Fixed sendfile in threads (or with aio preload) and subrequests. If sendfile in threads is used, it is possible that multiple subrequests will trigger multiple ngx_linux_sendfile_thread() calls, as operations are only serialized in output chain based on r->aio, that is, on subrequest level. This resulted in "task #N already active" alerts, in particular, when running proxy_store.t with "aio threads; sendfile on;". Fix is to tolerate duplicate calls, with an additional safety check that the file is the same as previously used. The same problem also affects "aio on; sendfile on;" on FreeBSD (previously known as "aio sendfile;"), where aio->preload_handler() could be called multiple times due to similar reasons, resulting in "second aio post" alerts. Fix is the same as well. It is also believed that similar problems can arise if a filter calls the next body filter multiple times for some reason. These are mostly theoretical though.

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_CHANNEL_H_INCLUDED_
#define _NGX_CHANNEL_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_event.h>


typedef struct {
     ngx_uint_t  command;
     ngx_pid_t   pid;
     ngx_int_t   slot;
     ngx_fd_t    fd;
} ngx_channel_t;


ngx_int_t ngx_write_channel(ngx_socket_t s, ngx_channel_t *ch, size_t size,
    ngx_log_t *log);
ngx_int_t ngx_read_channel(ngx_socket_t s, ngx_channel_t *ch, size_t size,
    ngx_log_t *log);
ngx_int_t ngx_add_channel_event(ngx_cycle_t *cycle, ngx_fd_t fd,
    ngx_int_t event, ngx_event_handler_pt handler);
void ngx_close_channel(ngx_fd_t *fd, ngx_log_t *log);


#endif /* _NGX_CHANNEL_H_INCLUDED_ */