lang/python{27,35,36,37,38}: Add closefrom(2) support

A single close(fd) syscall is cheap, but when MAXFDS (maximum file
descriptor number) is high, the loop calling close(fd) on each file
descriptor can take several milliseconds.

The default value of subprocess.Popen "close_fds" parameter changed to True
in Python 3. Compared to Python 2, close_fds=True can make Popen 10x
slower: see bpo-37790 [1]

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

This change adds minimum viable (and upstreamable) closefrom(2) syscall
support to Python's subprocess and posix modules, improving performance
significantly for loads that involve working with many processes, such as
diffoscope, ansible, and many others.

For additional optimizations, upstream recently (3.8) landed posix_spawn(2)
support [3] and has stated that they will adopt close_range(2) after Linux
merges it [4]. Linux/FreeBSD developers are already collaborating on
ensuring compatible implementations, with FreeBSD's implementation pending
in D21627. [5]

Thank you emaste, cem, kevans for providing analysis, input,
clarifications, comms/upstream support and patches.

[1] https://bugs.python.org/issue37790
[2] https://bugs.python.org/issue38061
[3] https://bugs.python.org/issue35537
[4] https://lwn.net/Articles/789023/
[5] https://reviews.freebsd.org/D21627

Additional References:

https://bugs.python.org/issue8052
https://bugs.python.org/issue11284
https://bugs.python.org/issue13788
https://bugs.python.org/issue1663329
https://www.python.org/dev/peps/pep-0446/

PR:		242274, 221700
Submitted by:	kevans (emaste, cem)
Approved by:	koobs (python (maintainer), santa)

14 files changed, 237 insertions, 2 deletions

diff --git a/lang/python27/Makefile b/lang/python27/Makefile
index 717f0296b46e..6ecb0882b96c 100644
--- a/lang/python27/Makefile
+++ b/lang/python27/Makefile
@@ -2,6 +2,7 @@
 
 PORTNAME=	python
 PORTVERSION=	${PYTHON_PORTVERSION}
+PORTREVISION=	1
 CATEGORIES=	lang python
 MASTER_SITES=	PYTHON/ftp/python/${PORTVERSION}
 PKGNAMESUFFIX=	27
diff --git a/lang/python27/files/patch-Modules_posixmodule.c b/lang/python27/files/patch-Modules_posixmodule.c
new file mode 100644
index 000000000000..acc841e5c199
--- /dev/null
+++ b/lang/python27/files/patch-Modules_posixmodule.c
@@ -0,0 +1,27 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/posixmodule.c.orig	2019-10-19 18:38:44 UTC
++++ Modules/posixmodule.c
+@@ -6676,9 +6676,16 @@ posix_closerange(PyObject *self, PyObject *args)
+     if (!PyArg_ParseTuple(args, "ii:closerange", &fd_from, &fd_to))
+         return NULL;
+     Py_BEGIN_ALLOW_THREADS
+-    for (i = fd_from; i < fd_to; i++)
+-        if (_PyVerify_fd(i))
+-            close(i);
++#ifdef __FreeBSD__
++    if (fd_to >= sysconf(_SC_OPEN_MAX)) {
++        closefrom(fd_from);
++    } else
++#endif
++    {
++        for (i = fd_from; i < fd_to; i++)
++            if (_PyVerify_fd(i))
++                close(i);
++    }
+     Py_END_ALLOW_THREADS
+     Py_RETURN_NONE;
+ }
diff --git a/lang/python35/Makefile b/lang/python35/Makefile
index 981b9a5f8118..fe6fe01dfb61 100644
--- a/lang/python35/Makefile
+++ b/lang/python35/Makefile
@@ -3,7 +3,7 @@
 
