bpo-41586: Add pipesize parameter to subprocess & F_GETPIPE_SZ and F_SETPIPE_SZ to fcntl. (GH-21921)
* 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.
diff --git a/Doc/library/fcntl.rst b/Doc/library/fcntl.rst
index 07a15d2..9d80211 100644
--- a/Doc/library/fcntl.rst
+++ b/Doc/library/fcntl.rst
@@ -39,6 +39,11 @@
On Linux(>=3.15), the fcntl module exposes the ``F_OFD_GETLK``, ``F_OFD_SETLK``
and ``F_OFD_SETLKW`` constants, which working with open file description locks.
+.. versionchanged:: 3.10
+ On Linux >= 2.6.11, the fcntl module exposes the ``F_GETPIPE_SZ`` and
+ ``F_SETPIPE_SZ`` constants, which allow to check and modify a pipe's size
+ respectively.
+
The module defines the following functions:
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index e37cc98..7993b10 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -341,7 +341,7 @@
startupinfo=None, creationflags=0, restore_signals=True, \
start_new_session=False, pass_fds=(), \*, group=None, \
extra_groups=None, user=None, umask=-1, \
- encoding=None, errors=None, text=None)
+ encoding=None, errors=None, text=None, pipesize=-1)
Execute a child program in a new process. On POSIX, the class uses
:meth:`os.execvp`-like behavior to execute the child program. On Windows,
@@ -625,6 +625,14 @@
* :data:`CREATE_DEFAULT_ERROR_MODE`
* :data:`CREATE_BREAKAWAY_FROM_JOB`
+ *pipesize* can be used to change the size of the pipe when
+ :data:`PIPE` is used for *stdin*, *stdout* or *stderr*. The size of the pipe
+ is only changed on platforms that support this (only Linux at this time of
+ writing). Other platforms will ignore this parameter.
+
+ .. versionadded:: 3.10
+ The ``pipesize`` parameter was added.
+
Popen objects are supported as context managers via the :keyword:`with` statement:
on exit, standard file descriptors are closed, and the process is waited for.
::
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 86fdf27..6a6c2fc 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -62,6 +62,11 @@
import grp
except ImportError:
grp = None
+try:
+ import fcntl
+except ImportError:
+ fcntl = None
+
__all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
"getoutput", "check_output", "run", "CalledProcessError", "DEVNULL",
@@ -756,7 +761,7 @@ def __init__(self, args, bufsize=-1, executable=None,
startupinfo=None, creationflags=0,
restore_signals=True, start_new_session=False,
pass_fds=(), *, user=None, group=None, extra_groups=None,
- encoding=None, errors=None, text=None, umask=-1):
+ encoding=None, errors=None, text=None, umask=-1, pipesize=-1):
"""Create new Popen instance."""
_cleanup()
# Held while anything is calling waitpid before returncode has been
@@ -773,6 +778,11 @@ def __init__(self, args, bufsize=-1, executable=None,
if not isinstance(bufsize, int):
raise TypeError("bufsize must be an integer")
+ if pipesize is None:
+ pipesize = -1 # Restore default
+ if not isinstance(pipesize, int):
+ raise TypeError("pipesize must be an integer")
+
if _mswindows:
if preexec_fn is not None:
raise ValueError("preexec_fn is not supported on Windows "
@@ -797,6 +807,7 @@ def __init__(self, args, bufsize=-1, executable=None,
self.returncode = None
self.encoding = encoding
self.errors = errors
+ self.pipesize = pipesize
# Validate the combinations of text and universal_newlines
if (text is not None and universal_newlines is not None
@@ -1575,6 +1586,8 @@ def _get_handles(self, stdin, stdout, stderr):
pass
elif stdin == PIPE:
p2cread, p2cwrite = os.pipe()
+ if self.pipesize > 0 and hasattr(fcntl, "F_SETPIPE_SZ"):
+ fcntl.fcntl(p2cwrite, fcntl.F_SETPIPE_SZ, self.pipesize)
elif stdin == DEVNULL:
p2cread = self._get_devnull()
elif isinstance(stdin, int):
@@ -1587,6 +1600,8 @@ def _get_handles(self, stdin, stdout, stderr):
pass
elif stdout == PIPE:
c2pread, c2pwrite = os.pipe()
+ if self.pipesize > 0 and hasattr(fcntl, "F_SETPIPE_SZ"):
+ fcntl.fcntl(c2pwrite, fcntl.F_SETPIPE_SZ, self.pipesize)
elif stdout == DEVNULL:
c2pwrite = self._get_devnull()
elif isinstance(stdout, int):
@@ -1599,6 +1614,8 @@ def _get_handles(self, stdin, stdout, stderr):
pass
elif stderr == PIPE:
errread, errwrite = os.pipe()
+ if self.pipesize > 0 and hasattr(fcntl, "F_SETPIPE_SZ"):
+ fcntl.fcntl(errwrite, fcntl.F_SETPIPE_SZ, self.pipesize)
elif stderr == STDOUT:
if c2pwrite != -1:
errwrite = c2pwrite
diff --git a/Lib/test/test_fcntl.py b/Lib/test/test_fcntl.py
index 7e10920..8d6e9ff 100644
--- a/Lib/test/test_fcntl.py
+++ b/Lib/test/test_fcntl.py
@@ -190,6 +190,19 @@ def test_fcntl_f_getpath(self):
res = fcntl.fcntl(self.f.fileno(), fcntl.F_GETPATH, bytes(len(expected)))
self.assertEqual(expected, res)
+ @unittest.skipIf(not (hasattr(fcntl, "F_SETPIPE_SZ") and hasattr(fcntl, "F_GETPIPE_SZ")),
+ "F_SETPIPE_SZ and F_GETPIPE_SZ are not available on all unix platforms.")
