From 1e51d96c0f5226be1a5b06975890e572fb4feecd Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Tue, 18 Aug 2020 15:14:47 +0200
Subject: [PATCH 01/17] Add F_SETPIPE_SZ and F_GETPIPE_SZ to fcntl module

---
 Modules/fcntlmodule.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Modules/fcntlmodule.c b/Modules/fcntlmodule.c
index 39baea01ec84ea..50748c7c13f8e9 100644
--- a/Modules/fcntlmodule.c
+++ b/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;

From a218c3902f4f79036d2010e16db72b4608e3a356 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Tue, 18 Aug 2020 15:38:07 +0200
Subject: [PATCH 02/17] Add pipesize parameter for 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 current workaround is to use my_popen_process.stdout.fileno() in
conjuction with fcntl and 1031 (value of F_SETPIPE_SZ) to acquire this
behavior.
---
 Lib/subprocess.py | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 86fdf27f9b03bd..1e0b55d0471226 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -62,6 +62,13 @@
     import grp
 except ImportError:
     grp = None
+try:
+    import fcntl
+    from fcntl import F_SETPIPE_SZ
+except ImportError:
+    fcntl = None
+    F_SETPIPE_SZ = None
+
 
 __all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
            "getoutput", "check_output", "run", "CalledProcessError", "DEVNULL",
@@ -756,7 +763,7 @@ 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
@@ -770,9 +777,12 @@ def __init__(self, args, bufsize=-1, executable=None,
         self._communication_started = False
         if bufsize is None:
             bufsize = -1  # Restore default
+        if pipesize is None:
+            pipesize = -1  # Restore default
         if not isinstance(bufsize, int):
             raise TypeError("bufsize must be an integer")
-
+        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 fcntl and self.pipesize > 0:
+                    fcntl.fcntl(p2cwrite, 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 fcntl and self.pipesize > 0:
+                    fcntl.fcntl(c2pwrite, 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 fcntl and self.pipesize > 0:
+                    fcntl.fcntl(errwrite, F_SETPIPE_SZ, self.pipesize)
             elif stderr == STDOUT:
                 if c2pwrite != -1:
                     errwrite = c2pwrite

From 02b1d43762b65e0763c3b8cbde632848e60f26df Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Tue, 18 Aug 2020 16:03:29 +0200
Subject: [PATCH 03/17] Add test for F_SETPIPE_SZ and F_GETPIPE_SZ

---
 Lib/test/test_fcntl.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/Lib/test/test_fcntl.py b/Lib/test/test_fcntl.py
index 7e1092083269e4..ef223d869bf475 100644
--- a/Lib/test/test_fcntl.py
+++ b/Lib/test/test_fcntl.py
@@ -72,11 +72,14 @@ class TestFcntl(unittest.TestCase):
 
     def setUp(self):
         self.f = None
+        self.testpipe_path = "testpipe"
 
     def tearDown(self):
         if self.f and not self.f.closed:
             self.f.close()
         unlink(TESTFN)
+        if os.path.exists(self.testpipe_path):
+            unlink(self.testpipe_path)
 
     def test_fcntl_fileno(self):
         # the example from the library docs
@@ -190,6 +193,16 @@ def test_fcntl_f_getpath(self):
         res = fcntl.fcntl(self.f.fileno(), fcntl.F_GETPATH, bytes(len(expected)))
         self.assertEqual(expected, res)
 
+    @unittest.skipIf(sys.platform != 'linux', "F_SETPIPE_SZ and F_GETPIPE_SZ are only available on linux")
+    def test_fcntl_f_pipesize(self):
+        os.mkfifo(self.testpipe_path)
+        test_pipe_fd = os.open(self.testpipe_path, os.O_RDWR)
+        pipesize = 16 * 1024  # 64K is linux default.
+        self.assertNotEqual(fcntl.fcntl(test_pipe_fd, fcntl.F_GETPIPE_SZ), pipesize)
+        fcntl.fcntl(test_pipe_fd, fcntl.F_SETPIPE_SZ, pipesize)
+        self.assertEqual(fcntl.fcntl(test_pipe_fd, fcntl.F_GETPIPE_SZ), pipesize)
+
+
 def test_main():
     run_unittest(TestFcntl)
 

From af05503ef129f9ef0433ab793bb0f60e4c6b805c Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Tue, 18 Aug 2020 16:49:30 +0200
Subject: [PATCH 04/17] Ensure cross-platform compatibility for pipesize in
 subprocess.Popen

