain links <literal>ngx_chain_t</literal> are actively used in nginx, | |
1082 nginx pool provides a way to reuse them. | |
1083 The <literal>chain</literal> field of <literal>ngx_pool_t</literal> keeps a | |
1084 list of previously allocated links ready for reuse. For efficient allocation of | |
1085 a chain link in a pool, the function | |
1086 <literal>ngx_alloc_chain_link(pool)</literal> should be used. | |
1087 This function looks up a free chain link in the pool list and only if it's | |
1088 empty allocates a new one. To free a link <literal>ngx_free_chain(pool, cl)</literal> | |
1089 should be called. | |
1090 </para> | |
1091 | |
1092 <para> | |
1093 Cleanup handlers can be registered in a pool. | |
1094 Cleanup handler is a callback with an argument which is called when pool is | |
1095 destroyed. | |
1096 Pool is usually tied with a specific nginx object (like HTTP request) and | |
1097 destroyed in the end of that object’s lifetime, releasing the object itself. | |
1902 | 1098 Registering a pool cleanup is a convenient way to release resources, close file |
1899 | 1099 descriptors or make final adjustments to shared data, associated with the main |
1100 object. | |
1101 </para> | |
1102 | |
1103 <para> | |
1104 A pool cleanup is registered by calling <literal>ngx_pool_cleanup_add(pool, | |
1105 size)</literal> which returns <literal>ngx_pool_cleanup_t</literal> pointer to | |
1106 be filled by the caller. The <literal>size</literal> argument allows allocating | |
1107 context for the cleanup handler. | |
1108 </para> | |
1109 | |
1110 | |
1111 <programlisting> | |
1112 ngx_pool_cleanup_t *cln; | |
1113 | |
1114 cln = ngx_pool_cleanup_add(pool, 0); | |
1115 if (cln == NULL) { /* error */ } | |
1116 | |
1117 cln->handler = ngx_my_cleanup; | |
1118 cln->data = “foo”; | |
1119 | |
1120 ... | |
1121 | |
1122 static void | |
1123 ngx_my_cleanup(void *data) | |
1124 { | |
1125 u_char *msg = data; | |
1126 | |
1127 ngx_do_smth(msg); | |
1128 } | |
1129 </programlisting> | |
1130 | |
1131 </section> | |
1132 | |
1133 | |
1134 <section name="Shared memory" id="shared_memory"> | |
1135 | |
1136 <para> | |
1137 Shared memory is used by nginx to share common data between processes. | |
1138 Function <literal>ngx_shared_memory_add(cf, name, size, tag)</literal> adds a | |
1139 new shared memory entry <literal>ngx_shm_zone_t</literal> to the cycle. The | |
1140 function receives <literal>name</literal> and <literal>size</literal> of the | |
1141 zone. | |
1142 Each shared zone must have a unique name. | |
1143 If a shared zone entry with the provided name exists, the old zone entry is | |
1144 reused, if its tag value matches too. | |
1145 Mismatched tag is considered an error. | |
1146 Usually, the address of the module structure is passed as tag, making it | |
1147 possible to reuse shared zones by name within one nginx module. | |
1148 </para> | |
1149 | |
1150 <para> | |
1151 The shared memory entry structure <literal>ngx_shm_zone_t</literal> has the | |
1152 following fields: | |
1153 </para> | |
1154 | |
1155 <para> | |
1156 <list type="bullet"> | |
1157 | |
1158 <listitem> | |
1159 <literal>init</literal> - initialization callback, called after shared zone is | |
1160 mapped to actual memory | |
1161 </listitem> | |
1162 | |
1163 <listitem> | |
1164 <literal>data</literal> - data context, used to pass arbitrary data to the | |
1165 <literal>init</literal> callback | |
1166 </listitem> | |
1167 | |
1168 <listitem> | |
1169 <literal>noreuse</literal> - flag, disabling shared zone reuse from the | |
1170 old cycle | |
1171 </listitem> | |
1172 | |
1173 <listitem> | |
1174 <literal>tag</literal> - shared zone tag | |
1175 </listitem> | |
1176 | |
1177 <listitem> | |
1178 <literal>shm</literal> - platform-specific object of type | |
1179 <literal>ngx_shm_t</literal>, having at least the following fields: | |
1180 <list type="bullet"> | |
1181 | |
1182 <listitem> | |
1183 <literal>addr</literal> - mapped shared memory address, initially NULL | |
1184 </listitem> | |
1185 | |
1186 <listitem> | |
1187 <literal>size</literal> - shared memory size | |
1188 </listitem> | |
1189 | |
1190 <listitem> | |
1191 <literal>name</literal> - shared memory name | |
1192 </listitem> | |
1193 | |
1194 <listitem> | |
1195 <literal>log</literal> - shared memory log | |
1196 </listitem> | |
1197 | |
1198 <listitem> | |
1199 <literal>exists</literal> - flag, showing that shared memory was inherited | |
1200 from the master process (Windows-specific) | |
1201 </listitem> | |
1202 | |
1203 </list> | |
1204 </listitem> | |
1205 | |
1206 </list> | |
1207 </para> | |
1208 | |
1209 <para> | |
1210 Shared zone entries are mapped to actual memory in | |
1211 <literal>ngx_init_cycle()</literal> after configuration is parsed. | |
1212 On POSIX systems, <literal>mmap()</literal> syscall is used to create shared | |
1213 anonymous mapping. | |
1214 On Windows, <literal>CreateFileMapping()/MapViewOfFileEx()</literal> pair is | |
1215 used. | |
1216 </para> | |
1217 | |
1218 <para> | |
1219 For allocating in shared memory, nginx provides slab pool | |
1220 <literal>ngx_slab_pool_t</literal>. | |
1221 In each nginx shared zone, a slab pool is automatically created for allocating | |
1222 memory in that zone. | |
1223 The pool is located in the beginning of the shared zone and can be accessed by | |
1224 the expression <literal>(ngx_slab_pool_t *) shm_zone->shm.addr</literal>. | |
1225 Allocation in shared zone is done by calling one of the functions | |
1226 <literal>ngx_slab_alloc(pool, size)/ngx_slab_calloc(pool, size)</literal>. | |
1227 Memory is freed by calling <literal>ngx_slab_free(pool, p)</literal>. | |
1228 </para> | |
1229 | |
1230 <para> | |
1231 Slab pool divides all shared zone into pages. | |
1232 Each page is used for allocating objects of the same size. | |
1233 Only the sizes which are powers of 2, and not less than 8, are considered. | |
1234 Other sizes are rounded up to one of these values. | |
