Eliminate sleep in the lockutils test case (across processes)

Fork many processes and try to lock the same set of files
using flock without blocking and make sure we wait for all the processes
to finish as well.

Fixes LP #1068316

Change-Id: I09964b2c5af63f31b5ddee1f18eaf646f8d8ba58

tests/unit/test_lockutils.py

@@ -15,6 +15,7 @@
 #    under the License.
 
 import errno
+import fcntl
 import os
 import select
 import shutil
@@ -129,39 +130,54 @@ def inner_lock():
             if os.path.exists(tempdir):
                 shutil.rmtree(tempdir)
 
-    @testutils.skip_test("Regularly fails, see bug #1095957")
     def test_synchronized_externally(self):
         """We can lock across multiple processes"""
         tempdir = tempfile.mkdtemp()
         self.config(lock_path=tempdir)
-        rpipe1, wpipe1 = os.pipe()
-        rpipe2, wpipe2 = os.pipe()
-
-        @lockutils.synchronized('testlock1', 'test-', external=True)
-        def f(rpipe, wpipe):
-            try:
-                os.write(wpipe, "foo")
-            except OSError, e:
-                self.assertEquals(e.errno, errno.EPIPE)
-                return
-
-            rfds, _wfds, _efds = select.select([rpipe], [], [], 1)
-            self.assertEquals(len(rfds), 0, "The other process, which was "
-                                            "supposed to be locked, "
-                                            "wrote on its end of the "
-                                            "pipe")
-            os.close(rpipe)
-
-        pid = os.fork()
-        if pid > 0:
-            os.close(wpipe1)
-            os.close(rpipe2)
-
-            f(rpipe1, wpipe2)
-        else:
-            os.close(rpipe1)
-            os.close(wpipe2)
-
-            time.sleep(0.1)
-            f(rpipe2, wpipe1)
-            os._exit(0)
+
+        @lockutils.synchronized('external', 'test-', external=True)
+        def lock_files(tempdir):
+            if not os.path.exists(tempdir):
+                os.makedirs(tempdir)
+
+            # Open some files we can use for locking
+            handles = []
+            for n in range(50):
+                path = os.path.join(tempdir, ('file-%s' % n))
+                handles.append(open(path, 'w'))
+
+            # Loop over all the handles and try locking the file
+            # without blocking, keep a count of how many files we
+            # were able to lock and then unlock. If the lock fails
+            # we get an IOError and bail out with bad exit code
+            count = 0
+            for handle in handles:
+                try:
+                    fcntl.flock(handle, fcntl.LOCK_EX | fcntl.LOCK_NB)
+                    count += 1
+                    fcntl.flock(handle, fcntl.LOCK_UN)
+                except IOError:
+                    os._exit(2)
+                finally:
+                    handle.close()
+
+            # Check if we were able to open all files
+            self.assertEqual(50, count)
+
+        try:
+            children = []
+            for n in range(50):
+                pid = os.fork()
+                if pid:
+                    children.append(pid)
+                else:
+                    lock_files(tempdir)
+                    os._exit(0)
+
+            for i, child in enumerate(children):
+                (pid, status) = os.waitpid(child, 0)
+                if pid:
+                    self.assertEqual(0, status)
+        finally:
+            if os.path.exists(tempdir):
+                shutil.rmtree(tempdir, ignore_errors=True)