---
 Lib/subprocess.py | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 1e0b55d0471226..0e0c3057868372 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -64,10 +64,8 @@
     grp = None
 try:
     import fcntl
-    from fcntl import F_SETPIPE_SZ
 except ImportError:
     fcntl = None
-    F_SETPIPE_SZ = None
 
 
 __all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
@@ -1258,11 +1256,11 @@ def _get_handles(self, stdin, stdout, stderr):
             if stdin is None:
                 p2cread = _winapi.GetStdHandle(_winapi.STD_INPUT_HANDLE)
                 if p2cread is None:
-                    p2cread, _ = _winapi.CreatePipe(None, 0)
+                    p2cread, _ = _winapi.CreatePipe(None, self.pipesize)
                     p2cread = Handle(p2cread)
                     _winapi.CloseHandle(_)
             elif stdin == PIPE:
-                p2cread, p2cwrite = _winapi.CreatePipe(None, 0)
+                p2cread, p2cwrite = _winapi.CreatePipe(None, self.pipesize)
                 p2cread, p2cwrite = Handle(p2cread), Handle(p2cwrite)
             elif stdin == DEVNULL:
                 p2cread = msvcrt.get_osfhandle(self._get_devnull())
@@ -1276,11 +1274,11 @@ def _get_handles(self, stdin, stdout, stderr):
             if stdout is None:
                 c2pwrite = _winapi.GetStdHandle(_winapi.STD_OUTPUT_HANDLE)
                 if c2pwrite is None:
-                    _, c2pwrite = _winapi.CreatePipe(None, 0)
+                    _, c2pwrite = _winapi.CreatePipe(None, self.pipesize)
                     c2pwrite = Handle(c2pwrite)
                     _winapi.CloseHandle(_)
             elif stdout == PIPE:
-                c2pread, c2pwrite = _winapi.CreatePipe(None, 0)
+                c2pread, c2pwrite = _winapi.CreatePipe(None, self.pipesize)
                 c2pread, c2pwrite = Handle(c2pread), Handle(c2pwrite)
             elif stdout == DEVNULL:
                 c2pwrite = msvcrt.get_osfhandle(self._get_devnull())
@@ -1294,11 +1292,11 @@ def _get_handles(self, stdin, stdout, stderr):
             if stderr is None:
                 errwrite = _winapi.GetStdHandle(_winapi.STD_ERROR_HANDLE)
                 if errwrite is None:
-                    _, errwrite = _winapi.CreatePipe(None, 0)
+                    _, errwrite = _winapi.CreatePipe(None, self.pipesize)
                     errwrite = Handle(errwrite)
                     _winapi.CloseHandle(_)
             elif stderr == PIPE:
-                errread, errwrite = _winapi.CreatePipe(None, 0)
+                errread, errwrite = _winapi.CreatePipe(None, self.pipesize)
                 errread, errwrite = Handle(errread), Handle(errwrite)
             elif stderr == STDOUT:
                 errwrite = c2pwrite
@@ -1586,8 +1584,8 @@ def _get_handles(self, stdin, stdout, stderr):
                 pass
             elif stdin == PIPE:
                 p2cread, p2cwrite = os.pipe()
-                if fcntl and self.pipesize > 0:
-                    fcntl.fcntl(p2cwrite, F_SETPIPE_SZ, self.pipesize)
+                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):
@@ -1600,8 +1598,8 @@ def _get_handles(self, stdin, stdout, stderr):
                 pass
             elif stdout == PIPE:
                 c2pread, c2pwrite = os.pipe()
-                if fcntl and self.pipesize > 0:
-                    fcntl.fcntl(c2pwrite, F_SETPIPE_SZ, self.pipesize)
+                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):
@@ -1614,8 +1612,8 @@ def _get_handles(self, stdin, stdout, stderr):
                 pass
             elif stderr == PIPE:
                 errread, errwrite = os.pipe()
-                if fcntl and self.pipesize > 0:
-                    fcntl.fcntl(errwrite, F_SETPIPE_SZ, self.pipesize)
+                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

From 493d6c3b9a417609b3e8765bcbd0bbbc29e88248 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Tue, 18 Aug 2020 16:49:55 +0200
Subject: [PATCH 05/17] Add linux test for pipesize in subprocess

---
 Lib/test/test_subprocess.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 434ba567db0a56..e560e662688819 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -10,6 +10,7 @@
 import io
 import itertools
 import os
+import fcntl
 import errno
 import tempfile
 import time
@@ -661,6 +662,22 @@ def test_stdin_devnull(self):
         p.wait()
         self.assertEqual(p.stdin, None)
 
