请问close-on-exec的实际意义

barbas

man fcntl

F_GETFD
              Read  the close-on-exec flag.  If the FD_CLOEXEC bit is 0, the file will remain open across exec, otherwise it
              will be closed.

       F_SETFD
              Set the close-on-exec flag to the value specified by the FD_CLOEXEC bit of arg.

这个，有什么实际的用途吗？因为我实在搞不清楚什么情况下需要设置这个位~~
求赐教

MMMIX

原帖由 barbas 于 2007-6-15 19:07 发表
man fcntl

F_GETFD
              Read  the close-on-exec flag.  If the FD_CLOEXEC bit is 0, the file will remain open across exec, otherwise it
              will be closed.

       F_SETFD
...

可以参考下这个：

The close-on-exec flag for a file descriptor tells whether the file descriptor should remain open across exec-calls. So when the Tcl interpreter has heaps of files open and the close-on-exec flag is not set, the exec'ed command will inherit all these file descriptors. If the close-on-exec flag is set on some file descriptors, those will be closed on exec, so that the subprocess cannot read/write the open descriptors and cannot keep the file open even if the Tcl interpreter terminates.

This would cause trouble if the file was to be deleted (which physically takes place when the file is no longer open) or - even worse - if the file is a pipe. In this case the other process dealing with the pipe will believe that there is still a reader/writer and won't detect EOF or "no reader present", hence keep waiting.

原文地址
http://athena.wolf.eu.org/~wolf/dupa/wiki.tcl.tk/6030

barbas

就是说平时还是不要多事去设F_SETFD啦？
那具体什么时候用啊？给个例子么~~
我看某些日志模块，打开日志文件后会setfd一把，也没想明白有什么必要……

MMMIX

原帖由 barbas 于 2007-6-15 19:45 发表
就是说平时还是不要多事去设F_SETFD啦？
那具体什么时候用啊？给个例子么~~
我看某些日志模块，打开日志文件后会setfd一把，也没想明白有什么必要……

老实说，我还真没有想到在什么地方非得用 close-on-exec 不可。不过在许多时候用这个很方便罢了，例如说不想让通过 exec 执行的程序继承 pipe 或者临时文件啥的。

barbas

嗯，受教，多谢~~

barbas

我知道会关闭，我只是很奇怪什么时候需要它关闭而已~~