Linux:Apache Access Log中的OPTIONS *的含义

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在Apache的Access Log中会看到很多如下的访问日志: - - [05/May/2011:10:54:07 +0800] "OPTIONS * HTTP/1.0" 200 - - - [05/May/2011:10:54:08 +0800] "OPTIONS * HTTP/1.0" 200 - - - [05/May/2011:10:54:09 +0800] "OPTIONS * HTTP/1.0" 200 - - - [05/May/2011:10:54:10 +0800] "OPTIONS * HTTP/1.0" 200 - 


Apache的文档中, 有如下的说明:

When the Apache HTTP Server manages its child processes, it needs a way to wake up processes that are listening for new connections. To do this, it sends a simple HTTP request back to itself. This request will appear in the access_log file with the remote address set to the loop-back interface (typically or ::1 if IPv6 is configured). If you log the User-Agent string (as in the combined log format), you will see the server signature followed by “(internal dummy connection)” on non-SSL servers. During certain periods you may see up to one such request for each httpd child process.

可是,为什么要唤醒呢? 唤醒是为了做什么呢?

Linux:Apache Access Log中的OPTIONS *的含义

Linux:Apache Access Log中的OPTIONS *的含义

在Apache Prefork模式下, 启动的时候,Apache就会fork出一些worker进程, 来准备接受请求, 这些worker进程,在完成准备工作以后, 就会进入block模式的监听沉睡中, 等待请求到来而被唤醒。

另外一方面, 在Prefork模式下, 当请求很多, 目前的worker进程数不够处理的时候, 就会额外再fork一些worker进程出来, 以满足当前的请求。

而在这些请求高峰过后, 如果额外fork出来的进程数大于了MaxSpareServers, Apache就会告诉这些worker进程退出, 那么问题就来了。

这些进程都在沉睡中啊, 怎么告诉他们, 并且让他们自我退出呢?

Apache会首先发送一个退出状态字(GRACEFUL_CHAR !)给这些Work进程:

static apr_status_t pod_signal_internal(ap_pod_t *pod)
    apr_status_t rv;
    char char_of_death = '!';
    apr_size_t one = 1;
    rv = apr_file_write(pod->pod_out, &char_of_death, &one);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_WARNING, rv, ap_server_conf,
                     "write pipe_of_death");
    return rv;

但此时, Worker进程不会去读这些状态字, 因为他们还在沉睡。

这个时候Apache就会发送一个OPTIONS请求给自己, 唤醒这些沉睡的进程:

static apr_status_t dummy_connection(ap_pod_t *pod)
    /* Create the request string. We include a User-Agent so that
     * adminstrators can track down the cause of the odd-looking
     * requests in their logs.
    srequest = apr_pstrcat(p, "OPTIONS * HTTP/1.0rnUser-Agent: ",
                           " (internal dummy connection)rnrn", NULL);

这些进程在处理完当前请求以后(OPTIONS请求), 就会发现, oh, 主进程让我退出。

static void child_main(int child_num_arg)
    while (!die_now && !shutdown_pending) {
        //1. listen
        //2. accept
        //3. process request
        /* Check the pod and the generation number after processing a
         * connection so that we'll go away if a graceful restart occurred
         * while we were processing the connection or we are the lucky
         * idle server process that gets to die.
        if (ap_mpm_pod_check(pod) == APR_SUCCESS) { /* selected as idle? */
            die_now = 1;

于是, 它就做完清理工作, 然后自我消亡了~~~


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