在Apache的Access Log中会看到很多如下的访问日志：
127.0.0.1 - - [05/May/2011:10:54:07 +0800] "OPTIONS * HTTP/1.0" 200 -
127.0.0.1 - - [05/May/2011:10:54:08 +0800] "OPTIONS * HTTP/1.0" 200 -
127.0.0.1 - - [05/May/2011:10:54:09 +0800] "OPTIONS * HTTP/1.0" 200 -
127.0.0.1 - - [05/May/2011:10:54:10 +0800] "OPTIONS * HTTP/1.0" 200 -
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;
}
{
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)
{
//...有省略
/* 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/1.0\r\nUser-Agent: ",
ap_get_server_banner(),
" (internal dummy connection)\r\n\r\n", NULL);
//...有省略
}
{
//...有省略
/* 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/1.0\r\nUser-Agent: ",
ap_get_server_banner(),
" (internal dummy connection)\r\n\r\n", NULL);
//...有省略
}
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)
{
//...有省略
while (!die_now && !shutdown_pending) {
//...有省略
//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;
}
//...有省略
}
//...有省略
}
{
//...有省略
while (!die_now && !shutdown_pending) {
//...有省略
//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;
}
//...有省略
}
//...有省略
}
于是， 它就做完清理工作， 然后自我消亡了~~~
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