内核负责将进程转移到睡眠状态、等待套接字做好写入的准备、读取 TCP 状态代码，等等。

The kernel takes care of moving the process to sleeping state, waiting for the socket to be ready for writing, reading the TCP status code, and so on.

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要等待某个事件，则可以使用 semop() 函数，并将 sem_op 的值设置为 -1，这样就可以阻塞调用进程，直到它变为有信号状态为止。

To wait on an event, semop() function is used with sem_op value as -1 thus blocking the calling process until it is signaled.

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这一次的操作是同步进行的，并且服务器进程在客户端向其发出调用之前一直处于等待状态的。

This time the operation is synchronous, and the server process waits for the go ahead before the call returns to the client.

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