1235 For each page, a bitmask is kept, showing which blocks within that page are in | |
1236 use and which are free for allocation. | |
1237 For sizes greater than half-page (usually, 2048 bytes), allocation is done by | |
1238 entire pages. | |
1239 </para> | |
1240 | |
1241 <para> | |
1242 To protect data in shared memory from concurrent access, mutex is available in | |
1243 the <literal>mutex</literal> field of <literal>ngx_slab_pool_t</literal>. | |
1244 The mutex is used by the slab pool while allocating and freeing memory. | |
1245 However, it can be used to protect any other user data structures, | |
1246 allocated in the shared zone. | |
1247 Locking is done by calling | |
1248 <literal>ngx_shmtx_lock(&shpool->mutex)</literal>, unlocking is done by | |
1249 calling <literal>ngx_shmtx_unlock(&shpool->mutex)</literal>. | |
1250 </para> | |
1251 | |
1252 | |
1253 <programlisting> | |
1254 ngx_str_t name; | |
1255 ngx_foo_ctx_t *ctx; | |
1256 ngx_shm_zone_t *shm_zone; | |
1257 | |
1258 ngx_str_set(&name, "foo"); | |
1259 | |
1260 /* allocate shared zone context */ | |
1261 ctx = ngx_pcalloc(cf->pool, sizeof(ngx_foo_ctx_t)); | |
1262 if (ctx == NULL) { | |
1263 /* error */ | |
1264 } | |
1265 | |
1266 /* add an entry for 65k shared zone */ | |
1267 shm_zone = ngx_shared_memory_add(cf, &name, 65536, &ngx_foo_module); | |
1268 if (shm_zone == NULL) { | |
1269 /* error */ | |
1270 } | |
1271 | |
1272 /* register init callback and context */ | |
1273 shm_zone->init = ngx_foo_init_zone; | |
1274 shm_zone->data = ctx; | |
1275 | |
1276 | |
1277 ... | |
1278 | |
1279 | |
1280 static ngx_int_t | |
1281 ngx_foo_init_zone(ngx_shm_zone_t *shm_zone, void *data) | |
1282 { | |
1283 ngx_foo_ctx_t *octx = data; | |
1284 | |
1285 size_t len; | |
1286 ngx_foo_ctx_t *ctx; | |
1287 ngx_slab_pool_t *shpool; | |
1288 | |
1289 value = shm_zone->data; | |
1290 | |
1291 if (octx) { | |
1292 /* reusing a shared zone from old cycle */ | |
1293 ctx->value = octx->value; | |
1294 return NGX_OK; | |
1295 } | |
1296 | |
1297 shpool = (ngx_slab_pool_t *) shm_zone->shm.addr; | |
1298 | |
1299 if (shm_zone->shm.exists) { | |
1300 /* initialize shared zone context in Windows nginx worker */ | |
1301 ctx->value = shpool->data; | |
1302 return NGX_OK; | |
1303 } | |
1304 | |
1305 /* initialize shared zone */ | |
1306 | |
1307 ctx->value = ngx_slab_alloc(shpool, sizeof(ngx_uint_t)); | |
1308 if (ctx->value == NULL) { | |
1309 return NGX_ERROR; | |
1310 } | |
1311 | |
1312 shpool->data = ctx->value; | |
1313 | |
1314 return NGX_OK; | |
1315 } | |
1316 </programlisting> | |
1317 | |
1318 </section> | |
1319 | |
1320 | |
1321 </section> | |
1322 | |
1323 | |
1324 <section name="Logging" id="logging"> | |
1325 | |
1326 <para> | |
1327 For logging nginx code uses <literal>ngx_log_t</literal> objects. | |
1328 Nginx logger provides support for several types of output: | |
1329 | |
1330 <list type="bullet"> | |
1331 | |
1332 <listitem> | |
1333 stderr - logging to standard error output | |
1334 </listitem> | |
1335 | |
1336 <listitem> | |
1337 file - logging to file | |
1338 </listitem> | |
1339 | |
1340 <listitem> | |
1341 syslog - logging to syslog | |
1342 </listitem> | |
1343 | |
1344 <listitem> | |
1345 memory - logging to internal memory storage for development purposes. | |
1346 The memory could be accessed later with debugger | |
1347 </listitem> | |
1348 | |
1349 </list> | |
1350 </para> | |
1351 | |
1352 <para> | |
1353 A logger instance may actually be a chain of loggers, linked to each other with | |
1354 the <literal>next</literal> field. | |
1355 Each message is written to all loggers in chain. | |
1356 </para> | |
1357 | |
1358 <para> | |
1359 Each logger has an error level which limits the messages written to that log. | |
1360 The following error levels are supported by nginx: | |
1361 </para> | |
1362 | |
1363 <para> | |
1364 <list type="bullet"> | |
1365 | |
1366 <listitem> | |
1367 <literal>NGX_LOG_EMERG</literal> | |
1368 </listitem> | |
1369 | |
1370 <listitem> | |
1371 <literal>NGX_LOG_ALERT</literal> | |
1372 </listitem> | |
1373 | |
1374 <listitem> | |
1375 <literal>NGX_LOG_CRIT</literal> | |
1376 </listitem> | |
1377 | |
1378 <listitem> | |
1379 <literal>NGX_LOG_ERR</literal> | |
1380 </listitem> | |
1381 | |
1382 <listitem> | |
1383 <literal>NGX_LOG_WARN</literal> | |
1384 </listitem> | |
1385 | |
1386 <listitem> | |
1387 <literal>NGX_LOG_NOTICE</literal> | |
1388 </listitem> | |
1389 | |
1390 <listitem> | |
1391 <literal>NGX_LOG_INFO</literal> | |
1392 </listitem> | |
1393 | |
1394 <listitem> | |
1395 <literal>NGX_LOG_DEBUG</literal> | |
1396 </listitem> | |
1397 | |
1398 </list> | |
1399 </para> | |
1400 | |
1401 <para> | |
1402 For debug logging, debug mask is checked as well. The following debug masks | |
1403 exist: | |
1404 </para> | |
1405 | |
1406 <para> | |
1407 <list type="bullet"> | |
1408 | |
1409 <listitem> | |
1410 <literal>NGX_LOG_DEBUG_CORE</literal> | |
1411 </listitem> | |
1412 | |
1413 <listitem> | |
1414 <literal>NGX_LOG_DEBUG_ALLOC</literal> | |
1415 </listitem> | |
1416 | |
1417 <listitem> | |
1418 <literal>NGX_LOG_DEBUG_MUTEX</literal> | |
1419 </listitem> | |
1420 | |
1421 <listitem> | |
1422 <literal>NGX_LOG_DEBUG_EVENT</literal> | |
1423 </listitem> | |
1424 | |
1425 <listitem> | |
1426 <literal>NGX_LOG_DEBUG_HTTP</literal> | |
1427 </listitem> | |
1428 | |
1429 <listitem> | |
1430 <literal>NGX_LOG_DEBUG_MAIL</literal> | |
1431 </listitem> | |
1432 | |
1433 <listitem> | |
1434 <literal>NGX_LOG_DEBUG_STREAM</literal> | |
1435 </listitem> | |
1436 | |
1437 </list> | |
1438 </para> | |
1439 | |
1440 <para> | |
1441 Normally, loggers are created by existing nginx code from | |
1442 <literal>error_log</literal> directives and are available at nearly every stage | |
1443 of processing in cycle, configuration, client connection and other objects. | |
1444 </para> | |
1445 | |
1446 <para> | |
1447 Nginx provides the following logging macros: | |
1448 </para> | |
1449 | |
1450 <para> | |