 PORTNAME=	python
 PORTVERSION=	${PYTHON_PORTVERSION}
-PORTREVISION=	2
+PORTREVISION=	3
 CATEGORIES=	lang python
 MASTER_SITES=	PYTHON/ftp/python/${PORTVERSION}
 PKGNAMESUFFIX=	${PYTHON_SUFFIX}
diff --git a/lang/python35/files/patch-Modules___posixsubprocess.c b/lang/python35/files/patch-Modules___posixsubprocess.c
new file mode 100644
index 000000000000..54e31f476b3b
--- /dev/null
+++ b/lang/python35/files/patch-Modules___posixsubprocess.c
@@ -0,0 +1,25 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/_posixsubprocess.c.orig	2019-11-01 23:02:34 UTC
++++ Modules/_posixsubprocess.c
+@@ -233,8 +233,15 @@ _close_fds_by_brute_force(long start_fd, PyObject *py_
+         start_fd = keep_fd + 1;
+     }
+     if (start_fd <= end_fd) {
+-        for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
+-            close(fd_num);
++#ifdef __FreeBSD__
++        if (end_fd >= sysconf(_SC_OPEN_MAX)) {
++            closefrom(start_fd);
++        } else
++#endif
++        {
++            for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
++                close(fd_num);
++            }
+         }
+     }
+ }
diff --git a/lang/python35/files/patch-Modules_posixmodule.c b/lang/python35/files/patch-Modules_posixmodule.c
new file mode 100644
index 000000000000..169075797556
--- /dev/null
+++ b/lang/python35/files/patch-Modules_posixmodule.c
@@ -0,0 +1,27 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/posixmodule.c.orig	2019-11-01 23:02:34 UTC
++++ Modules/posixmodule.c
+@@ -7853,9 +7853,16 @@ os_closerange_impl(PyObject *module, int fd_low, int f
+     int i;
+     Py_BEGIN_ALLOW_THREADS
+     _Py_BEGIN_SUPPRESS_IPH
+-    for (i = fd_low; i < fd_high; i++)
+-        if (_PyVerify_fd(i))
+-            close(i);
++#ifdef __FreeBSD__
++    if (fd_high >= sysconf(_SC_OPEN_MAX)) {
++        closefrom(fd_low);
++    } else
++#endif
++    {
++        for (i = fd_low; i < fd_high; i++)
++            if (_PyVerify_fd(i))
++                close(i);
++    }
+     _Py_END_SUPPRESS_IPH
+     Py_END_ALLOW_THREADS
+     Py_RETURN_NONE;
diff --git a/lang/python36/Makefile b/lang/python36/Makefile
index 81c827a9994a..0ec8d034230e 100644
--- a/lang/python36/Makefile
+++ b/lang/python36/Makefile
@@ -3,6 +3,7 @@
 
 PORTNAME=	python
 PORTVERSION=	${PYTHON_PORTVERSION}
+PORTREVISION=	1
 CATEGORIES=	lang python
 MASTER_SITES=	PYTHON/ftp/python/${PORTVERSION}
 PKGNAMESUFFIX=	${PYTHON_SUFFIX}
diff --git a/lang/python36/files/patch-Modules___posixsubprocess.c b/lang/python36/files/patch-Modules___posixsubprocess.c
new file mode 100644
index 000000000000..01542ecb9e85
--- /dev/null
+++ b/lang/python36/files/patch-Modules___posixsubprocess.c
@@ -0,0 +1,25 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/_posixsubprocess.c.orig	2019-07-02 20:25:39 UTC
++++ Modules/_posixsubprocess.c
+@@ -236,8 +236,15 @@ _close_fds_by_brute_force(long start_fd, PyObject *py_
+         start_fd = keep_fd + 1;
+     }
+     if (start_fd <= end_fd) {
+-        for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
+-            close(fd_num);
++#ifdef __FreeBSD__
++        if (end_fd >= sysconf(_SC_OPEN_MAX)) {
++            closefrom(start_fd);
++        } else
++#endif
++        {
++            for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
++                close(fd_num);
++            }
+         }
+     }
+ }
diff --git a/lang/python36/files/patch-Modules_posixmodule.c b/lang/python36/files/patch-Modules_posixmodule.c
new file mode 100644
index 000000000000..a0247dcc628d
--- /dev/null
+++ b/lang/python36/files/patch-Modules_posixmodule.c
@@ -0,0 +1,26 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/posixmodule.c.orig	2019-07-02 20:25:39 UTC
++++ Modules/posixmodule.c
+@@ -7685,8 +7685,16 @@ os_closerange_impl(PyObject *module, int fd_low, int f
+     int i;
+     Py_BEGIN_ALLOW_THREADS
+     _Py_BEGIN_SUPPRESS_IPH
+-    for (i = Py_MAX(fd_low, 0); i < fd_high; i++)
+-        close(i);
++    fd_low = Py_MAX(fd_low, 0);
++#ifdef __FreeBSD__
++    if (fd_high >= sysconf(_SC_OPEN_MAX)) {
++        closefrom(fd_low);
++    } else
++#endif
++    {
++        for (i = fd_low; i < fd_high; i++)
++            close(i);
++    }
+     _Py_END_SUPPRESS_IPH
+     Py_END_ALLOW_THREADS
+     Py_RETURN_NONE;
diff --git a/lang/python37/Makefile b/lang/python37/Makefile
index 8d67478e446d..6d56e367d1fc 100644
--- a/lang/python37/Makefile
+++ b/lang/python37/Makefile
@@ -3,6 +3,7 @@
 
