bpo-41586: Add pipesize parameter to subprocess. Add F_GETPIPE_SZ and F_SETPIPE_SZ to fcntl.

Doc/library/fcntl.rst

@@ -39,6 +39,11 @@ descriptor.
  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:
 
 

Doc/library/subprocess.rst

@@ -341,7 +341,7 @@ functions.
  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 @@ functions.
  * :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.
  ::

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

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)
 

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

Misc/ACKS

@@ -1805,6 +1805,7 @@ Johannes Vogel
 Michael Vogt
 Radu Voicilas
 Alex Volkov
+Ruben Vorderman
 Guido Vranken
 Martijn Vries
 Sjoerd de Vries

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.

Modules/fcntlmodule.c

@@ -577,6 +577,14 @@ 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;