1451 <list type="bullet"> | |
1452 | |
1453 <listitem> | |
1454 <literal>ngx_log_error(level, log, err, fmt, ...)</literal> - error logging | |
1455 </listitem> | |
1456 | |
1457 <listitem> | |
1458 <literal>ngx_log_debug0(level, log, err, fmt)</literal>, | |
1459 <literal>ngx_log_debug1(level, log, err, fmt, arg1)</literal> etc - debug | |
1460 logging, up to 8 formatting arguments are supported | |
1461 </listitem> | |
1462 | |
1463 </list> | |
1464 </para> | |
1465 | |
1466 <para> | |
1467 A log message is formatted in a buffer of size | |
1468 <literal>NGX_MAX_ERROR_STR</literal> (currently, 2048 bytes) on stack. | |
1469 The message is prepended with error level, process PID, connection id (stored | |
1470 in <literal>log->connection</literal>) and system error text. | |
1471 For non-debug messages <literal>log->handler</literal> is called as well to | |
1472 prepend more specific information to the log message. | |
1473 HTTP module sets <literal>ngx_http_log_error()</literal> function as log | |
1474 handler to log client and server addresses, current action (stored in | |
1475 <literal>log->action</literal>), client request line, server name etc. | |
1476 </para> | |
1477 | |
1478 <para> | |
1479 Example: | |
1480 </para> | |
1481 | |
1482 | |
1483 <programlisting> | |
1484 /* specify what is currently done */ | |
1485 log->action = "sending mp4 to client”; | |
1486 | |
1487 /* error and debug log */ | |
1488 ngx_log_error(NGX_LOG_INFO, c->log, 0, "client prematurely | |
1489 closed connection”); | |
1490 | |
1491 ngx_log_debug2(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0, | |
1492 "mp4 start:%ui, length:%ui”, mp4->start, mp4->length); | |
1493 </programlisting> | |
1494 | |
1495 <para> | |
1496 Logging result: | |
1497 </para> | |
1498 | |
1499 | |
1500 <programlisting> | |
1501 2016/09/16 22:08:52 [info] 17445#0: *1 client prematurely closed connection while | |
1502 sending mp4 to client, client: 127.0.0.1, server: , request: "GET /file.mp4 HTTP/1.1” | |
1503 2016/09/16 23:28:33 [debug] 22140#0: *1 mp4 start:0, length:10000 | |
1504 </programlisting> | |
1505 | |
1506 </section> | |
1507 | |
1508 | |
1509 <section name="Cycle" id="cycle"> | |
1510 | |
1511 <para> | |
1512 Cycle object keeps nginx runtime context, created from a specific | |
1513 configuration. | |
1514 The type of the cycle is <literal>ngx_cycle_t</literal>. | |
1515 Upon configuration reload a new cycle is created from the new version of nginx | |
1516 configuration. | |
1517 The old cycle is usually deleted after a new one is successfully created. | |
1518 Currently active cycle is held in the <literal>ngx_cycle</literal> global | |
1519 variable and is inherited by newly started nginx workers. | |
1520 </para> | |
1521 | |
1522 <para> | |
1523 A cycle is created by the function <literal>ngx_init_cycle()</literal>. | |
1524 The function receives the old cycle as the argument. | |
1525 It's used to locate the configuration file and inherit as much resources as | |
1526 possible from the old cycle to keep nginx running smoothly. | |
1527 When nginx starts, a fake cycle called "init cycle" is created and is then | |
1528 replaced by a normal cycle, built from configuration. | |
1529 </para> | |
1530 | |
1531 <para> | |
1532 Some members of the cycle: | |
1533 </para> | |
1534 | |
1535 <para> | |
1536 <list type="bullet"> | |
1537 | |
1538 <listitem> | |
1539 <literal>pool</literal> - cycle pool. Created for each new cycle | |
1540 </listitem> | |
1541 | |
1542 <listitem> | |
1543 <literal>log</literal> - cycle log. Initially, this log is inherited from the | |
1544 old cycle. | |
1545 After reading configuration, this member is set to point to | |
1546 <literal>new_log</literal> | |
1547 </listitem> | |
1548 | |
1549 <listitem> | |
1550 <literal>new_log</literal> - cycle log, created by the configuration. | |
1551 It's affected by the root scope <literal>error_log</literal> directive | |
1552 </listitem> | |
1553 | |
1554 <listitem> | |
1555 <literal>connections</literal>, <literal>connections_n</literal> - per-worker | |
1556 array of connections of type <literal>ngx_connection_t</literal>, created by | |
1557 the event module while initializing each nginx worker. | |
1558 The number of connections is set by the <literal>worker_connections</literal> | |
1559 directive | |
1560 </listitem> | |
1561 | |
1562 <listitem> | |
1563 <literal>free_connections</literal>, | |
1564 <literal>free_connections_n</literal> - the and number of currently available | |
1565 connections. | |
1566 If no connections are available, nginx worker refuses to accept new clients | |
1567 </listitem> | |
1568 | |
1569 <listitem> | |
1570 <literal>files</literal>, <literal>files_n</literal> - array for mapping file | |
1571 descriptors to nginx connections. | |
1572 This mapping is used by the event modules, having the | |
1573 <literal>NGX_USE_FD_EVENT</literal> flag (currently, it's poll and devpoll) | |
1574 </listitem> | |
1575 | |
1576 <listitem> | |
1577 <literal>conf_ctx</literal> - array of core module configurations. | |
1578 The configurations are created and filled while reading nginx configuration | |
1579 files | |
1580 </listitem> | |
1581 | |
1582 <listitem> | |
1583 <literal>modules</literal>, <literal>modules_n</literal> - array of modules | |
1584 <literal>ngx_module_t</literal>, both static and dynamic, loaded by current | |
1585 configuration | |
1586 </listitem> | |
1587 | |
1588 <listitem> | |
1589 <literal>listening</literal> - array of listening objects | |
1590 <literal>ngx_listening_t</literal>. | |
1591 Listening objects are normally added by the the <literal>listen</literal> | |
1592 directive of different modules which call the | |
1593 <literal>ngx_create_listening()</literal> function. | |
1594 Based on listening objects, listen sockets are created by nginx | |
1595 </listitem> | |
1596 | |
1597 <listitem> | |
1598 <literal>paths</literal> - array of paths <literal>ngx_path_t</literal>. | |
