POLLHUP vs POLLNVAL vs EPOLLHUP

最新推荐文章于 2023-12-04 07:00:00 发布

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最新推荐文章于 2023-12-04 07:00:00 发布 · 1.2k 阅读

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POLLNVAL

POLLNVALis equivalent to EBADF: it means the file descriptor does not actually refer to any open file, i.e. it was closed or never open to begin with. This can never happen except as a result of a programming error or intentional attempt to query whether a file descriptor is invalid. External conditions, such as a peer closing its end of a network socket or pipe, can never close your file descriptor to your end of the socket or pipe. If it could, this would lead to massive vulnerabilities in basically any program using sockets/pipes/etc.
也就是说当文件描述符没有打开,或者实际上并未引用任何打开的文件,会有这个事件.
除非由于编程错误或故意尝试查询文件描述符是否无效，否则这种情况永远不会发生。

POLLHUP

相反,是说你这个fd是有效的, 但是处于这样一个状态:
A device has been disconnected, or a pipe or FIFO has been closed by the last process that had it open for writing. Once set, the hangup state of a FIFO shall persist until some process opens the FIFO for writing