bpo-45915: use fcntl(fd, F_GETFD) in is_valid_fd() (GH-29821)
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-11-28-11-25-08.bpo-45915.TSGcLF.rst b/Misc/NEWS.d/next/Core and Builtins/2021-11-28-11-25-08.bpo-45915.TSGcLF.rst
new file mode 100644
index 0000000..aa268f4
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-11-28-11-25-08.bpo-45915.TSGcLF.rst
@@ -0,0 +1 @@
+``is_valid_fd`` now uses faster ``fcntl(fd, F_GETFD)`` on Linux, macOS, and Windows.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 7e6060e..74d269b 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -30,6 +30,10 @@
# include <langinfo.h> // nl_langinfo(CODESET)
#endif
+#ifdef HAVE_FCNTL_H
+# include <fcntl.h> // F_GETFD
+#endif
+
#ifdef MS_WINDOWS
# undef BYTE
# 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
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
side of the pipe is closed, dup(1) succeed, whereas fstat(1, &st) fails with
EBADF. FreeBSD has similar issue (bpo-32849).
Only use dup() on platforms where dup() is enough to detect invalid FD in
- corner cases: on Linux and Windows (bpo-32849). */
-#if defined(__linux__) || defined(MS_WINDOWS)
+ corner cases: on Linux and Windows (bpo-32849).
+*/
if (fd < 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;
-
_Py_BEGIN_SUPPRESS_IPH
fd2 = dup(fd);
if (fd2 >= 0) {