1599 Paths are added by calling the function <literal>ngx_add_path()</literal> from | |
1600 modules which are going to operate on certain directories. | |
1601 These directories are created by nginx after reading configuration, if missing. | |
1602 Moreover, two handlers can be added for each path: | |
1603 | |
1604 <list type="bullet"> | |
1605 | |
1606 <listitem> | |
1607 path loader - executed only once in 60 seconds after starting or reloading | |
1608 nginx. Normally, reads the directory and stores data in nginx shared | |
1609 memory. The handler is called from a dedicated nginx process "nginx | |
1610 cache loader" | |
1611 </listitem> | |
1612 | |
1613 <listitem> | |
1614 path manager - executed periodically. Normally, removes old files from the | |
1615 directory and reflects these changes in nginx memory. The handler is | |
1616 called from a dedicated nginx process "nginx cache manager" | |
1617 </listitem> | |
1618 | |
1619 </list> | |
1620 </listitem> | |
1621 | |
1622 <listitem> | |
1623 <literal>open_files</literal> - list of <literal>ngx_open_file_t</literal> | |
1624 objects. | |
1625 An open file object is created by calling the function | |
1626 <literal>ngx_conf_open_file()</literal>. | |
1627 After reading configuration nginx opens all files from the | |
1628 <literal>open_files</literal> list and stores file descriptors in the | |
1629 <literal>fd</literal> field of each open file object. | |
1630 The files are opened in append mode and created if missing. | |
1631 The files from this list are reopened by nginx workers upon receiving the | |
1632 reopen signal (usually it's <literal>USR1</literal>). | |
1633 In this case the <literal>fd</literal> fields are changed to new descriptors. | |
1634 The open files are currently used for logging | |
1635 </listitem> | |
1636 | |
1637 <listitem> | |
1638 <literal>shared_memory</literal> - list of shared memory zones, each added by | |
1639 calling the <literal>ngx_shared_memory_add()</literal> function. | |
1640 Shared zones are mapped to the same address range in all nginx processes and | |
1641 are used to share common data, for example HTTP cache in-memory tree | |
1642 </listitem> | |
1643 | |
1644 </list> | |
1645 </para> | |
1646 | |
1647 </section> | |
1648 | |
1649 <section name="Buffer" id="buffer"> | |
1650 | |
1651 <para> | |
1652 For input/output operations, nginx provides the buffer type | |
1653 <literal>ngx_buf_t</literal>. | |
1654 Normally, it's used to hold data to be written to a destination or read from a | |
1655 source. | |
1656 Buffer can reference data in memory and in file. | |
1657 Technically it's possible that a buffer references both at the same time. | |
1658 Memory for the buffer is allocated separately and is not related to the buffer | |
1659 structure <literal>ngx_buf_t</literal>. | |
1660 </para> | |
1661 | |
1662 <para> | |
1663 The structure <literal>ngx_buf_t</literal> has the following fields: | |
1664 </para> | |
1665 | |
1666 <para> | |
1667 <list type="bullet"> | |
1668 | |
1669 <listitem> | |
1670 <literal>start</literal>, <literal>end</literal> - the boundaries of memory | |
1671 block, allocated for the buffer | |
1672 </listitem> | |
1673 | |
1674 <listitem> | |
1675 <literal>pos</literal>, <literal>last</literal> - memory buffer boundaries, | |
1676 normally a subrange of <literal>start</literal> .. <literal>end</literal> | |
1677 </listitem> | |
1678 | |
1679 <listitem> | |
1680 <literal>file_pos</literal>, <literal>file_last</literal> - file buffer | |
1681 boundaries, these are offsets from the beginning of the file | |
1682 </listitem> | |
1683 | |
1684 <listitem> | |
1685 <literal>tag</literal> - unique value, used to distinguish buffers, created by | |
1686 different nginx module, usually, for the purpose of buffer reuse | |
1687 </listitem> | |
1688 | |
1689 <listitem> | |
1690 <literal>file</literal> - file object | |
1691 </listitem> | |
1692 | |
1693 <listitem> | |
1694 <literal>temporary</literal> - flag, meaning that the buffer references | |
1695 writable memory | |
1696 </listitem> | |
1697 | |
1698 <listitem> | |
1699 <literal>memory</literal> - flag, meaning that the buffer references read-only | |
1700 memory | |
1701 </listitem> | |
1702 | |
1703 <listitem> | |
1704 <literal>in_file</literal> - flag, meaning that current buffer references data | |
1705 in a file | |
1706 </listitem> | |
1707 | |
1708 <listitem> | |
1709 <literal>flush</literal> - flag, meaning that all data prior to this buffer | |
1710 should be flushed | |
1711 </listitem> | |
1712 | |
1713 <listitem> | |
1714 <literal>recycled</literal> - flag, meaning that the buffer can be reused and | |
1715 should be consumed as soon as possible | |
1716 </listitem> | |
1717 | |
1718 <listitem> | |
1719 <literal>sync</literal> - flag, meaning that the buffer carries no data or | |
1720 special signal like <literal>flush</literal> or <literal>last_buf</literal>. | |
1721 Normally, such buffers are considered an error by nginx. This flags allows | |
1722 skipping the error checks | |
1723 </listitem> | |
1724 | |
1725 <listitem> | |
1726 <literal>last_buf</literal> - flag, meaning that current buffer is the last in | |
1727 output | |
1728 </listitem> | |
1729 | |
1730 <listitem> | |
1731 <literal>last_in_chain</literal> - flag, meaning that there's no more data | |
1732 buffers in a (sub)request | |
1733 </listitem> | |
1734 | |
1735 <listitem> | |
1736 <literal>shadow</literal> - reference to another buffer, related to the current | |
1737 buffer. Usually current buffer uses data from the shadow buffer. Once current | |
1738 buffer is consumed, the shadow buffer should normally also be marked as | |
1739 consumed | |
1740 </listitem> | |
1741 | |
1742 <listitem> | |
1743 <literal>last_shadow</literal> - flag, meaning that current buffer is the last | |
1744 buffer, referencing a particular shadow buffer | |
1745 </listitem> | |
1746 | |
1747 <listitem> | |
1748 <literal>temp_file</literal> - flag, meaning that the buffer is in a temporary | |