 PORTNAME=	python
 PORTVERSION=	${PYTHON_PORTVERSION}
+PORTREVISION=	1
 CATEGORIES=	lang python
 MASTER_SITES=	PYTHON/ftp/python/${PORTVERSION}
 PKGNAMESUFFIX=	${PYTHON_SUFFIX}
diff --git a/lang/python37/files/patch-Modules___posixsubprocess.c b/lang/python37/files/patch-Modules___posixsubprocess.c
new file mode 100644
index 000000000000..f46b682378bd
--- /dev/null
+++ b/lang/python37/files/patch-Modules___posixsubprocess.c
@@ -0,0 +1,25 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/_posixsubprocess.c.orig	2019-10-14 22:32:36 UTC
++++ Modules/_posixsubprocess.c
+@@ -236,8 +236,15 @@ _close_fds_by_brute_force(long start_fd, PyObject *py_
+         start_fd = keep_fd + 1;
+     }
+     if (start_fd <= end_fd) {
+-        for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
+-            close(fd_num);
++#ifdef __FreeBSD__
++        if (end_fd >= sysconf(_SC_OPEN_MAX)) {
++            closefrom(start_fd);
++        } else
++#endif
++        {
++            for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
++                close(fd_num);
++            }
+         }
+     }
+ }
diff --git a/lang/python37/files/patch-Modules_posixmodule.c b/lang/python37/files/patch-Modules_posixmodule.c
new file mode 100644
index 000000000000..28411c3126dd
--- /dev/null
+++ b/lang/python37/files/patch-Modules_posixmodule.c
@@ -0,0 +1,26 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/posixmodule.c.orig	2019-10-14 22:32:36 UTC
++++ Modules/posixmodule.c
+@@ -7810,8 +7810,16 @@ os_closerange_impl(PyObject *module, int fd_low, int f
+     int i;
+     Py_BEGIN_ALLOW_THREADS
+     _Py_BEGIN_SUPPRESS_IPH
+-    for (i = Py_MAX(fd_low, 0); i < fd_high; i++)
+-        close(i);
++    fd_low = Py_MAX(fd_low, 0);
++#ifdef __FreeBSD__
++    if (fd_high >= sysconf(_SC_OPEN_MAX)) {
++        closefrom(fd_low);
++    } else
++#endif
++    {
++        for (i = fd_low; i < fd_high; i++)
++            close(i);
++    }
+     _Py_END_SUPPRESS_IPH
+     Py_END_ALLOW_THREADS
+     Py_RETURN_NONE;
diff --git a/lang/python38/Makefile b/lang/python38/Makefile
index 825d2876f164..20383781a1cc 100644
--- a/lang/python38/Makefile
+++ b/lang/python38/Makefile
@@ -3,7 +3,7 @@
 
 PORTNAME=	python
 PORTVERSION=	${PYTHON_PORTVERSION}
-PORTREVISION=	1
+PORTREVISION=	2
 CATEGORIES=	lang python
 MASTER_SITES=	PYTHON/ftp/python/${PORTVERSION}
 PKGNAMESUFFIX=	${PYTHON_SUFFIX}
diff --git a/lang/python38/files/patch-Modules___posixsubprocess.c b/lang/python38/files/patch-Modules___posixsubprocess.c
new file mode 100644
index 000000000000..a7c4e43e81cf
--- /dev/null
+++ b/lang/python38/files/patch-Modules___posixsubprocess.c
@@ -0,0 +1,25 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/_posixsubprocess.c.orig	2019-10-14 13:34:47 UTC
++++ Modules/_posixsubprocess.c
+@@ -236,8 +236,15 @@ _close_fds_by_brute_force(long start_fd, PyObject *py_
+         start_fd = keep_fd + 1;
+     }
+     if (start_fd <= end_fd) {
+-        for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
+-            close(fd_num);
++#if defined(__FreeBSD__)
++        if (end_fd >= sysconf(_SC_OPEN_MAX)) {
++            closefrom(start_fd);
++        } else
++#endif
++        {
++            for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
++                close(fd_num);
++            }
+         }
+     }
+ }
diff --git a/lang/python38/files/patch-Modules_posixmodule.c b/lang/python38/files/patch-Modules_posixmodule.c
new file mode 100644
index 000000000000..441c78f81016
--- /dev/null
+++ b/lang/python38/files/patch-Modules_posixmodule.c
@@ -0,0 +1,26 @@
+# Add closefrom(2) support
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274
+# https://bugs.python.org/issue38061
+# TODO: Upstream
+
+--- Modules/posixmodule.c.orig	2019-10-14 13:34:47 UTC
++++ Modules/posixmodule.c
+@@ -8460,8 +8460,16 @@ os_closerange_impl(PyObject *module, int fd_low, int f
+     lohi[1] = fd_high;
+     fdwalk(_fdwalk_close_func, lohi);
+ #else
+-    for (i = Py_MAX(fd_low, 0); i < fd_high; i++)
+-        close(i);
++    fd_low = Py_MAX(fd_low, 0);
++#ifdef __FreeBSD__
++    if (fd_high >= sysconf(_SC_OPEN_MAX)) {
++        closefrom(fd_low);
++    } else
++#endif
++    {
++        for (i = fd_low; i < fd_high; i++)
++            close(i);
++    }
+ #endif
+     _Py_END_SUPPRESS_IPH
+     Py_END_ALLOW_THREADS