commit 449b27179931aa570597556ed4865ac2f1f981c9
author Victor Stinner <victor.stinner@gmail.com> Tue Sep 29 13:59:50 2015 +0200
committer Victor Stinner <victor.stinner@gmail.com> Tue Sep 29 13:59:50 2015 +0200
tree 1d490e256eb029d67e2cee1a2514a4633f5ca53f
parent 3f7468507ae83d66cee059fb8e51692d8adb797b

Issue #18174: Explain why is_valid_fd() uses dup() instead of fstat()

Python/pylifecycle.c

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 4f5efc9..857a543 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -972,6 +972,9 @@
     if (fd < 0 || !_PyVerify_fd(fd))
         return 0;
     _Py_BEGIN_SUPPRESS_IPH
+    /* Prefer dup() over fstat(). fstat() can require input/output whereas
+       dup() doesn't, there is a low risk of EMFILE/ENFILE at Python
+       startup. */
     fd2 = dup(fd);
     if (fd2 >= 0)
         close(fd2);