[Python-checkins] gh-92301: subprocess: Prefer close_range() to procfs-based fd closing (#92303)
gpshead
webhook-mailer at python.org
Thu May 5 12:46:24 EDT 2022
https://github.com/python/cpython/commit/58573ffba0e4d3c7d6e6712169578e45d2926dbd
commit: 58573ffba0e4d3c7d6e6712169578e45d2926dbd
branch: main
author: Alexey Izbyshev <izbyshev at ispras.ru>
committer: gpshead <greg at krypto.org>
date: 2022-05-05T09:46:19-07:00
summary:
gh-92301: subprocess: Prefer close_range() to procfs-based fd closing (#92303)
#92301: subprocess: Prefer `close_range()` to procfs-based fd closing.
`close_range()` is much faster for large number of file descriptors, e.g.
4 times faster for 1000 descriptors in a Linux 5.16-based environment.
We prefer close_range() only if it's known to be async-signal-safe.
files:
A Misc/NEWS.d/next/Library/2022-05-04-11-54-37.gh-issue-92301.eqjoYX.rst
M Modules/_posixsubprocess.c
diff --git a/Misc/NEWS.d/next/Library/2022-05-04-11-54-37.gh-issue-92301.eqjoYX.rst b/Misc/NEWS.d/next/Library/2022-05-04-11-54-37.gh-issue-92301.eqjoYX.rst
new file mode 100644
index 0000000000000..b0b0502bf0a75
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-05-04-11-54-37.gh-issue-92301.eqjoYX.rst
@@ -0,0 +1,2 @@
+Prefer ``close_range()`` to iterating over procfs for file descriptor
+closing in :mod:`subprocess` for better performance.
diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index 2440609e31bcc..21c2bd13a3e27 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -210,18 +210,23 @@ safe_get_max_fd(void)
}
-/* Close all file descriptors in the range from start_fd and higher
- * except for those in py_fds_to_keep. If the range defined by
- * [start_fd, safe_get_max_fd()) is large this will take a long
- * time as it calls close() on EVERY possible fd.
+/* Close all file descriptors in the given range except for those in
+ * py_fds_to_keep by invoking closer on each subrange.
*
- * It isn't possible to know for sure what the max fd to go up to
- * is for processes with the capability of raising their maximum.
+ * If end_fd == -1, it's guessed via safe_get_max_fd(), but it isn't
+ * possible to know for sure what the max fd to go up to is for
+ * processes with the capability of raising their maximum, or in case
+ * a process opened a high fd and then lowered its maximum.
*/
-static void
-_close_fds_by_brute_force(long start_fd, PyObject *py_fds_to_keep)
+static int
+_close_range_except(int start_fd,
+ int end_fd,
+ PyObject *py_fds_to_keep,
+ int (*closer)(int, int))
{
- long end_fd = safe_get_max_fd();
+ if (end_fd == -1) {
+ end_fd = Py_MIN(safe_get_max_fd(), INT_MAX);
+ }
Py_ssize_t num_fds_to_keep = PyTuple_GET_SIZE(py_fds_to_keep);
Py_ssize_t keep_seq_idx;
/* As py_fds_to_keep is sorted we can loop through the list closing
@@ -231,15 +236,17 @@ _close_fds_by_brute_force(long start_fd, PyObject *py_fds_to_keep)
int keep_fd = PyLong_AsLong(py_keep_fd);
if (keep_fd < start_fd)
continue;
- _Py_closerange(start_fd, keep_fd - 1);
+ if (closer(start_fd, keep_fd - 1) != 0)
+ return -1;
start_fd = keep_fd + 1;
}
if (start_fd <= end_fd) {
- _Py_closerange(start_fd, end_fd);
+ if (closer(start_fd, end_fd) != 0)
+ return -1;
}
+ return 0;
}
-
#if defined(__linux__) && defined(HAVE_SYS_SYSCALL_H)
/* It doesn't matter if d_name has room for NAME_MAX chars; we're using this
* only to read a directory of short file descriptor number names. The kernel
@@ -255,6 +262,16 @@ struct linux_dirent64 {
char d_name[256]; /* Filename (null-terminated) */
};
+static int
+_brute_force_closer(int first, int last)
+{
+ for (int i = first; i <= last; i++) {
+ /* Ignore errors */
+ (void)close(i);
+ }
+ return 0;
+}
+
/* Close all open file descriptors in the range from start_fd and higher
* Do not close any in the sorted py_fds_to_keep list.