1749 file | |
1750 </listitem> | |
1751 | |
1752 </list> | |
1753 </para> | |
1754 | |
1755 <para> | |
1756 For input and output buffers are linked in chains. | |
1757 Chain is a sequence of chain links <literal>ngx_chain_t</literal>, defined as | |
1758 follows: | |
1759 </para> | |
1760 | |
1761 | |
1762 <programlisting> | |
1763 typedef struct ngx_chain_s ngx_chain_t; | |
1764 | |
1765 struct ngx_chain_s { | |
1766 ngx_buf_t *buf; | |
1767 ngx_chain_t *next; | |
1768 }; | |
1769 </programlisting> | |
1770 | |
1771 <para> | |
1772 Each chain link keeps a reference to its buffer and a reference to the next | |
1773 chain link. | |
1774 </para> | |
1775 | |
1776 <para> | |
1777 Example of using buffers and chains: | |
1778 </para> | |
1779 | |
1780 | |
1781 <programlisting> | |
1782 ngx_chain_t * | |
1783 ngx_get_my_chain(ngx_pool_t *pool) | |
1784 { | |
1785 ngx_buf_t *b; | |
1786 ngx_chain_t *out, *cl, **ll; | |
1787 | |
1788 /* first buf */ | |
1789 cl = ngx_alloc_chain_link(pool); | |
1790 if (cl == NULL) { /* error */ } | |
1791 | |
1792 b = ngx_calloc_buf(pool); | |
1793 if (b == NULL) { /* error */ } | |
1794 | |
1795 b->start = (u_char *) "foo"; | |
1796 b->pos = b->start; | |
1797 b->end = b->start + 3; | |
1798 b->last = b->end; | |
1799 b->memory = 1; /* read-only memory */ | |
1800 | |
1801 cl->buf = b; | |
1802 out = cl; | |
1803 ll = &cl->next; | |
1804 | |
1805 /* second buf */ | |
1806 cl = ngx_alloc_chain_link(pool); | |
1807 if (cl == NULL) { /* error */ } | |
1808 | |
1809 b = ngx_create_temp_buf(pool, 3); | |
1810 if (b == NULL) { /* error */ } | |
1811 | |
1812 b->last = ngx_cpymem(b->last, "foo", 3); | |
1813 | |
1814 cl->buf = b; | |
1815 cl->next = NULL; | |
1816 *ll = cl; | |
1817 | |
1818 return out; | |
1819 } | |
1820 </programlisting> | |
1821 | |
1822 </section> | |
1823 | |
1824 | |
1825 <section name="Networking" id="networking"> | |
1826 | |
1827 | |
1828 <!-- | |
1829 <section name="Network data types" id="network_data_types"> | |
1830 | |
1831 <para> | |
1832 TBD: ngx_addr_t, ngx_url_t, ngx_socket_t, ngx_sockaddr_t, parse url, parse | |
1833 address... | |
1834 </para> | |
1835 | |
1836 </section> | |
1837 --> | |
1838 | |
1839 <section name="Connection" id="connection"> | |
1840 | |
1841 <para> | |
1842 Connection type <literal>ngx_connection_t</literal> is a wrapper around a | |
1843 socket descriptor. Some of the structure fields are: | |
1844 </para> | |
1845 | |
1846 <para> | |
1847 <list type="bullet"> | |
1848 | |
1849 <listitem> | |
1850 <literal>fd</literal> - socket descriptor | |
1851 </listitem> | |
1852 | |
1853 <listitem> | |
1854 <literal>data</literal> - arbitrary connection context. | |
1855 Normally, a pointer to a higher level object, built on top of the connection, | |
1856 like HTTP request or Stream session | |
1857 </listitem> | |
1858 | |
1859 <listitem> | |
1860 <literal>read</literal>, <literal>write</literal> - read and write events for | |
1861 the connection | |
1862 </listitem> | |
1863 | |
1864 <listitem> | |
1865 <literal>recv</literal>, <literal>send</literal>, | |
1866 <literal>recv_chain</literal>, <literal>send_chain</literal> - I/O operations | |
1867 for the connection | |
1868 </listitem> | |
1869 | |
1870 <listitem> | |
1871 <literal>pool</literal> - connection pool | |
1872 </listitem> | |
1873 | |
1874 <listitem> | |
1875 <literal>log</literal> - connection log | |
1876 </listitem> | |
1877 | |
1878 <listitem> | |
1879 <literal>sockaddr</literal>, <literal>socklen</literal>, | |
1880 <literal>addr_text</literal> - remote socket address in binary and text forms | |
1881 </listitem> | |
1882 | |
1883 <listitem> | |
1884 <literal>local_sockaddr</literal>, <literal>local_socklen</literal> - local | |
1885 socket address in binary form. | |
1886 Initially, these fields are empty. | |
1887 Function <literal>ngx_connection_local_sockaddr()</literal> should be used to | |
1888 get socket local address | |
1889 </listitem> | |
1890 | |
1891 <listitem> | |
1892 <literal>proxy_protocol_addr</literal>, <literal>proxy_protocol_port</literal> | |
1893 - PROXY protocol client address and port, if PROXY protocol is enabled for the | |
1894 connection | |
1895 </listitem> | |
1896 | |
1897 <listitem> | |
1898 <literal>ssl</literal> - nginx connection SSL context | |
1899 </listitem> | |
1900 | |
1901 <listitem> | |
1902 <literal>reusable</literal> - flag, meaning, that the connection is at the | |
1903 state, when it can be reused | |
1904 </listitem> | |
1905 | |
1906 <listitem> | |
1907 <literal>close</literal> - flag, meaning, that the connection is being reused | |
1908 and should be closed | |
1909 </listitem> | |
1910 | |
1911 </list> | |
1912 </para> | |
1913 | |
1914 <para> | |
1915 An nginx connection can transparently encapsulate SSL layer. | |
1916 In this case the connection <literal>ssl</literal> field holds a pointer to an | |
1917 <literal>ngx_ssl_connection_t</literal> structure, keeping all SSL-related data | |
1918 for the connection, including <literal>SSL_CTX</literal> and | |
1919 <literal>SSL</literal>. | |
1920 The handlers <literal>recv</literal>, <literal>send</literal>, | |
1921 <literal>recv_chain</literal>, <literal>send_chain</literal> are set as well to | |
1922 SSL functions. | |
1923 </para> | |
1924 | |
1925 <para> | |
1926 The number of connections per nginx worker is limited by the | |
1927 <literal>worker_connections</literal> value. | |
1928 All connection structures are pre-created when a worker starts and stored in | |
1929 the <literal>connections</literal> field of the cycle object. | |
1930 To reach out for a connection structure, <literal>ngx_get_connection(s, | |
1931 log)</literal> function is used. | |
1932 The function receives a socket descriptor <literal>s</literal> which needs to | |
1933 be wrapped in a connection structure. | |
1934 </para> | |
1935 | |
1936 <para> | |
1937 Since the number of connections per worker is limited, nginx provides a | |
