Curl錯誤：Couldn't connect to server

在Linux系統下，開了200個線程分別curl同一個網站，結果程序爆錯了，一堆。
出錯信息：Couldn't connect to server
打開curl選項調試：
curl_easy_setopt(m_pCurl, CURLOPT_VERBOSE, 1);
也定位不了錯誤，後來發現200個線程，每次都有264個任務可以正常處理，而且程序的線程池會自動調度，空閒線程處理新任務，所以纔會有264這個數字。

我訪問的網站是在Windows創建的一個網站後臺，經過詢問，得知Windows的web服務器使用的是apache。

此時錯誤問題可以初步診斷爲：apache的最大連接數導致的問題。

於是經過一番修改（修改方法還是國外的，google偉大）：
原文：
It seems that the httpd-mpm.conf file holds the answer. But I'm not sure what settings should be changed or even what module apache is running as.

httpd-mpm.conf：

# prefork MPM
# StartServers: number of server processes to start
# MinSpareServers: minimum number of server processes which are kept spare
# MaxSpareServers: maximum number of server processes which are kept spare
# MaxClients: maximum number of server processes allowed to start
# MaxRequestsPerChild: maximum number of requests a server process serves
<IfModule mpm_prefork_module>
    StartServers          5
    MinSpareServers       5
    MaxSpareServers      10
    MaxClients          150
    MaxRequestsPerChild   0
</IfModule>

# worker MPM
# StartServers: initial number of server processes to start
# MaxClients: maximum number of simultaneous client connections
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadsPerChild: constant number of worker threads in each server process
# MaxRequestsPerChild: maximum number of requests a server process serves
<IfModule mpm_worker_module>
    StartServers          2
    MaxClients          150
    MinSpareThreads      25
    MaxSpareThreads      75 
    ThreadsPerChild      25
    MaxRequestsPerChild   0
</IfModule>

# BeOS MPM
# StartThreads: how many threads do we initially spawn?
# MaxClients:   max number of threads we can have (1 thread == 1 client)
# MaxRequestsPerThread: maximum number of requests each thread will process
<IfModule mpm_beos_module>
    StartThreads            10
    MaxClients              50
    MaxRequestsPerThread 10000
</IfModule>

# NetWare MPM
# ThreadStackSize: Stack size allocated for each worker thread
# StartThreads: Number of worker threads launched at server startup
# MinSpareThreads: Minimum number of idle threads, to handle request spikes
# MaxSpareThreads: Maximum number of idle threads
# MaxThreads: Maximum number of worker threads alive at the same time
# MaxRequestsPerChild: Maximum  number of requests a thread serves. It is 
#                      recommended that the default value of 0 be set for this
#                      directive on NetWare.  This will allow the thread to 
#                      continue to service requests indefinitely.                          
<IfModule mpm_netware_module>
    ThreadStackSize      65536
    StartThreads           250
    MinSpareThreads         25
    MaxSpareThreads        250
    MaxThreads            1000
    MaxRequestsPerChild      0
    MaxMemFree             100
</IfModule>

# OS/2 MPM
# StartServers: Number of server processes to maintain
# MinSpareThreads: Minimum number of idle threads per process, 
#                  to handle request spikes
# MaxSpareThreads: Maximum number of idle threads per process
# MaxRequestsPerChild: Maximum number of connections per server process
<IfModule mpm_mpmt_os2_module>
    StartServers           2
    MinSpareThreads        5
    MaxSpareThreads       10
    MaxRequestsPerChild    0
</IfModule>

# WinNT MPM
# ThreadsPerChild: constant number of worker threads in the server process
# MaxRequestsPerChild: maximum  number of requests a server process serves
<IfModule mpm_winnt_module>
    ThreadsPerChild      450
    MaxRequestsPerChild    0
</IfModule>

Answers：
The solution is to uncomment the MPM config include in httpd.conf

在httpd.conf文件中，打開該行註釋，否則修改無效：
# Server-pool management (MPM specific)
Include conf/extra/httpd-mpm.conf 

apache有2種模式：prefork和worker
通過執行：httpd.exe -l，結果裏面沒有prefork.c文件，說明本機的apache使用的是worker模式，於是就修改：

<IfModule mpm_worker_module>
    StartServers          2
    MaxClients          150 #最大連接數
    MinSpareThreads      25
    MaxSpareThreads      75 
    ThreadsPerChild      25 #每個子進程的服務線程數目
    MaxRequestsPerChild   0 #單個子進程在其生命週期內處理的總請求數限制，當某個子進程處理過的總請求數到達這個限制後這個進程就會被回收，如果設爲0，那麼這個進程永遠不會過期
</IfModule>

修改MaxClients值，重啓apache服務，問題解決！