From 3ed9455ec10bd03299d510301b25f36968476f96 Mon Sep 17 00:00:00 2001
From: Victor Stinner <victor.stinner@gmail.com>
Date: Tue, 29 Sep 2015 13:59:50 +0200
Subject: Issue #18174: Explain why is_valid_fd() uses dup() instead of fstat()

---
 Python/pylifecycle.c | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'Python')

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 4f5efc963c..857a543cf5 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -972,6 +972,9 @@ is_valid_fd(int fd)
     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);
-- 
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