Index: Lib/popen2.py
===================================================================
--- Lib/popen2.py	(revision 43241)
+++ Lib/popen2.py	(working copy)
@@ -8,6 +8,7 @@
 
 import os
 import sys
+import errno
 
 __all__ = ["popen2", "popen3", "popen4"]
 
@@ -75,26 +76,36 @@
         finally:
             os._exit(1)
 
+    def _wait_on_pid(self, flag):
+        try:
+            pid, sts = os.waitpid(self.pid, flag)
+            child_is_dead = pid == self.pid
+        except os.error, e:
+            # If the child no longer exists, it must have been waited on
+            # by someone else.  We don't know what the status is,
+            # but we want to stop polling, so set to zero.
+            sts = 0
+            child_is_dead = e.errno == errno.ECHILD
+
+        if child_is_dead:
+            self.sts = sts
+            try:
+                _active.remove(self)
+            except ValueError:
+                # We must have been removed by another thread, just ignore.
+                pass
+
     def poll(self):
         """Return the exit status of the child process if it has finished,
         or -1 if it hasn't finished yet."""
         if self.sts < 0:
-            try:
-                pid, sts = os.waitpid(self.pid, os.WNOHANG)
-                if pid == self.pid:
-                    self.sts = sts
-                    _active.remove(self)
-            except os.error:
-                pass
+            self._wait_on_pid(os.WNOHANG)
         return self.sts
 
     def wait(self):
         """Wait for and return the exit status of the child process."""
         if self.sts < 0:
-            pid, sts = os.waitpid(self.pid, 0)
-            if pid == self.pid:
-                self.sts = sts
-                _active.remove(self)
+            self._wait_on_pid(0)
         return self.sts