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bpo-41586: Add pipesize parameter to subprocess & F_GETPIPE_SZ and F_SETPIPE_SZ to fcntl. (GH-21921)

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* Add F_SETPIPE_SZ and F_GETPIPE_SZ to fcntl module
* Add pipesize parameter for subprocess.Popen class

This will allow the user to control the size of the pipes.
On linux the default is 64K. When a pipe is full it blocks for writing.
When a pipe is empty it blocks for reading. On processes that are
very fast this can lead to a lot of wasted CPU cycles. On a typical
Linux system the max pipe size is 1024K which is much better.
For high performance-oriented libraries such as xopen it is nice to
be able to set the pipe size.

The workaround without this feature is to use my_popen_process.stdout.fileno() in
conjuction with fcntl and 1031 (value of F_SETPIPE_SZ) to acquire this behavior.
This commit is contained in:
Ruben Vorderman 2020-10-20 01:30:02 +02:00 • committed by GitHub
parent bf838227c3
commit 23c0fb8edd
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8 changed files with 102 additions and 3 deletions
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Modules/fcntlmodule.c
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@ -565,6 +565,14 @@ all_ins(PyObject* m)
if (PyModule_AddIntMacro(m, F_SHLCK)) return -1;
#endif
/* Linux specifics */
#ifdef F_SETPIPE_SZ
if (PyModule_AddIntMacro(m, F_SETPIPE_SZ)) return -1;
#endif
#ifdef F_GETPIPE_SZ
if (PyModule_AddIntMacro(m, F_GETPIPE_SZ)) return -1;
#endif
/* OS X specifics */
#ifdef F_FULLFSYNC
if (PyModule_AddIntMacro(m, F_FULLFSYNC)) return -1;