Threads: task pointer stored in ngx_file_t. This simplifies the interface of the ngx_thread_read() function. Additionally, most of the thread operations now explicitly set file->thread_task, file->thread_handler and file->thread_ctx, to facilitate use of thread operations in other places. (Potential problems remain with sendfile in threads though - it uses file->thread_handler as set in ngx_output_chain(), and it should not be overwritten to an incompatible one.) In collaboration with Valentin Bartenev.

--- a/src/core/ngx_file.h
+++ b/src/core/ngx_file.h
@@ -27,6 +27,7 @@ struct ngx_file_s {
     ngx_int_t                (*thread_handler)(ngx_thread_task_t *task,
                                                ngx_file_t *file);
     void                      *thread_ctx;
+    ngx_thread_task_t         *thread_task;
 #endif
 
 #if (NGX_HAVE_FILE_AIO)