1938 way to grab connections which are currently in use. | |
1939 To enable or disable reuse of a connection, function | |
1940 <literal>ngx_reusable_connection(c, reusable)</literal> is called. | |
1941 Calling <literal>ngx_reusable_connection(c, 1)</literal> sets the | |
1942 <literal>reuse</literal> flag of the connection structure and inserts the | |
1943 connection in the <literal>reusable_connections_queue</literal> of the cycle. | |
1944 Whenever <literal>ngx_get_connection()</literal> finds out there are no | |
1945 available connections in the <literal>free_connections</literal> list of the | |
1946 cycle, it calls <literal>ngx_drain_connections()</literal> to release a | |
1947 specific number of reusable connections. | |
1948 For each such connection, the <literal>close</literal> flag is set and its read | |
1949 handler is called which is supposed to free the connection by calling | |
1950 <literal>ngx_close_connection(c)</literal> and make it available for reuse. | |
1951 To exit the state when a connection can be reused | |
1952 <literal>ngx_reusable_connection(c, 0)</literal> is called. | |
1953 An example of reusable connections in nginx is HTTP client connections which | |
1954 are marked as reusable until some data is received from the client. | |
1955 </para> | |
1956 | |
1957 </section> | |
1958 | |
1959 | |
1960 </section> | |
1961 | |
1962 | |
1963 <section name="Events" id="events"> | |
1964 | |
1965 | |
1966 <section name="Event" id="event"> | |
1967 | |
1968 <para> | |
1969 Event object <literal>ngx_event_t</literal> in nginx provides a way to be | |
1970 notified of a specific event happening. | |
1971 </para> | |
1972 | |
1973 <para> | |
1974 Some of the fields of the <literal>ngx_event_t</literal> are: | |
1975 </para> | |
1976 | |
1977 <para> | |
1978 <list type="bullet"> | |
1979 | |
1980 <listitem> | |
1981 <literal>data</literal> - arbitrary event context, used in event handler, | |
1982 usually, a pointer to a connection, tied with the event | |
1983 </listitem> | |
1984 | |
1985 <listitem> | |
1986 <literal>handler</literal> - callback function to be invoked when the event | |
1987 happens | |
1988 </listitem> | |
1989 | |
1990 <listitem> | |
1991 <literal>write</literal> - flag, meaning that this is the write event. | |
1992 Used to distinguish between read and write events | |
1993 </listitem> | |
1994 | |
1995 <listitem> | |
1996 <literal>active</literal> - flag, meaning that the event is registered for | |
1997 receiving I/O notifications, normally from notification mechanisms like epoll, | |
1998 kqueue, poll | |
1999 </listitem> | |
2000 | |
2001 <listitem> | |
2002 <literal>ready</literal> - flag, meaning that the event has received an | |
2003 I/O notification | |
2004 </listitem> | |
2005 | |
2006 <listitem> | |
2007 <literal>delayed</literal> - flag, meaning that I/O is delayed due to rate | |
2008 limiting | |
2009 </listitem> | |
2010 | |
2011 <listitem> | |
2012 <literal>timer</literal> - Red-Black tree node for inserting the event into | |
2013 the timer tree | |
2014 </listitem> | |
2015 | |
2016 <listitem> | |
2017 <literal>timer_set</literal> - flag, meaning that the event timer is set, | |
2018 but not yet expired | |
2019 </listitem> | |
2020 | |
2021 <listitem> | |
2022 <literal>timedout</literal> - flag, meaning that the event timer has expired | |
2023 </listitem> | |
2024 | |
2025 <listitem> | |
2026 <literal>eof</literal> - read event flag, meaning that the eof has happened | |
2027 while reading data | |
2028 </listitem> | |
2029 | |
2030 <listitem> | |
2031 <literal>pending_eof</literal> - flag, meaning that the eof is pending on the | |
2032 socket, even though there may be some data available before it. | |
2033 The flag is delivered via <literal>EPOLLRDHUP</literal> epoll event or | |
2034 <literal>EV_EOF</literal> kqueue flag | |
2035 </listitem> | |
2036 | |
2037 <listitem> | |
2038 <literal>error</literal> - flag, meaning that an error has happened while | |
2039 reading (for read event) or writing (for write event) | |
2040 </listitem> | |
2041 | |
2042 <listitem> | |
2043 <literal>cancelable</literal> - timer event flag, meaning that the event | |
2044 handler should be called while performing nginx worker graceful shutdown, event | |
2045 though event timeout has not yet expired. The flag provides a way to finalize | |
2046 certain activities, for example, flush log files | |
2047 </listitem> | |
2048 | |
2049 <listitem> | |
2050 <literal>posted</literal> - flag, meaning that the event is posted to queue | |
2051 </listitem> | |
2052 | |
2053 <listitem> | |
2054 <literal>queue</literal> - queue node for posting the event to a queue | |
2055 </listitem> | |
2056 | |
2057 </list> | |
2058 </para> | |
2059 | |
2060 </section> | |
2061 | |
2062 | |
2063 <section name="I/O events" id="i_o_events"> | |
2064 | |
2065 <para> | |
2066 Each connection, received with the | |
2067 <literal>ngx_get_connection()</literal> call, has two events attached to it: | |
2068 <literal>c->read</literal> and <literal>c->write</literal>. | |
2069 These events are used to receive notifications about the socket being ready for | |
2070 reading or writing. | |
2071 All such events operate in Edge-Triggered mode, meaning that they only trigger | |
2072 notifications when the state of the socket changes. | |
2073 For example, doing a partial read on a socket will not make nginx deliver a | |
2074 repeated read notification until more data arrive in the socket. | |
2075 Even when the underlying I/O notification mechanism is essentially | |
2076 Level-Triggered (poll, select etc), nginx will turn the notifications into | |
2077 Edge-Triggered. | |
2078 To make nginx event notifications consistent across all notifications systems | |
2079 on different platforms, it's required, that the functions | |
2080 <literal>ngx_handle_read_event(rev, flags)</literal> and | |
1907
42ed974b83a5
Fixed the duplicated reference in development guide.
