Changed ngx_chain_update_chains() to test tag first (ticket #2248). Without this change, aio used with HTTP/2 can result in connection hang, as observed with "aio threads; aio_write on;" and proxying (ticket #2248). The problem is that HTTP/2 updates buffers outside of the output filters (notably, marks them as sent), and then posts a write event to call output filters. If a filter does not call the next one for some reason (for example, because of an AIO operation in progress), this might result in a state when the owner of a buffer already called ngx_chain_update_chains() and can reuse the buffer, while the same buffer is still sitting in the busy chain of some other filter. In the particular case a buffer was sitting in output chain's ctx->busy, and was reused by event pipe. Output chain's ctx->busy was permanently blocked by it, and this resulted in connection hang. Fix is to change ngx_chain_update_chains() to skip buffers from other modules unconditionally, without trying to wait for these buffers to become empty.

/*
 * Copyright (C) Nginx, Inc.
 * Copyright (C) Valentin V. Bartenev
 */


#ifndef _NGX_THREAD_POOL_H_INCLUDED_
#define _NGX_THREAD_POOL_H_INCLUDED_


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


struct ngx_thread_task_s {
    ngx_thread_task_t   *next;
    ngx_uint_t           id;
    void                *ctx;
    void               (*handler)(void *data, ngx_log_t *log);
    ngx_event_t          event;
};


typedef struct ngx_thread_pool_s  ngx_thread_pool_t;


ngx_thread_pool_t *ngx_thread_pool_add(ngx_conf_t *cf, ngx_str_t *name);
ngx_thread_pool_t *ngx_thread_pool_get(ngx_cycle_t *cycle, ngx_str_t *name);

ngx_thread_task_t *ngx_thread_task_alloc(ngx_pool_t *pool, size_t size);
ngx_int_t ngx_thread_task_post(ngx_thread_pool_t *tp, ngx_thread_task_t *task);


#endif /* _NGX_THREAD_POOL_H_INCLUDED_ */