nginx源码分析线程池详解

Syntax: thread_pool name threads=number [max_queue=number];
Default: thread_pool default threads=32 max_queue=65536;
Context: main

/******************* nginx/src/core/ngx_thread_pool.c ************************/
//创建线程池所需的基础结构
static void * ngx_thread_pool_create_conf(ngx_cycle_t *cycle)
{
  ngx_thread_pool_conf_t *tcf;
   //从cycle->pool指向的内存池中申请一块内存
  tcf = ngx_pcalloc(cycle->pool, sizeof(ngx_thread_pool_conf_t));
  if (tcf == NULL) {
    return NULL;
  }
   
   //先申请包含4个ngx_thread_pool_t指针类型元素的数组
   //ngx_thread_pool_t结构体中保存了一个线程池相关的信息
  if (ngx_array_init(&tcf->pools, cycle->pool, 4,
            sizeof(ngx_thread_pool_t *))
    != NGX_OK)
  {
    return NULL;
  }
 
  return tcf;
}
 
//解析处理配置文件中thread_pool的配置，并将相关信息保存的ngx_thread_pool_t中
static char * ngx_thread_pool(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
  ngx_str_t     *value;
  ngx_uint_t     i;
  ngx_thread_pool_t *tp;
 
  value = cf->args->elts;
 
  //根据thread_pool配置中的name作为线程池的唯一标识（如果重名，只有第一个有效）
  //申请ngx_thread_pool_t结构保存线程池的相关信息
  //由此可见，nginx支持配置多个name不同的线程池
  tp = ngx_thread_pool_add(cf, &value[1]);
  .......
  //处理thread_pool配置行的所有元素
  for (i = 2; i < cf->args->nelts; i++) {
    //检查配置的线程数
    if (ngx_strncmp(value[i].data, "threads=", 8) == 0) {
     .......
    }
     
    //检查配置的最大队列长度
    if (ngx_strncmp(value[i].data, "max_queue=", 10) == 0) {
     .......
    }
  }
  ......
}
 
//判断包含多个线程池的数组中的各个线程池的配置是否正确
static char * ngx_thread_pool_init_conf(ngx_cycle_t *cycle, void *conf)
{
  ....
  ngx_thread_pool_t **tpp;
 
  tpp = tcf->pools.elts;
  //遍历数组中所有的线程池配置，并检查其正确性
  for (i = 0; i < tcf->pools.nelts; i++) {
    .....
  }
 
  return NGX_CONF_OK;
}

/******************* nginx/src/core/ngx_thread_pool.c ************************/
//创建线程池所需的基础结构
static ngx_int_t
ngx_thread_pool_init_worker(ngx_cycle_t *cycle)
{
  ngx_uint_t        i;
  ngx_thread_pool_t    **tpp;
  ngx_thread_pool_conf_t  *tcf;
  //如果不是worker或者只有一个worker就不起用线程池
  if (ngx_process != NGX_PROCESS_WORKER
    && ngx_process != NGX_PROCESS_SINGLE)
  {
    return NGX_OK;
  }
   
  //初始化任务队列
  ngx_thread_pool_queue_init(&ngx_thread_pool_done);
 
  tpp = tcf->pools.elts;
  for (i = 0; i < tcf->pools.nelts; i++) {
    //初始化各个线程池
    if (ngx_thread_pool_init(tpp[i], cycle->log, cycle->pool) != NGX_OK) {
      return NGX_ERROR;
    }
  }
 
  return NGX_OK;
}
 
//线程池初始化
static ngx_int_t ngx_thread_pool_init(ngx_thread_pool_t *tp, ngx_log_t *log, ngx_pool_t *pool)
{
  .....
  //初始化任务队列
  ngx_thread_pool_queue_init(&tp->queue);
 
  //创建线程锁
  if (ngx_thread_mutex_create(&tp->mtx, log) != NGX_OK) {
    return NGX_ERROR;
  }
 
  //创建线程条件变量
  if (ngx_thread_cond_create(&tp->cond, log) != NGX_OK) {
    (void) ngx_thread_mutex_destroy(&tp->mtx, log);
    return NGX_ERROR;
  }
  ......
  for (n = 0; n < tp->threads; n++) {
    //创建线程池中的每个线程
    err = pthread_create(&tid, &attr, ngx_thread_pool_cycle, tp);
    if (err) {
      ngx_log_error(NGX_LOG_ALERT, log, err,
             "pthread_create() failed");
      return NGX_ERROR;
    }
  }
  ......
}
 
//线程池中线程处理主函数
static void *ngx_thread_pool_cycle(void *data)
{
   ......
   for ( ;; ) {
    //阻塞的方式获取线程锁
    if (ngx_thread_mutex_lock(&tp->mtx, tp->log) != NGX_OK) {
      return NULL;
    }
 
    /* the number may become negative */
    tp->waiting--;
 
    //如果任务队列为空，就cond_wait阻塞等待有新任务时调用cond_signal/broadcast触发
    while (tp->queue.first == NULL) {
      if (ngx_thread_cond_wait(&tp->cond, &tp->mtx, tp->log)
        != NGX_OK)
      {
        (void) ngx_thread_mutex_unlock(&tp->mtx, tp->log);
        return NULL;
      }
    }
    //从任务队列中获取task，并将其从队列中移除
    task = tp->queue.first;
    tp->queue.first = task->next;
 
    if (tp->queue.first == NULL) {
      tp->queue.last = &tp->queue.first;
    }
 
    if (ngx_thread_mutex_unlock(&tp->mtx, tp->log) != NGX_OK) {
      return NULL;
    }
    ......
    //task的处理函数
    task->handler(task->ctx, tp->log);
    .....
 
