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bpo-45915: use fcntl(fd, F_GETFD) in is_valid_fd() (GH-29821)

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Christian Heimes 2021-11-28 20:40:27 +02:00 • committed by GitHub
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commit f87ea03502
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2 changed files with 16 additions and 3 deletions
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1
Misc/NEWS.d/next/Core and Builtins/2021-11-28-11-25-08.bpo-45915.TSGcLF.rst Normal file
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@ -0,0 +1 @@
``is_valid_fd`` now uses faster ``fcntl(fd, F_GETFD)`` on Linux, macOS, and Windows.

18
Python/pylifecycle.c
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@ -30,6 +30,10 @@
# include <langinfo.h> // nl_langinfo(CODESET) # include <langinfo.h> // nl_langinfo(CODESET)
#endif #endif
#ifdef HAVE_FCNTL_H
# include <fcntl.h> // F_GETFD
#endif
#ifdef MS_WINDOWS #ifdef MS_WINDOWS
# undef BYTE # undef BYTE
# include "windows.h" # include "windows.h"
@ -2129,18 +2133,26 @@ is_valid_fd(int fd)
startup. Problem: dup() doesn't check if the file descriptor is valid on startup. Problem: dup() doesn't check if the file descriptor is valid on
some platforms. some platforms.
fcntl(fd, F_GETFD) is even faster, because it only checks the process table.
bpo-30225: On macOS Tiger, when stdout is redirected to a pipe and the other bpo-30225: On macOS Tiger, when stdout is redirected to a pipe and the other
side of the pipe is closed, dup(1) succeed, whereas fstat(1, &st) fails with side of the pipe is closed, dup(1) succeed, whereas fstat(1, &st) fails with
EBADF. FreeBSD has similar issue (bpo-32849). EBADF. FreeBSD has similar issue (bpo-32849).
Only use dup() on platforms where dup() is enough to detect invalid FD in Only use dup() on platforms where dup() is enough to detect invalid FD in
corner cases: on Linux and Windows (bpo-32849). */ corner cases: on Linux and Windows (bpo-32849).
#if defined(__linux__) || defined(MS_WINDOWS) */
if (fd < 0) { if (fd < 0) {
return 0; return 0;
} }
#if defined(F_GETFD) && (defined(__linux__) || defined(__APPLE__) || defined(MS_WINDOWS))
int res;
_Py_BEGIN_SUPPRESS_IPH
res = fcntl(fd, F_GETFD);
_Py_END_SUPPRESS_IPH
return res >= 0;
#elif defined(__linux__) || defined(MS_WINDOWS)
int fd2; int fd2;
_Py_BEGIN_SUPPRESS_IPH _Py_BEGIN_SUPPRESS_IPH
fd2 = dup(fd); fd2 = dup(fd);
if (fd2 >= 0) { if (fd2 >= 0) {