*
@@ -278,7 +295,7 @@ _close_open_fds_safe(int start_fd, PyObject* py_fds_to_keep)
fd_dir_fd = _Py_open_noraise(FD_DIR, O_RDONLY);
if (fd_dir_fd == -1) {
/* No way to get a list of open fds. */
- _close_fds_by_brute_force(start_fd, py_fds_to_keep);
+ _close_range_except(start_fd, -1, py_fds_to_keep, _brute_force_closer);
return;
} else {
char buffer[sizeof(struct linux_dirent64)];
@@ -306,10 +323,16 @@ _close_open_fds_safe(int start_fd, PyObject* py_fds_to_keep)
}
}
-#define _close_open_fds _close_open_fds_safe
+#define _close_open_fds_fallback _close_open_fds_safe
#else /* NOT (defined(__linux__) && defined(HAVE_SYS_SYSCALL_H)) */
+static int
+_unsafe_closer(int first, int last)
+{
+ _Py_closerange(first, last);
+ return 0;
+}
/* Close all open file descriptors from start_fd and higher.
* Do not close any in the sorted py_fds_to_keep tuple.
@@ -325,7 +348,7 @@ _close_open_fds_safe(int start_fd, PyObject* py_fds_to_keep)
* http://womble.decadent.org.uk/readdir_r-advisory.html
*/
static void
-_close_open_fds_maybe_unsafe(long start_fd, PyObject* py_fds_to_keep)
+_close_open_fds_maybe_unsafe(int start_fd, PyObject* py_fds_to_keep)
{
DIR *proc_fd_dir;
#ifndef HAVE_DIRFD
@@ -348,7 +371,7 @@ _close_open_fds_maybe_unsafe(long start_fd, PyObject* py_fds_to_keep)
proc_fd_dir = opendir(FD_DIR);
if (!proc_fd_dir) {
/* No way to get a list of open fds. */
- _close_fds_by_brute_force(start_fd, py_fds_to_keep);
+ _close_range_except(start_fd, -1, py_fds_to_keep, _unsafe_closer);
} else {
struct dirent *dir_entry;
#ifdef HAVE_DIRFD
@@ -369,16 +392,45 @@ _close_open_fds_maybe_unsafe(long start_fd, PyObject* py_fds_to_keep)
}
if (errno) {
/* readdir error, revert behavior. Highly Unlikely. */
- _close_fds_by_brute_force(start_fd, py_fds_to_keep);
+ _close_range_except(start_fd, -1, py_fds_to_keep, _unsafe_closer);
}
closedir(proc_fd_dir);
}
}
-#define _close_open_fds _close_open_fds_maybe_unsafe
+#define _close_open_fds_fallback _close_open_fds_maybe_unsafe
#endif /* else NOT (defined(__linux__) && defined(HAVE_SYS_SYSCALL_H)) */
+/* We can use close_range() library function only if it's known to be
+ * async-signal-safe.
+ *
+ * On Linux, glibc explicitly documents it to be a thin wrapper over
+ * the system call, and other C libraries are likely to follow glibc.
+ */
+#if defined(HAVE_CLOSE_RANGE) && \
+ (defined(__linux__) || defined(__FreeBSD__))
+#define HAVE_ASYNC_SAFE_CLOSE_RANGE
+
+static int
+_close_range_closer(int first, int last)
+{
+ return close_range(first, last, 0);
+}
+#endif
+
+static void
+_close_open_fds(int start_fd, PyObject* py_fds_to_keep)
+{
+#ifdef HAVE_ASYNC_SAFE_CLOSE_RANGE
+ if (_close_range_except(
+ start_fd, INT_MAX, py_fds_to_keep,
+ _close_range_closer) == 0) {
+ return;
+ }
+#endif
+ _close_open_fds_fallback(start_fd, py_fds_to_keep);
+}
#ifdef VFORK_USABLE
/* Reset dispositions for all signals to SIG_DFL except for ignored
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