From f38b4e71714093d2804c18a963f05e85a75a8ffe Mon Sep 17 00:00:00 2001
From: Scott Gasch <scott@gasch.org>
Date: Sat, 20 Aug 2022 19:06:09 -0700
Subject: [PATCH] Make release return a bool.  Improve tests and logging.

---
 tests/zookeeper_test.py |  8 ++++----
 zookeeper.py            | 34 +++++++++++++++++++++++-----------
 2 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/tests/zookeeper_test.py b/tests/zookeeper_test.py
index 6c00314..05749c1 100644
--- a/tests/zookeeper_test.py
+++ b/tests/zookeeper_test.py
@@ -20,9 +20,9 @@ class TestZookeeper(unittest.TestCase):
     @zookeeper.obtain_lease(also_pass_lease=True, duration=datetime.timedelta(minutes=1))
     def test_release_lease(self, lease: zookeeper.RenewableReleasableLease):
         self.assertTrue(lease)
-        lease.release()
+        self.assertTrue(lease.release())
         self.assertFalse(lease)
-        lease.release()
+        self.assertFalse(lease.release())
         self.assertFalse(lease)
 
     @zookeeper.obtain_lease(also_pass_lease=True, duration=datetime.timedelta(minutes=1))
@@ -30,7 +30,7 @@ class TestZookeeper(unittest.TestCase):
         self.assertTrue(lease)
         self.assertTrue(lease.try_renew(datetime.timedelta(minutes=2)))
         self.assertTrue(lease)
-        lease.release()
+        self.assertTrue(lease.release())
 
     @zookeeper.obtain_lease(
         also_pass_lease=True,
@@ -38,7 +38,7 @@ class TestZookeeper(unittest.TestCase):
     )
     def test_cant_renew_lease_after_released(self, lease: zookeeper.RenewableReleasableLease):
         self.assertTrue(lease)
-        lease.release()
+        self.assertTrue(lease.release())
         self.assertFalse(lease)
         self.assertFalse(lease.try_renew(datetime.timedelta(minutes=2)))
 
diff --git a/zookeeper.py b/zookeeper.py
index 0150462..a1966dc 100644
--- a/zookeeper.py
+++ b/zookeeper.py
@@ -72,7 +72,7 @@ class RenewableReleasableLease(NonBlockingLease):
         self.identifier = identifier
         self.utcnow = utcnow
 
-    def release(self):
+    def release(self) -> bool:
         """Release the lease, if it's presently being held."""
         self.client.ensure_path(self.path)
         holder_path = self.path + "/lease_holder"
@@ -81,7 +81,7 @@ class RenewableReleasableLease(NonBlockingLease):
             with lock:
                 if not self._is_lease_held_pre_locked():
                     logger.debug("Can't release lease; I don't have it!")
-                    return
+                    return False
 
                 now = self.utcnow()
                 if self.client.exists(holder_path):
@@ -92,9 +92,12 @@ class RenewableReleasableLease(NonBlockingLease):
                 data = {'version': self._version, 'holder': self.identifier, 'end': end_lease}
                 self.client.create(holder_path, self._encode(data))
                 self.obtained = False
+                logger.debug('Successfully released lease')
+                return True
 
-        except CancelledError:
-            pass
+        except CancelledError as e:
+            logger.debug('Exception %s in zookeeper?', e)
+        return False
 
     def try_renew(self, duration: datetime.timedelta) -> bool:
         if not self.obtained:
@@ -113,9 +116,8 @@ class RenewableReleasableLease(NonBlockingLease):
             if data["version"] != self._version:
                 return False
             current_end = datetime.datetime.strptime(data['end'], self._date_format)
-            if data['holder'] != self.identifier or now > current_end:
-                return False
-            else:
+            if data['holder'] == self.identifier and now <= current_end:
+                logger.debug('Yes, we hold the lease and it isn\'t expired.')
                 return True
         return False
 
@@ -208,10 +210,15 @@ def obtain_lease(
                 if also_pass_lease:
                     args = (*args, lease)
                 ret = func(*args, *kwargs)
+
+                # We don't care if this release operation succeeds;
+                # there are legitimate cases where it will fail such
+                # as when the user code has already voluntarily
+                # released the lease.
                 lease.release()
             else:
                 logger.debug(
-                    'Failed to obtain %s for contender %s, doing nothing more.',
+                    'Failed to obtain %s for contender %s, shutting down.',
                     lease_id,
                     contender_id,
                 )
@@ -318,15 +325,19 @@ def run_for_election(
                 args = (*args, self.zk)
             args = (*args, self.stop_event)
 
-            logger.debug('Invoking user code on separate thread.')
             thread = threading.Thread(
                 target=self.func,
                 args=args,
                 kwargs=kwargs,
             )
+            logger.debug(
+                'Invoking user code on separate thread: %s',
+                thread.getName(),
+            )
             thread.start()
 
-            # Watch the state (fail safe for listener) and the thread.
+            # Periodically poll the zookeeper state (fail safe for
+            # listener) and the state of the child thread.
             while True:
                 state = self.zk.client_state
                 if state != KazooState.CONNECTED:
@@ -337,11 +348,12 @@ def run_for_election(
                     self.stop_event.set()
                     logger.debug('Waiting for user thread to tear down...')
                     thread.join()
+                    logger.debug('User thread exited after our notification.')
                     return
 
                 thread.join(timeout=5.0)
                 if not thread.is_alive():
-                    logger.info('Child thread exited, I\'m exiting too.')
+                    logger.info('User thread exited on its own.')
                     return
 
         def __call__(self, *args, **kwargs):
-- 
2.46.0