Sleep for longer at a time in lock_path.

When lock_path is called and the lock goes for the whole 10 seconds,
the flock is called 1000 times. With this patch, the short 0.01 sleep
is used for the first 1% of the total lock time and then 1% of the
total lock time is used.

Change-Id: Ibed6bdb49bddcdb868742c41f86d2482a7edfd29

swift/common/utils.py

@@ -1600,6 +1600,10 @@ def lock_path(directory, timeout=10, timeout_class=None):
     mkdirs(directory)
     lockpath = '%s/.lock' % directory
     fd = os.open(lockpath, os.O_WRONLY | os.O_CREAT)
+    sleep_time = 0.01
+    slower_sleep_time = max(timeout * 0.01, sleep_time)
+    slowdown_at = timeout * 0.01
+    time_slept = 0
     try:
         with timeout_class(timeout, lockpath):
             while True:
@@ -1609,7 +1613,10 @@ def lock_path(directory, timeout=10, timeout_class=None):
                 except IOError as err:
                     if err.errno != errno.EAGAIN:
                         raise
-                sleep(0.01)
+                if time_slept > slowdown_at:
+                    sleep_time = slower_sleep_time
+                sleep(sleep_time)
+                time_slept += sleep_time
         yield True
     finally:
         os.close(fd)

test/unit/common/test_utils.py

@@ -727,6 +727,30 @@ class TestUtils(unittest.TestCase):
         finally:
             shutil.rmtree(tmpdir)
 
+    def test_lock_path_num_sleeps(self):
+        tmpdir = mkdtemp()
+        num_short_calls = [0]
+        exception_raised = [False]
+
+        def my_sleep(to_sleep):
+            if to_sleep == 0.01:
+                num_short_calls[0] += 1
+            else:
+                raise Exception('sleep time changed: %s' % to_sleep)
+
+        try:
+            with mock.patch('swift.common.utils.sleep', my_sleep):
+                with utils.lock_path(tmpdir):
+                    with utils.lock_path(tmpdir):
+                        pass
+        except Exception as e:
+            exception_raised[0] = True
+            self.assertTrue('sleep time changed' in str(e))
+        finally:
+            shutil.rmtree(tmpdir)
+        self.assertEqual(num_short_calls[0], 11)
+        self.assertTrue(exception_raised[0])
+
     def test_lock_path_class(self):
         tmpdir = mkdtemp()
         try: