Issue #25654:

* multiprocessing: open file with closefd=False to avoid ResourceWarning
* _test_multiprocessing: open file with O_EXCL to detect bugs in tests (if a
  previous test forgot to remove TESTFN)
* test_sys_exit(): remove TESTFN after each loop iteration

Initial patch written by Serhiy Storchaka.

3 files changed, 25 insertions, 13 deletions

diff --git a/Lib/multiprocessing/forkserver.py b/Lib/multiprocessing/forkserver.py
index b27cba5..ad01ede 100644
--- a/Lib/multiprocessing/forkserver.py
+++ b/Lib/multiprocessing/forkserver.py
@@ -147,13 +147,7 @@ def main(listener_fd, alive_r, preload, main_path=None, sys_path=None):
             except ImportError:
                 pass
 
-    # close sys.stdin
-    if sys.stdin is not None:
-        try:
-            sys.stdin.close()
-            sys.stdin = open(os.devnull)
-        except (OSError, ValueError):
-            pass
+    util._close_stdin()
 
     # ignoring SIGCHLD means no need to reap zombie processes
     handler = signal.signal(signal.SIGCHLD, signal.SIG_IGN)
diff --git a/Lib/multiprocessing/process.py b/Lib/multiprocessing/process.py
index 68959bf..bca8b7a 100644
--- a/Lib/multiprocessing/process.py
+++ b/Lib/multiprocessing/process.py
@@ -234,12 +234,7 @@ class BaseProcess(object):
                 context._force_start_method(self._start_method)
             _process_counter = itertools.count(1)
             _children = set()
-            if sys.stdin is not None:
-                try:
-                    sys.stdin.close()
-                    sys.stdin = open(os.devnull)
-                except (OSError, ValueError):
-                    pass
+            util._close_stdin()
             old_process = _current_process
             _current_process = self
             try:
diff --git a/Lib/multiprocessing/util.py b/Lib/multiprocessing/util.py
index ea5443d..1a2c0db 100644
--- a/Lib/multiprocessing/util.py
+++ b/Lib/multiprocessing/util.py
@@ -9,6 +9,7 @@
 
 import os
 import itertools
+import sys
 import weakref
 import atexit
 import threading        # we want threading to install it's
@@ -356,6 +357,28 @@ def close_all_fds_except(fds):
     assert fds[-1] == MAXFD, 'fd too large'
     for i in range(len(fds) - 1):
         os.closerange(fds[i]+1, fds[i+1])
+#
+# Close sys.stdin and replace stdin with os.devnull
+#
+
+def _close_stdin():
+    if sys.stdin is None:
+        return
+
+    try:
+        sys.stdin.close()
+    except (OSError, ValueError):
+        pass
+
+    try:
+        fd = os.open(os.devnull, os.O_RDONLY)
+        try:
+            sys.stdin = open(fd, closefd=False)
+        except:
+            os.close(fd)
+            raise
+    except (OSError, ValueError):
+        pass
 
 #
 # Start a program with only specified fds kept open