From 0c8b6d85801c40cbe2a84d6edfe723f96595bc11 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Fri, 24 Apr 2020 01:46:52 +0200
Subject: [PATCH] bpo-38061: subprocess uses closefrom() on FreeBSD

Optimize the subprocess module on FreeBSD using closefrom().
A single close(fd) syscall is cheap, but when sysconf(_SC_OPEN_MAX)
is high, the loop calling close(fd) on each file descriptor can take
several milliseconds.

The workaround on FreeBSD to improve performance was to load and
mount the fdescfs kernel module, but this is not enabled by default.

Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans
(kevans) and Kubilay Kocak (koobs):
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
---
 Doc/whatsnew/3.9.rst                                  |  4 ++++
 .../Library/2020-04-24-01-55-00.bpo-38061.XmULB3.rst  | 11 +++++++++++
 Modules/_posixsubprocess.c                            |  8 +++++++-
 3 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-04-24-01-55-00.bpo-38061.XmULB3.rst

diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst
index ee851706055a30..325121df139816 100644
--- a/Doc/whatsnew/3.9.rst
+++ b/Doc/whatsnew/3.9.rst
@@ -471,6 +471,10 @@ Optimizations
   until the main thread handles signals.
   (Contributed by Victor Stinner in :issue:`40010`.)
 
+* Optimize the :mod:`subprocess` module on FreeBSD using ``closefrom()``.
+  (Contributed by Ed Maste, Conrad Meyer, Kyle Evans, Kubilay Kocak and Victor
+  Stinner in :issue:`38061`.)
+
 
 Build and C API Changes
 =======================
diff --git a/Misc/NEWS.d/next/Library/2020-04-24-01-55-00.bpo-38061.XmULB3.rst b/Misc/NEWS.d/next/Library/2020-04-24-01-55-00.bpo-38061.XmULB3.rst
new file mode 100644
index 00000000000000..603d80b88b074f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-04-24-01-55-00.bpo-38061.XmULB3.rst
@@ -0,0 +1,11 @@
+Optimize the :mod:`subprocess` module on FreeBSD using ``closefrom()``.
+A single ``close(fd)`` syscall is cheap, but when ``sysconf(_SC_OPEN_MAX)`` is
+high, the loop calling ``close(fd)`` on each file descriptor can take several
+milliseconds.
+
+The workaround on FreeBSD to improve performance was to load and mount the
+fdescfs kernel module, but this is not enabled by default.
+
+Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans (kevans) and
+Kubilay Kocak (koobs):
+https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index 7d5a7fe17c075e..60dd78d92a4f52 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -264,9 +264,15 @@ _close_fds_by_brute_force(long start_fd, PyObject *py_fds_to_keep)
         start_fd = keep_fd + 1;
     }
     if (start_fd <= end_fd) {
+#if defined(__FreeBSD__)
+        /* Any errors encountered while closing file descriptors are ignored */
+        closefrom(start_fd);
+#else
         for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
-            close(fd_num);
+            /* Ignore errors */
+            (void)close(fd_num);
         }
+#endif
     }
 }