diff -r 03063e718f5f Lib/multiprocessing/connection.py
--- a/Lib/multiprocessing/connection.py	Mon Jul 23 10:22:36 2012 -0500
+++ b/Lib/multiprocessing/connection.py	Tue Jul 24 09:37:13 2012 -0400
@@ -497,6 +497,11 @@
         '''
         if duplex:
             s1, s2 = socket.socketpair()
+            # _multiprocessing.Connection read/write semantics do not handle
+            # non-blocking sockets correctly (issue 6056). This bug-fix
+            # retains current behavior and allows for socket default timeout
+            s1.setblocking(True)
+            s2.setblocking(True)
             c1 = Connection(s1.detach())
             c2 = Connection(s2.detach())
         else:
@@ -561,6 +566,8 @@
             if os.name == 'posix':
                 self._socket.setsockopt(socket.SOL_SOCKET,
                                         socket.SO_REUSEADDR, 1)
+            # blocking sockets fix for issue 6056
+            self._socket.setblocking(True)
             self._socket.bind(address)
             self._socket.listen(backlog)
             self._address = self._socket.getsockname()
@@ -579,6 +586,8 @@
 
     def accept(self):
         s, self._last_accepted = self._socket.accept()
+        # blocking sockets fix for issue 6056
+        s.setblocking(True)
         return Connection(s.detach())
 
     def close(self):
@@ -593,6 +602,8 @@
     '''
     family = address_type(address)
     with socket.socket( getattr(socket, family) ) as s:
+        # blocking sockets fix for issue 6056
+        s.setblocking(True)
         s.connect(address)
         return Connection(s.detach())
 
diff -r 03063e718f5f Lib/test/test_multiprocessing.py
--- a/Lib/test/test_multiprocessing.py	Mon Jul 23 10:22:36 2012 -0500
+++ b/Lib/test/test_multiprocessing.py	Tue Jul 24 09:37:13 2012 -0400
@@ -3317,43 +3317,18 @@
                    TestFlags]
 
 #
+# Issue 6056: test with/without non-blocking sockets
 #
-#
-
-def test_main(run=None):
-    if sys.platform.startswith("linux"):
-        try:
-            lock = multiprocessing.RLock()
-        except OSError:
-            raise unittest.SkipTest("OSError raises on RLock creation, see issue 3111!")
-
-    check_enough_semaphores()
-
-    if run is None:
-        from test.support import run_unittest as run
-
-    util.get_temp_dir()     # creates temp directory for use by all processes
-
-    multiprocessing.get_logger().setLevel(LOG_LEVEL)
-
-    ProcessesMixin.pool = multiprocessing.Pool(4)
-    ThreadsMixin.pool = multiprocessing.dummy.Pool(4)
-    ManagerMixin.manager.__init__()
-    ManagerMixin.manager.start()
-    ManagerMixin.pool = ManagerMixin.manager.Pool(4)
-
-    testcases = (
-        sorted(testcases_processes.values(), key=lambda tc:tc.__name__) +
-        sorted(testcases_threads.values(), key=lambda tc:tc.__name__) +
-        sorted(testcases_manager.values(), key=lambda tc:tc.__name__) +
-        testcases_other
-        )
-
-    loadTestsFromTestCase = unittest.defaultTestLoader.loadTestsFromTestCase
-    suite = unittest.TestSuite(loadTestsFromTestCase(tc) for tc in testcases)
-    try:
-        run(suite)
-    finally:
+
+class MultiprocessingTestSuite( unittest.TestSuite ):
+    def setUp(self):
+        ProcessesMixin.pool = multiprocessing.Pool(4)
+        ThreadsMixin.pool = multiprocessing.dummy.Pool(4)
+        ManagerMixin.manager.__init__()
+        ManagerMixin.manager.start()
+        ManagerMixin.pool = ManagerMixin.manager.Pool(4)
+
+    def tearDown(self):
         ThreadsMixin.pool.terminate()
         ProcessesMixin.pool.terminate()
         ManagerMixin.pool.terminate()
@@ -3364,6 +3339,57 @@
         ProcessesMixin.pool.join()
         del ProcessesMixin.pool, ThreadsMixin.pool, ManagerMixin.pool
 
+    def run( self, result, debug=False ):
+        self.setUp()
+        try:
+            super().run( result, debug )
+        finally:
+            self.tearDown() 
+
+class NonBlockingSocketSuite( MultiprocessingTestSuite ):
+    def setUp(self):
+        socket.setdefaulttimeout(30)
+        super().setUp()
+
+    def tearDown(self):
+        super().tearDown()
+        socket.setdefaulttimeout(None)
+
+#
+#
+#
+
+def test_main(run=None):
+    if sys.platform.startswith("linux"):
+        try:
+            lock = multiprocessing.RLock()
+        except OSError:
+            raise unittest.SkipTest("OSError raises on RLock creation, see issue 3111!")
+
+    check_enough_semaphores()
+
+    if run is None:
+        from test.support import run_unittest as run
+
+    util.get_temp_dir()     # creates temp directory for use by all processes
+
+    multiprocessing.get_logger().setLevel(LOG_LEVEL)
+
+    testcases = (
+        sorted(testcases_processes.values(), key=lambda tc:tc.__name__) +
+        sorted(testcases_threads.values(), key=lambda tc:tc.__name__) +
+        sorted(testcases_manager.values(), key=lambda tc:tc.__name__) +
+        testcases_other
+        )
+
+    loadTestsFromTestCase = unittest.defaultTestLoader.loadTestsFromTestCase
+    suiteBlocking = MultiprocessingTestSuite(loadTestsFromTestCase(tc) for tc in testcases)
+    suiteNonBlocking = NonBlockingSocketSuite(loadTestsFromTestCase(tc) for tc in testcases)
+
+    suite = unittest.TestSuite([suiteBlocking,suiteNonBlocking])
+
+    run(suite)
+
 def main():
     test_main(unittest.TextTestRunner(verbosity=2).run)
 
diff -r 03063e718f5f Misc/ACKS
--- a/Misc/ACKS	Mon Jul 23 10:22:36 2012 -0500
+++ b/Misc/ACKS	Tue Jul 24 09:37:13 2012 -0400
@@ -1130,6 +1130,7 @@
 Sue Williams
 Frank Willison
 Greg V. Wilson
+J Derek Wilson
 Jody Winston
 Collin Winter
 Dik Winter
diff -r 03063e718f5f Misc/NEWS
--- a/Misc/NEWS	Mon Jul 23 10:22:36 2012 -0500
+++ b/Misc/NEWS	Tue Jul 24 09:37:13 2012 -0400
@@ -52,6 +52,9 @@
 Library
 -------
 
+- Issue #6056: Allow socket.setdefaulttimeout to work with _mutliprocessing
+  C-API socket interface that expects blocking sockets.
+
 - Issue #15402: An issue in the struct module that caused sys.getsizeof to
   return incorrect results for struct.Struct instances has been fixed.
   Initial patch by Serhiy Storchaka.