读取描述符的非阻塞调用 [英] Non-blocking call for reading descriptor

问题描述

我有一个 fd 描述符，我可以通过调用 read(fd, buffer,...) 来读取它.现在，我想在实际拨打电话之前检查是否有任何要阅读的内容，因为电话正在阻塞.我该怎么做?

I have a fd descriptor, which I can use to read from by calling read(fd, buffer,...). Now, I want to check if there is anything to read before actually making the call, because the call is blocking. How do I do this?

推荐答案

int flags = fcntl(fd, F_GETFL, 0);
fcntl(fd, F_SETFL, flags | O_NONBLOCK);

上面的代码片段将为非阻塞访问配置这样的描述符.如果调用 read 时数据不可用，则系统调用将失败并返回 -1 并且 errno 设置为 EAGAIN.有关详细信息，请参阅 fnctl 手册页.

The code snippet above will configure such a descriptor for non-blocking access. If data is not available when you call read, then the system call will fail with a return value of -1 and errno is set to EAGAIN. See the fnctl man pages for more information.

或者，您可以使用带有可配置超时的 select 来检查和/或等待更多数据的指定时间间隔.这种方法可能正是您想要的，而且效率更高.

Alternatively, you can use select with a configurable timeout to check and/or wait a specified time interval for more data. This method is probably what you want and can be much more efficient.

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