+    @unittest.skipIf(sys.platform != "linux", "Pipe size can only be set on linux.")
+    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)
+        for fifo in [p.stdin, p.stdout, p.stderr]:
+            self.assertEqual(fcntl.fcntl(fifo.fileno(), fcntl.F_GETPIPE_SZ), pipesize)
+        p.stdin.write(b"pear")
+        p.stdin.close()
+        p.wait()
+
     def test_env(self):
         newenv = os.environ.copy()
         newenv["FRUIT"] = "orange"

From aad24c600c884a12325b383681ad6c149d60edda Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Wed, 19 Aug 2020 08:25:13 +0200
Subject: [PATCH 06/17] Enable subprocess pipesize test for all platforms

Windows does support changing pipesize, but currently _winapi does not support measuring it. Hence the pipesize cannot be tested on this platform (yet).
---
 Lib/test/test_subprocess.py | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index e560e662688819..1bcf0a6abeadda 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -10,7 +10,6 @@
 import io
 import itertools
 import os
-import fcntl
 import errno
 import tempfile
 import time
@@ -40,6 +39,11 @@
 except ImportError:
     grp = None
 
+try:
+    import fcntl
+except:
+    fcntl = None
+
 if support.PGO:
     raise unittest.SkipTest("test is not helpful for PGO")
 
@@ -662,7 +666,6 @@ def test_stdin_devnull(self):
         p.wait()
         self.assertEqual(p.stdin, None)
 
-    @unittest.skipIf(sys.platform != "linux", "Pipe size can only be set on linux.")
     def test_pipesizes(self):
         # stdin redirection
         pipesize = 16 * 1024
@@ -672,8 +675,13 @@ def test_pipesizes(self):
                              stdout=subprocess.PIPE,
                              stderr=subprocess.PIPE,
                          pipesize=pipesize)
-        for fifo in [p.stdin, p.stdout, p.stderr]:
-            self.assertEqual(fcntl.fcntl(fifo.fileno(), fcntl.F_GETPIPE_SZ), 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()

From acf9ae4f53ae84ae3c1a410778c7d144a8716c34 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Wed, 19 Aug 2020 08:28:01 +0200
Subject: [PATCH 07/17] Do not set pipesizes for Popen on Windows, as this can
 not be tested as of yet

---
 Lib/subprocess.py | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 0e0c3057868372..6a6c2fc98e83f3 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -775,12 +775,14 @@ def __init__(self, args, bufsize=-1, executable=None,
         self._communication_started = False
         if bufsize is None:
             bufsize = -1  # Restore default
-        if pipesize is None:
-            pipesize = -1  # Restore default
         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 "
@@ -1256,11 +1258,11 @@ def _get_handles(self, stdin, stdout, stderr):
             if stdin is None:
                 p2cread = _winapi.GetStdHandle(_winapi.STD_INPUT_HANDLE)
                 if p2cread is None:
-                    p2cread, _ = _winapi.CreatePipe(None, self.pipesize)
+                    p2cread, _ = _winapi.CreatePipe(None, 0)
                     p2cread = Handle(p2cread)
                     _winapi.CloseHandle(_)
             elif stdin == PIPE:
-                p2cread, p2cwrite = _winapi.CreatePipe(None, self.pipesize)
+                p2cread, p2cwrite = _winapi.CreatePipe(None, 0)
                 p2cread, p2cwrite = Handle(p2cread), Handle(p2cwrite)
             elif stdin == DEVNULL:
                 p2cread = msvcrt.get_osfhandle(self._get_devnull())
@@ -1274,11 +1276,11 @@ def _get_handles(self, stdin, stdout, stderr):
             if stdout is None:
                 c2pwrite = _winapi.GetStdHandle(_winapi.STD_OUTPUT_HANDLE)
                 if c2pwrite is None:
-                    _, c2pwrite = _winapi.CreatePipe(None, self.pipesize)
+                    _, c2pwrite = _winapi.CreatePipe(None, 0)
                     c2pwrite = Handle(c2pwrite)
                     _winapi.CloseHandle(_)
             elif stdout == PIPE:
-                c2pread, c2pwrite = _winapi.CreatePipe(None, self.pipesize)
+                c2pread, c2pwrite = _winapi.CreatePipe(None, 0)
                 c2pread, c2pwrite = Handle(c2pread), Handle(c2pwrite)
             elif stdout == DEVNULL:
                 c2pwrite = msvcrt.get_osfhandle(self._get_devnull())
@@ -1292,11 +1294,11 @@ def _get_handles(self, stdin, stdout, stderr):
             if stderr is None:
                 errwrite = _winapi.GetStdHandle(_winapi.STD_ERROR_HANDLE)
                 if errwrite is None:
-                    _, errwrite = _winapi.CreatePipe(None, self.pipesize)
+                    _, errwrite = _winapi.CreatePipe(None, 0)
                     errwrite = Handle(errwrite)
                     _winapi.CloseHandle(_)
             elif stderr == PIPE:
-                errread, errwrite = _winapi.CreatePipe(None, self.pipesize)
+                errread, errwrite = _winapi.CreatePipe(None, 0)
                 errread, errwrite = Handle(errread), Handle(errwrite)
             elif stderr == STDOUT:
                 errwrite = c2pwrite