Vladimir Homutov <vl@nginx.com>
parents:
1902
diff
changeset
|
2081 <literal>ngx_handle_write_event(wev, lowat)</literal> are called after handling |
1899 | 2082 an I/O socket notification or calling any I/O functions on that socket. |
2083 Normally, these functions are called once in the end of each read or write | |
2084 event handler. | |
2085 </para> | |
2086 | |
2087 </section> | |
2088 | |
2089 | |
2090 <section name="Timer events" id="timer_events"> | |
2091 | |
2092 <para> | |
2093 An event can be set to notify a timeout expiration. | |
2094 The function <literal>ngx_add_timer(ev, timer)</literal> sets a timeout for an | |
2095 event, <literal>ngx_del_timer(ev)</literal> deletes a previously set timeout. | |
2096 Timeouts currently set for all existing events, are kept in a global timeout | |
2097 Red-Black tree <literal>ngx_event_timer_rbtree</literal>. | |
2098 The key in that tree has the type <literal>ngx_msec_t</literal> and is the time | |
2099 in milliseconds since the beginning of January 1, 1970 (modulus | |
2100 <literal>ngx_msec_t</literal> max value) at which the event should expire. | |
2101 The tree structure provides fast inserting and deleting operations, as well as | |
2102 accessing the nearest timeouts. | |
2103 The latter is used by nginx to find out for how long to wait for I/O events | |
2104 and for expiring timeout events afterwards. | |
2105 </para> | |
2106 | |
2107 </section> | |
2108 | |
2109 | |
2110 <section name="Posted events" id="posted_events"> | |
2111 | |
2112 <para> | |
2113 An event can be posted which means that its handler will be called at some | |
2114 point later within the current event loop iteration. | |
2115 Posting events is a good practice for simplifying code and escaping stack | |
2116 overflows. | |
2117 Posted events are held in a post queue. | |
2118 The macro <literal>ngx_post_event(ev, q)</literal> posts the event | |
2119 <literal>ev</literal> to the post queue <literal>q</literal>. | |
2120 Macro <literal>ngx_delete_posted_event(ev)</literal> deletes the event | |
2121 <literal>ev</literal> from whatever queue it's currently posted. | |
2122 Normally, events are posted to the <literal>ngx_posted_events</literal> queue. | |
2123 This queue is processed late in the event loop - after all I/O and timer | |
2124 events are already handled. | |
2125 The function <literal>ngx_event_process_posted()</literal> is called to process | |
2126 an event queue. | |
2127 This function calls event handlers until the queue is not empty. This means | |
2128 that a posted event handler can post more events to be processed within the | |
2129 current event loop iteration. | |
2130 </para> | |
2131 | |
2132 <para> | |
2133 Example: | |
2134 </para> | |
2135 | |
2136 | |
2137 <programlisting> | |
2138 void | |
2139 ngx_my_connection_read(ngx_connection_t *c) | |
2140 { | |
2141 ngx_event_t *rev; | |
2142 | |
2143 rev = c->read; | |
2144 | |
2145 ngx_add_timer(rev, 1000); | |
2146 | |
2147 rev->handler = ngx_my_read_handler; | |
2148 | |
2149 ngx_my_read(rev); | |
2150 } | |
2151 | |
2152 | |
2153 void | |
2154 ngx_my_read_handler(ngx_event_t *rev) | |
2155 { | |
2156 ssize_t n; | |
2157 ngx_connection_t *c; | |
2158 u_char buf[256]; | |
2159 | |
2160 if (rev->timedout) { /* timeout expired */ } | |
2161 | |
2162 c = rev->data; | |
2163 | |
2164 while (rev->ready) { | |
2165 n = c->recv(c, buf, sizeof(buf)); | |
2166 | |
2167 if (n == NGX_AGAIN) { | |
2168 break; | |
2169 } | |
2170 | |
2171 if (n == NGX_ERROR) { /* error */ } | |
2172 | |
2173 /* process buf */ | |
2174 } | |
2175 | |
2176 if (ngx_handle_read_event(rev, 0) != NGX_OK) { /* error */ } | |
2177 } | |
2178 </programlisting> | |
2179 | |
2180 </section> | |
2181 | |
2182 | |
2183 <section name="Event loop" id="event_loop"> | |
2184 | |
2185 <para> | |
2186 All nginx processes which do I/O, have an event loop. | |
2187 The only type of process which does not have I/O, is nginx master process which | |
2188 spends most of its time in <literal>sigsuspend()</literal> call waiting for | |
2189 signals to arrive. | |
2190 Event loop is implemented in <literal>ngx_process_events_and_timers()</literal> | |
2191 function. | |
2192 This function is called repeatedly until the process exits. | |
2193 It has the following stages: | |
2194 </para> | |
2195 | |
2196 <para> | |
2197 <list type="bullet"> | |
2198 | |
2199 <listitem> | |
2200 find nearest timeout by calling <literal>ngx_event_find_timer()</literal>. | |
2201 This function finds the leftmost timer tree node and returns the number of | |
2202 milliseconds until that node expires | |
2203 </listitem> | |
2204 | |
2205 <listitem> | |
2206 process I/O events by calling a handler, specific to event notification | |
2207 mechanism, chosen by nginx configuration. | |
2208 This handler waits for at least one I/O event to happen, but no longer, than | |
2209 the nearest timeout. | |
2210 For each read or write event which has happened, the <literal>ready</literal> | |
2211 flag is set and its handler is called. | |
2212 For Linux, normally, the <literal>ngx_epoll_process_events()</literal> handler | |
2213 is used which calls <literal>epoll_wait()</literal> to wait for I/O events | |
2214 </listitem> | |
2215 | |
2216 <listitem> | |
2217 expire timers by calling <literal>ngx_event_expire_timers()</literal>. | |
2218 The timer tree is iterated from the leftmost element to the right until a not | |
2219 yet expired timeout is found. | |
2220 For each expired node the <literal>timedout</literal> event flag is set, | |
2221 <literal>timer_set</literal> flag is reset, and the event handler is called | |
2222 </listitem> | |
2223 | |
2224 <listitem> | |
2225 process posted events by calling <literal>ngx_event_process_posted()</literal>. | |
2226 The function repeatedly removes the first element from the posted events | |
2227 queue and calls its handler until the queue gets empty | |
2228 </listitem> | |
2229 | |
2230 </list> | |
2231 </para> | |
2232 | |
2233 <para> | |
2234 All nginx processes handle signals as well. | |
2235 Signal handlers only set global variables which are checked after the | |
2236 <literal>ngx_process_events_and_timers()</literal> call. | |
2237 </para> | |
2238 | |
2239 </section> | |
2240 | |
2241 | |
2242 </section> | |
2243 | |
2244 | |
2245 <section name="Processes" id="processes"> | |
2246 | |
2247 <para> | |
2248 There are several types of processes in nginx. | |
2249 The type of current process is kept in the <literal>ngx_process</literal> | |
2250 global variable: | |
2251 </para> | |
2252 | |
2253 <list type="bullet"> | |
2254 | |
2255 <listitem> | |