+ def test_fcntl_f_pipesize(self):
+ test_pipe_r, test_pipe_w = os.pipe()
+ # Get the default pipesize with F_GETPIPE_SZ
+ pipesize_default = fcntl.fcntl(test_pipe_w, fcntl.F_GETPIPE_SZ)
+ # Multiply the default with 2 to get a new value.
+ fcntl.fcntl(test_pipe_w, fcntl.F_SETPIPE_SZ, pipesize_default * 2)
+ self.assertEqual(fcntl.fcntl(test_pipe_w, fcntl.F_GETPIPE_SZ), pipesize_default * 2)
+ os.close(test_pipe_r)
+ os.close(test_pipe_w)
+
+
def test_main():
run_unittest(TestFcntl)
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 434ba56..8b576c0 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -39,6 +39,11 @@
except ImportError:
grp = None
+try:
+ import fcntl
+except:
+ fcntl = None
+
if support.PGO:
raise unittest.SkipTest("test is not helpful for PGO")
@@ -661,6 +666,46 @@ def test_stdin_devnull(self):
p.wait()
self.assertEqual(p.stdin, None)
+ def test_pipesizes(self):
+ # stdin redirection
+ pipesize = 16 * 1024
+ p = subprocess.Popen([sys.executable, "-c",
+ 'import sys; sys.stdin.read(); sys.stdout.write("out"); sys.stderr.write("error!")'],
+ stdin=subprocess.PIPE,
+ stdout=subprocess.PIPE,
+ stderr=subprocess.PIPE,
+ pipesize=pipesize)
+ # We only assert pipe size has changed on platforms that support it.
+ if sys.platform != "win32" and hasattr(fcntl, "F_GETPIPE_SZ"):
+ for fifo in [p.stdin, p.stdout, p.stderr]:
+ self.assertEqual(fcntl.fcntl(fifo.fileno(), fcntl.F_GETPIPE_SZ), pipesize)
+ # Windows pipe size can be acquired with the GetNamedPipeInfoFunction
+ # https://docs.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-getnamedpipeinfo
+ # However, this function is not yet in _winapi.
+ p.stdin.write(b"pear")
+ p.stdin.close()
+ p.wait()
+
+ def test_pipesize_default(self):
+ p = subprocess.Popen([sys.executable, "-c",
+ 'import sys; sys.stdin.read(); sys.stdout.write("out");'
+ ' sys.stderr.write("error!")'],
+ stdin=subprocess.PIPE,
+ stdout=subprocess.PIPE,
+ stderr=subprocess.PIPE,
+ pipesize=-1)
+ # UNIX tests using fcntl
+ if sys.platform != "win32" and hasattr(fcntl, "F_GETPIPE_SZ"):
+ fp_r, fp_w = os.pipe()
+ default_pipesize = fcntl.fcntl(fp_w, fcntl.F_GETPIPE_SZ)
+ for fifo in [p.stdin, p.stdout, p.stderr]:
+ self.assertEqual(
+ fcntl.fcntl(fifo.fileno(), fcntl.F_GETPIPE_SZ), default_pipesize)
+ # On other platforms we cannot test the pipe size (yet). But above code
+ # using pipesize=-1 should not crash.
+ p.stdin.close()
+ p.wait()
+
def test_env(self):
newenv = os.environ.copy()
newenv["FRUIT"] = "orange"
@@ -3503,7 +3548,7 @@ def test_getoutput(self):
def test__all__(self):
"""Ensure that __all__ is populated properly."""
- intentionally_excluded = {"list2cmdline", "Handle", "pwd", "grp"}
+ intentionally_excluded = {"list2cmdline", "Handle", "pwd", "grp", "fcntl"}
exported = set(subprocess.__all__)
possible_exports = set()
import types
diff --git a/Misc/ACKS b/Misc/ACKS
index d81d0a2..687bcb2 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1818,6 +1818,7 @@
Michael Vogt
Radu Voicilas
Alex Volkov
+Ruben Vorderman
Guido Vranken
Martijn Vries
Sjoerd de Vries
diff --git a/Misc/NEWS.d/next/Library/2020-08-19-08-32-13.bpo-41586.IYjmjK.rst b/Misc/NEWS.d/next/Library/2020-08-19-08-32-13.bpo-41586.IYjmjK.rst
new file mode 100644
index 0000000..4046167
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-08-19-08-32-13.bpo-41586.IYjmjK.rst
@@ -0,0 +1,2 @@
+Add F_SETPIPE_SZ and F_GETPIPE_SZ to fcntl module. Allow setting pipesize on
+subprocess.Popen.
diff --git a/Modules/fcntlmodule.c b/Modules/fcntlmodule.c
index afd2810..cdf0f9b 100644
--- a/Modules/fcntlmodule.c
+++ b/Modules/fcntlmodule.c
@@ -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;