From 6815aaa293ef6bac30e80d7f57f192af5fa24a64 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Wed, 19 Aug 2020 08:29:04 +0200
Subject: [PATCH 08/17] Add F_GETPIPE_SZ, F_SETPIPE_SZ and subprocess.Popen
 pipesize argument to the docs

---
 Doc/library/fcntl.rst      | 5 +++++
 Doc/library/subprocess.rst | 8 +++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/Doc/library/fcntl.rst b/Doc/library/fcntl.rst
index 07a15d27216e92..9d8021150c42f5 100644
--- a/Doc/library/fcntl.rst
+++ b/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:
 
 
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index e37cc980e97575..a7f20881b45618 100644
--- a/Doc/library/subprocess.rst
+++ b/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 +625,12 @@ functions.
       * :data:`CREATE_DEFAULT_ERROR_MODE`
       * :data:`CREATE_BREAKAWAY_FROM_JOB`
 
+   ``pipesize`` can be used to change the size of the pipe when
+   ``subprocess.PIPE`` is used for ``stdin``,``stdout`` or ``stderr`` on Linux.
+
+   .. 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.
    ::

From 6bfd6a5b1958847addae142e229d63c2a81898f8 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Wed, 19 Aug 2020 08:30:11 +0200
Subject: [PATCH 09/17] Add Ruben Vorderman to ACKS for work on the pipesize
 parameter in subprocess.Popen

---
 Misc/ACKS | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Misc/ACKS b/Misc/ACKS
index 1599b09c692b75..f018aa436e7ccf 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1805,6 +1805,7 @@ Johannes Vogel
 Michael Vogt
 Radu Voicilas
 Alex Volkov
+Ruben Vorderman
 Guido Vranken
 Martijn Vries
 Sjoerd de Vries

From cf97235ec1fe6c1d41fb51865827ff83caa82b84 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Wed, 19 Aug 2020 08:33:02 +0200
Subject: [PATCH 10/17] Add blurb for bpo 41586

---
 .../next/Library/2020-08-19-08-32-13.bpo-41586.IYjmjK.rst       | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2020-08-19-08-32-13.bpo-41586.IYjmjK.rst

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 00000000000000..40461679ebdfeb
--- /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.

From 389e4e9643f4974df246a7aaf71371b7e9b6e2a2 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Wed, 19 Aug 2020 09:11:42 +0200
Subject: [PATCH 11/17] Simplify test fore F_GETPIPE_SZ and F_SETPIPE_SZ so no
 file cleanup is needed.

---
 Lib/test/test_fcntl.py | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/Lib/test/test_fcntl.py b/Lib/test/test_fcntl.py
index ef223d869bf475..5965ece4691bbd 100644
--- a/Lib/test/test_fcntl.py
+++ b/Lib/test/test_fcntl.py
@@ -72,14 +72,11 @@ class TestFcntl(unittest.TestCase):
 
     def setUp(self):
         self.f = None
-        self.testpipe_path = "testpipe"
 
     def tearDown(self):
         if self.f and not self.f.closed:
             self.f.close()
         unlink(TESTFN)
-        if os.path.exists(self.testpipe_path):
-            unlink(self.testpipe_path)
 
     def test_fcntl_fileno(self):
         # the example from the library docs
@@ -195,12 +192,13 @@ def test_fcntl_f_getpath(self):
 
     @unittest.skipIf(sys.platform != 'linux', "F_SETPIPE_SZ and F_GETPIPE_SZ are only available on linux")
     def test_fcntl_f_pipesize(self):
-        os.mkfifo(self.testpipe_path)
-        test_pipe_fd = os.open(self.testpipe_path, os.O_RDWR)
+        test_pipe_r, test_pipe_w = os.pipe()
         pipesize = 16 * 1024  # 64K is linux default.
-        self.assertNotEqual(fcntl.fcntl(test_pipe_fd, fcntl.F_GETPIPE_SZ), pipesize)
-        fcntl.fcntl(test_pipe_fd, fcntl.F_SETPIPE_SZ, pipesize)
-        self.assertEqual(fcntl.fcntl(test_pipe_fd, fcntl.F_GETPIPE_SZ), pipesize)
+        self.assertNotEqual(fcntl.fcntl(test_pipe_w, fcntl.F_GETPIPE_SZ), pipesize)
+        fcntl.fcntl(test_pipe_w, fcntl.F_SETPIPE_SZ, pipesize)
+        self.assertEqual(fcntl.fcntl(test_pipe_w, fcntl.F_GETPIPE_SZ), pipesize)
+        os.close(test_pipe_r)
+        os.close(test_pipe_w)
 
 
 def test_main():