    ngx_spinlock(&ngx_thread_pool_done_lock, 1, 2048);
 
    //将经过预处理的任务添加到done队列中等待调用event的回调函数继续处理
    *ngx_thread_pool_done.last = task;
    ngx_thread_pool_done.last = &task->next;
     
    //防止编译器优化，保证解锁操作是在上述语句执行完毕后再去执行的
    ngx_memory_barrier();
 
    ngx_unlock(&ngx_thread_pool_done_lock);
     
    (void) ngx_notify(ngx_thread_pool_handler);
  }
}
 
//处理pool_done队列上task中包含的每个event事件
static void ngx_thread_pool_handler(ngx_event_t *ev)
{
  .....
  ngx_spinlock(&ngx_thread_pool_done_lock, 1, 2048);
 
  //获取任务链表的头部
  task = ngx_thread_pool_done.first;
  ngx_thread_pool_done.first = NULL;
  ngx_thread_pool_done.last = &ngx_thread_pool_done.first;
 
  ngx_memory_barrier();
 
  ngx_unlock(&ngx_thread_pool_done_lock);
 
  while (task) {
    ngx_log_debug1(NGX_LOG_DEBUG_CORE, ev->log, 0,
            "run completion handler for task #%ui", task->id);
    //遍历队列中的所有任务事件
    event = &task->event;
    task = task->next;
 
    event->complete = 1;
    event->active = 0;
 
    //调用event对应的处理函数有针对性的进行处理
    event->handler(event);
  }
}
 

/*********************** nginx/src/os/unix/ngx_files.c **********************/
//file_cache模块的处理函数（涉及到了线程池）
static ssize_t ngx_http_file_cache_aio_read(ngx_http_request_t *r, ngx_http_cache_t *c)
{
  .......
#if (NGX_THREADS)
 
  if (clcf->aio == NGX_HTTP_AIO_THREADS) {
    c->file.thread_task = c->thread_task;
    //这里注册的函数在下面语句中的ngx_thread_read函数中被调用
    c->file.thread_handler = ngx_http_cache_thread_handler;
    c->file.thread_ctx = r;
    //根据任务的属性，选择正确的线程池，并初始化task结构体中的各个成员    
    n = ngx_thread_read(&c->file, c->buf->pos, c->body_start, 0, r->pool);
 
    c->thread_task = c->file.thread_task;
    c->reading = (n == NGX_AGAIN);
 
    return n;
  }
#endif
 
  return ngx_read_file(&c->file, c->buf->pos, c->body_start, 0);
}
 
 
//task任务的处理函数
static ngx_int_t ngx_http_cache_thread_handler(ngx_thread_task_t *task, ngx_file_t *file)
{
  .......
  tp = clcf->thread_pool;
  .......
   
  task->event.data = r;
  //注册thread_event_handler函数，该函数在处理pool_done队列中event事件时被调用
  task->event.handler = ngx_http_cache_thread_event_handler;
 
  //将任务放到线程池的任务队列中
  if (ngx_thread_task_post(tp, task) != NGX_OK) {
    return NGX_ERROR;
  }
  ......
}
 
/*********************** nginx/src/core/ngx_thread_pool.c **********************/
//添加任务到队列中
ngx_int_t ngx_thread_task_post(ngx_thread_pool_t *tp, ngx_thread_task_t *task)
{
  //如果当前的任务正在处理就退出
  if (task->event.active) {
    ngx_log_error(NGX_LOG_ALERT, tp->log, 0,
           "task #%ui already active", task->id);
    return NGX_ERROR;
  }
 
  if (ngx_thread_mutex_lock(&tp->mtx, tp->log) != NGX_OK) {
    return NGX_ERROR;
  }
   
  //判断当前线程池等待的任务数量与最大队列长度的关系
  if (tp->waiting >= tp->max_queue) {
    (void) ngx_thread_mutex_unlock(&tp->mtx, tp->log);
 
    ngx_log_error(NGX_LOG_ERR, tp->log, 0,
           "thread pool \"%V\" queue overflow: %i tasks waiting",
           &tp->name, tp->waiting);
    return NGX_ERROR;
  }
  //激活任务
  task->event.active = 1;
 
  task->id = ngx_thread_pool_task_id++;
  task->next = NULL;
   
  //通知阻塞的线程有新事件加入，可以解除阻塞
  if (ngx_thread_cond_signal(&tp->cond, tp->log) != NGX_OK) {
    (void) ngx_thread_mutex_unlock(&tp->mtx, tp->log);
    return NGX_ERROR;
  }
 
  *tp->queue.last = task;
  tp->queue.last = &task->next;
 
  tp->waiting++;
 
  (void) ngx_thread_mutex_unlock(&tp->mtx, tp->log);
 
  ngx_log_debug2(NGX_LOG_DEBUG_CORE, tp->log, 0,
          "task #%ui added to thread pool \"%V\"",
          task->id, &tp->name);
 
  return NGX_OK;
}