closes bpo-32859: Don't retry dup3() if it is not available at runtime (GH-5708)

miss-islington · izbyshev · benjaminp · commit 16de2a9b8697 · 2018-02-20T21:21:12.000-08:00
os.dup2() tests for dup3() system call availability at runtime, but doesn't remember the result across calls, repeating the test on each call with inheritable=False. Since the caller of os.dup2() is expected to hold the GIL, fix this by making the variable holding the test result static. (cherry picked from commit b3caf38) Co-authored-by: Alexey Izbyshev <izbyshev@users.noreply.github.com>
diff --git a/Misc/NEWS.d/next/Library/2018-02-19-17-46-31.bpo-32859.kAT-Xp.rst b/Misc/NEWS.d/next/Library/2018-02-19-17-46-31.bpo-32859.kAT-Xp.rst
@@ -0,0 +1,2 @@
+In ``os.dup2``, don't check every call whether the ``dup3`` syscall exists
+or not.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
@@ -7704,7 +7704,7 @@ os_dup2_impl(PyObject *module, int fd, int fd2, int inheritable)
 #if defined(HAVE_DUP3) && \
     !(defined(HAVE_FCNTL_H) && defined(F_DUP2FD_CLOEXEC))
     /* dup3() is available on Linux 2.6.27+ and glibc 2.9 */
-    int dup3_works = -1;
+    static int dup3_works = -1;
 #endif
 
     if (fd < 0 || fd2 < 0)

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+In ``os.dup2``, don't check every call whether the ``dup3`` syscall exists
	`2`	`+or not.`