Issue #1731717: Fixed the problem where subprocess.wait() could cause an

OSError exception when The OS had been told to ignore SIGCLD in our process
or otherwise not wait for exiting child processes.

Lib/subprocess.py

@@ -1295,7 +1295,11 @@ class Popen(object):
                 os.close(errpipe_read)
 
             if data:
-                _eintr_retry_call(os.waitpid, self.pid, 0)
+                try:
+                    _eintr_retry_call(os.waitpid, self.pid, 0)
+                except OSError as e:
+                    if e.errno != errno.ECHILD:
+                        raise
                 try:
                     exception_name, hex_errno, err_msg = data.split(b':', 2)
                 except ValueError:
@@ -1358,7 +1362,15 @@ class Popen(object):
             """Wait for child process to terminate.  Returns returncode
             attribute."""
             if self.returncode is None:
-                pid, sts = _eintr_retry_call(os.waitpid, self.pid, 0)
+                try:
+                    pid, sts = _eintr_retry_call(os.waitpid, self.pid, 0)
+                except OSError as e:
+                    if e.errno != errno.ECHILD:
+                        raise
+                    # This happens if SIGCLD is set to be ignored or waiting
+                    # for child processes has otherwise been disabled for our
+                    # process.  This child is dead, we can't get the status.
+                    sts = 0
                 self._handle_exitstatus(sts)
             return self.returncode
 

Lib/test/subprocessdata/sigchild_ignore.py

+import signal, subprocess, sys
+# On Linux this causes os.waitpid to fail with OSError as the OS has already
+# reaped our child process.  The wait() passing the OSError on to the caller
+# and causing us to exit with an error is what we are testing against.
+signal.signal(signal.SIGCLD, signal.SIG_IGN)
+subprocess.Popen([sys.executable, '-c', 'print("albatross")']).wait()

Lib/test/test_subprocess.py

@@ -1073,6 +1073,16 @@ class POSIXProcessTestCase(BaseTestCase):
                         close_fds=False, pass_fds=(fd, )))
             self.assertIn('overriding close_fds', str(context.warning))
 
+    def test_wait_when_sigchild_ignored(self):
+        # NOTE: sigchild_ignore.py may not be an effective test on all OSes.
+        sigchild_ignore = support.findfile("sigchild_ignore.py",
+                                           subdir="subprocessdata")
+        p = subprocess.Popen([sys.executable, sigchild_ignore],
+                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+        stdout, stderr = p.communicate()
+        self.assertEqual(0, p.returncode, "sigchild_ignore.py exited"
+                         " non-zero with this error:\n%s" % stderr)
+
 
 @unittest.skipUnless(mswindows, "Windows specific tests")
 class Win32ProcessTestCase(BaseTestCase):

Misc/NEWS

@@ -33,6 +33,10 @@ Library
   added in 3.2beta1) to allow specifying a specific list of file descriptors
   to keep open in the child process.
 
+- Issue #1731717: Fixed the problem where subprocess.wait() could cause an
+  OSError exception when The OS had been told to ignore SIGCLD in our process
+  or otherwise not wait for exiting child processes.
+
 
 What's New in Python 3.2 Beta 1?
 ================================