Libevent Source Code Analysis-----More Evbuffer operation functions

Reprint Please specify Source: http://blog.csdn.net/luotuo44/article/details/39325447

Lock Operation:

In the previous blog post you can see that many functions need to lock the evbuffer before operation. Unlike Event_base, if the evbuffer supports locks, the function evbuffer_enable_locking is called explicitly.

[CPP]  View Plain copy//buffer.c file    int//parameter can be a lock variable or null   evbuffer_enable_locking (struct  evbuffer *buf, void *lock)    {   #ifdef  _event_disable_thread_ support       return -1;   #else         if  (buf->lock)            return -1;           if  (!lock)  {            //self-assigning lock variables            evthread_alloc_lock ( lock, evthread_locktype_recursive);           if  (! Lock)                return -1;            buf->lock = lock;             //the Evbuffer has a lock, it needs to release the lock memory             buf->own_lock = 1;       } else {            buf->lock = lock;//lock        with parameters      buf->own_lock = 0;//himself did not own the lock. No need to release lock memory        }          return 0;    #endif   }  

As you can see, the second argument can be null. A lock is requested inside the function. Obviously if you want Evbuffer to be able to use a lock, you have to call Evthread_use_windows_threads () or evthread_use_pthreads () at the beginning, and you can refer to a blog post.

Because the user controls this Evbuffer, Libevent provides a lock and unlock interface for the user to use.[CPP]  View Plain copy//buffer.c file    void   evbuffer_lock (struct evbuffer *buf)     {       evbuffer_lock (buf);  }      void    Evbuffer_unlock (struct evbuffer *buf)    {       evbuffer _unlock (BUF);  }     //evbuffer-internal.h file    #define  evbuffer_ LOCK (buffer)                         \       do {                                  \            evlock_lock ((buffer)->lock, 0);               \