From e601174250c83a76e60550d45b93e1720796bd88 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Wed, 19 Aug 2020 09:28:11 +0200
Subject: [PATCH 12/17] Test F_SETPIPE_SZ and F_GETPIPE_SZ on all supported
 platforms

---
 Lib/test/test_fcntl.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_fcntl.py b/Lib/test/test_fcntl.py
index 5965ece4691bbd..b3c0b067efa3be 100644
--- a/Lib/test/test_fcntl.py
+++ b/Lib/test/test_fcntl.py
@@ -190,7 +190,8 @@ def test_fcntl_f_getpath(self):
         res = fcntl.fcntl(self.f.fileno(), fcntl.F_GETPATH, bytes(len(expected)))
         self.assertEqual(expected, res)
 
-    @unittest.skipIf(sys.platform != 'linux', "F_SETPIPE_SZ and F_GETPIPE_SZ are only available on linux")
+    @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()
         pipesize = 16 * 1024  # 64K is linux default.

From 24f061b4e4bdede02c9a3eacb854b46a13f6b094 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Wed, 19 Aug 2020 10:48:53 +0200
Subject: [PATCH 13/17] Intentionally exclude fcntl from subprocess.__all__
 test.

fcntl is not available on Windows.
---
 Lib/test/test_subprocess.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 1bcf0a6abeadda..1df6e727f99f99 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -3528,7 +3528,7 @@ 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

From 58925f3bdeaa904b64e8e5257c594c1268c9de47 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Wed, 19 Aug 2020 11:06:32 +0200
Subject: [PATCH 14/17] Properly format the pipesize argument in the subprocess
 docs.

---
 Doc/library/subprocess.rst | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index a7f20881b45618..17a956f466b434 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -625,8 +625,9 @@ functions.
       * :data:`CREATE_DEFAULT_ERROR_MODE`
       * :data:`CREATE_BREAKAWAY_FROM_JOB`
 
-   ``pipesize`` can be used to change the size of the pipe when
-   ``subprocess.PIPE`` is used for ``stdin``,``stdout`` or ``stderr`` on Linux.
+   *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.
 
    .. versionadded:: 3.10
       The ``pipesize`` parameter was added.

From 15b759e928e4322c8aab5ebcb46dd3a9116d8f88 Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Mon, 24 Aug 2020 09:42:29 +0200
Subject: [PATCH 15/17] Determine default dynamically

---
 Lib/test/test_fcntl.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/Lib/test/test_fcntl.py b/Lib/test/test_fcntl.py
index b3c0b067efa3be..8d6e9ff788454f 100644
--- a/Lib/test/test_fcntl.py
+++ b/Lib/test/test_fcntl.py
@@ -194,10 +194,11 @@ def test_fcntl_f_getpath(self):
                      "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()
-        pipesize = 16 * 1024  # 64K is linux default.
-        self.assertNotEqual(fcntl.fcntl(test_pipe_w, fcntl.F_GETPIPE_SZ), pipesize)
-        fcntl.fcntl(test_pipe_w, fcntl.F_SETPIPE_SZ, pipesize)
-        self.assertEqual(fcntl.fcntl(test_pipe_w, fcntl.F_GETPIPE_SZ), pipesize)
+        # 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)
 

From d4d08869f71441010dfbf8d9b7d6660249ec4bdf Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Mon, 24 Aug 2020 09:56:23 +0200
Subject: [PATCH 16/17] Add test for pipesize default

---
 Lib/test/test_subprocess.py | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 1df6e727f99f99..8b576c036ef0d2 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -686,6 +686,26 @@ def test_pipesizes(self):
         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"

From c129ca8225e81c349b8aa3c3e6bde383b1fcc94d Mon Sep 17 00:00:00 2001
From: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
Date: Mon, 24 Aug 2020 10:00:29 +0200
Subject: [PATCH 17/17] Add a note to the documentation about only Linux
 supporting the pipesize parameter

---
 Doc/library/subprocess.rst | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index 17a956f466b434..7993b103f473e2 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -627,7 +627,8 @@ functions.
 
    *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.
+   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.