2256 | |
2257 <para> | |
2258 <literal>NGX_PROCESS_MASTER</literal> - the master process runs the | |
2259 <literal>ngx_master_process_cycle()</literal> function. | |
2260 Master process does not have any I/O and responds only to signals. | |
2261 It reads configuration, creates cycles, starts and controls child processes | |
2262 </para> | |
2263 | |
2264 | |
2265 </listitem> | |
2266 | |
2267 <listitem> | |
2268 | |
2269 <para> | |
2270 <literal>NGX_PROCESS_WORKER</literal> - the worker process runs the | |
2271 <literal>ngx_worker_process_cycle()</literal> function. | |
2272 Worker processes are started by master and handle client connections. | |
2273 They also respond to signals and channel commands, sent from master | |
2274 </para> | |
2275 | |
2276 | |
2277 </listitem> | |
2278 | |
2279 <listitem> | |
2280 | |
2281 <para> | |
2282 <literal>NGX_PROCESS_SINGLE</literal> - single process is the only type | |
2283 of processes which exist in the <literal>master_process off</literal> mode. | |
2284 The cycle function for this process is | |
2285 <literal>ngx_single_process_cycle()</literal>. | |
2286 This process creates cycles and handles client connections | |
2287 </para> | |
2288 | |
2289 | |
2290 </listitem> | |
2291 | |
2292 <listitem> | |
2293 | |
2294 <para> | |
2295 <literal>NGX_PROCESS_HELPER</literal> - currently, there are two types of | |
2296 helper processes: cache manager and cache loader. | |
2297 Both of them share the same cycle function | |
2298 <literal>ngx_cache_manager_process_cycle()</literal>. | |
2299 </para> | |
2300 | |
2301 | |
2302 </listitem> | |
2303 | |
2304 </list> | |
2305 | |
2306 <para> | |
2307 All nginx processes handle the following signals: | |
2308 </para> | |
2309 | |
2310 <list type="bullet"> | |
2311 | |
2312 <listitem> | |
2313 | |
2314 <para> | |
2315 <literal>NGX_SHUTDOWN_SIGNAL</literal> (<literal>SIGQUIT</literal>) - graceful | |
2316 shutdown. | |
2317 Upon receiving this signal master process sends shutdown signal to all child | |
2318 processes. | |
2319 When no child processes are left, master destroys cycle pool and exits. | |
2320 A worker process which received this signal, closes all listening sockets and | |
2321 waits until timeout tree becomes empty, then destroys cycle pool and exits. | |
2322 A cache manager process exits right after receiving this signal. | |
2323 The variable <literal>ngx_quit</literal> is set to one after receiving this | |
2324 signal and immediately reset after being processed. | |
2325 The variable <literal>ngx_exiting</literal> is set to one when worker process | |
2326 is in shutdown state | |
2327 </para> | |
2328 | |
2329 | |
2330 </listitem> | |
2331 | |
2332 <listitem> | |
2333 | |
2334 <para> | |
2335 <literal>NGX_TERMINATE_SIGNAL</literal> (<literal>SIGTERM</literal>) - | |
2336 terminate. | |
2337 Upon receiving this signal master process sends terminate signal to all child | |
2338 processes. | |
2339 If child processes do not exit in 1 second, they are killed with the | |
2340 <literal>SIGKILL</literal> signal. | |
2341 When no child processes are left, master process destroys cycle pool and exits. | |
2342 A worker or cache manager process which received this signal destroys cycle | |
2343 pool and exits. | |
2344 The variable <literal>ngx_terminate</literal> is set to one after receiving | |
2345 this signal | |
2346 </para> | |
2347 | |
2348 | |
2349 </listitem> | |
2350 | |
2351 <listitem> | |
2352 | |
2353 <para> | |
2354 <literal>NGX_NOACCEPT_SIGNAL</literal> (<literal>SIGWINCH</literal>) | |
2355 - gracefully shut down worker processes | |
2356 </para> | |
2357 | |
2358 | |
2359 </listitem> | |
2360 | |
2361 <listitem> | |
2362 | |
2363 <para> | |
2364 <literal>NGX_RECONFIGURE_SIGNAL</literal> (<literal>SIGHUP</literal>) - | |
2365 reconfigure. | |
2366 Upon receiving this signal master process creates a new cycle from | |
2367 configuration file. | |
2368 If the new cycle was created successfully, the old cycle is deleted and new | |
2369 child processes are started. | |
2370 Meanwhile, the old processes receive the shutdown signal. | |
2371 In single-process mode, nginx creates a new cycle as well, but keeps the old | |
2372 one until all clients, tied to the old cycle, are gone. | |
2373 Worker and helper processes ignore this signal | |
2374 </para> | |
2375 | |
2376 | |
2377 </listitem> | |
2378 | |
2379 <listitem> | |
2380 | |
2381 <para> | |
2382 <literal>NGX_REOPEN_SIGNAL</literal> (<literal>SIGUSR1</literal>) - reopen | |
2383 files. | |
2384 Master process passes this signal to workers. | |
2385 Worker processes reopen all <literal>open_files</literal> from the cycle | |
2386 </para> | |
2387 | |
2388 | |
2389 </listitem> | |
2390 | |
2391 <listitem> | |
2392 | |
2393 <para> | |
2394 <literal>NGX_CHANGEBIN_SIGNAL</literal> (<literal>SIGUSR2</literal>) - change | |
2395 nginx binary. | |
2396 Master process starts a new nginx binary and passes there a list of all listen | |
2397 sockets. | |
2398 The list is passed in the environment variable <literal>"NGINX"</literal> in | |
2399 text format, where descriptor numbers separated with semicolons. | |
2400 A new nginx instance reads that variable and adds the sockets to its init | |
2401 cycle. | |
2402 Other processes ignore this signal | |
2403 </para> | |
2404 | |
2405 | |
2406 </listitem> | |
2407 | |
2408 </list> | |
2409 | |
2410 <para> | |
2411 While all nginx worker processes are able to receive and properly handle POSIX | |
2412 signals, master process normally does not pass any signals to workers and | |
2413 helpers with the standard <literal>kill()</literal> syscall. | |
2414 Instead, nginx uses inter-process channels which allow sending messages between | |
2415 all nginx processes. | |
2416 Currently, however, messages are only sent from master to its children. | |
2417 Those messages carry the same signals. | |
2418 The channels are socketpairs with their ends in different processes. | |
2419 </para> | |
2420 | |
2421 <para> | |
2422 When running nginx binary, several values can be specified next to | |
2423 <literal>-s</literal> parameter. | |
2424 Those values are <literal>stop</literal>, <literal>quit</literal>, | |
2425 <literal>reopen</literal>, <literal>reload</literal>. | |
2426 They are converted to signals <literal>NGX_TERMINATE_SIGNAL</literal>, | |
2427 <literal>NGX_SHUTDOWN_SIGNAL</literal>, <literal>NGX_REOPEN_SIGNAL</literal> | |
2428 and <literal>NGX_RECONFIGURE_SIGNAL</literal> and sent to the nginx master | |
2429 process, whose pid is read from nginx pid file. | |
2430 </para> | |
2431 | |
2432 </section> | |
2433 | |
2434 </article> |