subprocess, buffered files, pipes and broken pipe errors
Hi, => I propose to ignore BrokenPipeError on Popen.__exit__(), what do you think? A recent issue fixed subprocess.Popen.__exit__() to read the exit status of the child process, even if stdin.close() raised a BrokenPipeError: http://bugs.python.org/issue21619 When I saw the issue, I was surprised that Popen.__exit__() doesn't ignore BrokenPipeError. Popen.communicate() is designed to handle corner cases and it ignores BrokenPipeError. Popen.__exit__() only returns when the process exited. The method starts by closing all pipes. Usually the child process notices that stdin was closed and exit (programs used as "pipes" like grep, cat, wc, etc.). The problem is that Popen uses a buffered writer for Popen.stdin with a default buffer size of 8 KB. We may buffer some data and so stdin.close() will call stdin.write(). If the child process exited or closed stdin, the pipe is broken, and the write in the parent process (stdin.close() in Popen.__exit__) will raise BrokenPipeError. I propose to ignore BrokenPipeError in Popen.__exit__, as done in communicate(), for convinience: http://bugs.python.org/issue23570 Serhiy wants to keep BrokenPipeError, he wrote that file.close() should not ignore write errors (read the issue for details). I consider that BrokenPipeError on a pipe is different than a write error on a regular file. EPIPE and SIGPIPE are designed to notify that the pipe is closed and that it's now inefficient to continue to write into this pipe. Ignoring BrokenPipeError in Popen.__exit__() respects this constrain because the method closes stdin and only returns when the process exited. So the caller will not write anything into stdin anymore. What do you think? Victor
On 06.03.15 14:53, Victor Stinner wrote:
I rather said about file.__exit__.
And into the file like open('/dev/stdout', 'wb').
And the caller will not write anything into the file after calling file.__exit__. I don't see large difference between open('file', 'wb') and Popen('cat
file', stdin=PIPE), between sys.stdout with redirecting stdout and running external program with Pipe().
On 06.03.15 14:53, Victor Stinner wrote:
I rather said about file.__exit__.
And into the file like open('/dev/stdout', 'wb').
And the caller will not write anything into the file after calling file.__exit__. I don't see large difference between open('file', 'wb') and Popen('cat
file', stdin=PIPE), between sys.stdout with redirecting stdout and running external program with Pipe().
participants (2)
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Serhiy Storchaka -
Victor Stinner