Merge pull request #599 from pmazzini/lock

feat(core): interoperate with Go client

4 files changed, 209 insertions, 109 deletions

diff --git a/.flake8 b/.flake8
new file mode 100644
index 0000000..20d6db4
--- /dev/null
+++ b/.flake8
@@ -0,0 +1,2 @@
+[flake8]
+ignore = BLK100
diff --git a/.hound.yml b/.hound.yml
index 5de48c8..5f00754 100644
--- a/.hound.yml
+++ b/.hound.yml
@@ -1,3 +1,4 @@
 fail_on_violations: true
 python:
   enabled: true
+  config_file: .flake8
diff --git a/kazoo/recipe/lock.py b/kazoo/recipe/lock.py
index 9bd5dc0..7722a97 100644
--- a/kazoo/recipe/lock.py
+++ b/kazoo/recipe/lock.py
@@ -14,7 +14,9 @@ changes and re-act appropriately. In the event that a
 and/or the lease has been lost.
 
 """
+import re
 import sys
+
 try:
     from time import monotonic as now
 except ImportError:
@@ -27,13 +29,13 @@ from kazoo.exceptions import (
     CancelledError,
     KazooException,
     LockTimeout,
-    NoNodeError
+    NoNodeError,
 )
 from kazoo.protocol.states import KazooState
 from kazoo.retry import (
     ForceRetryError,
     KazooRetry,
-    RetryFailedError
+    RetryFailedError,
 )
 
 
@@ -82,22 +84,38 @@ class Lock(object):
     # sequence number. Involved in read/write locks.
     _EXCLUDE_NAMES = ["__lock__"]
 
-    def __init__(self, client, path, identifier=None):
+    def __init__(self, client, path, identifier=None, extra_lock_patterns=()):
         """Create a Kazoo lock.
 
         :param client: A :class:`~kazoo.client.KazooClient` instance.
         :param path: The lock path to use.
-        :param identifier: Name to use for this lock contender. This
-                           can be useful for querying to see who the
-                           current lock contenders are.
-
+        :param identifier: Name to use for this lock contender. This can be
+                          useful for querying to see who the current lock
+                          contenders are.
+        :param extra_lock_patterns: Strings that will be used to
+                                    identify other znode in the path
+                                    that should be considered contenders
+                                    for this lock.
+                                    Use this for cross-implementation
+                                    compatibility.
+
+        .. versionadded:: 2.7.1
+            The extra_lock_patterns option.
         """
         self.client = client
         self.path = path
+        self._exclude_names = set(
+            self._EXCLUDE_NAMES + list(extra_lock_patterns)
+        )
+        self._contenders_re = re.compile(
+            r"(?:{patterns})(-?\d{{10}})$".format(
+                patterns="|".join(self._exclude_names)
+            )
+        )
 
         # some data is written to the node. this can be queried via
         # contenders() to see who is contending for the lock
-        self.data = str(identifier or "").encode('utf-8')
+        self.data = str(identifier or "").encode("utf-8")
         self.node = None
 
         self.wake_event = client.handler.event_object()
@@ -113,8 +131,9 @@ class Lock(object):
         self.is_acquired = False
         self.assured_path = False
         self.cancelled = False
-        self._retry = KazooRetry(max_tries=None,
-                                 sleep_func=client.handler.sleep_func)
+        self._retry = KazooRetry(
+            max_tries=None, sleep_func=client.handler.sleep_func
+        )
         self._lock = client.handler.lock_object()
 
     def _ensure_path(self):
@@ -171,6 +190,7 @@ class Lock(object):
             return False
         if not locked:
             # Lock acquire doesn't take a timeout, so simulate it...
+            # XXX: This is not true in Py3 >= 3.2
             try:
                 locked = retry(_acquire_lock)
             except RetryFailedError:
@@ -179,9 +199,12 @@ class Lock(object):
         try:
             gotten = False
             try:
-                gotten = retry(self._inner_acquire,
-                               blocking=blocking, timeout=timeout,
-                               ephemeral=ephemeral)
+                gotten = retry(
+                    self._inner_acquire,
+                    blocking=blocking,
+                    timeout=timeout,
+                    ephemeral=ephemeral,
+                )
             except RetryFailedError:
                 pass
             except KazooException:
@@ -222,8 +245,9 @@ class Lock(object):
             self.create_tried = True
 
         if not node:
-            node = self.client.create(self.create_path, self.data,
-                                      ephemeral=ephemeral, sequence=True)
+            node = self.client.create(
+                self.create_path, self.data, ephemeral=ephemeral, sequence=True
+            )
             # strip off path to node
             node = node[len(self.path) + 1:]
 
@@ -236,18 +260,8 @@ class Lock(object):
             if self.cancelled:
                 raise CancelledError()
 
-            children = self._get_sorted_children()
-
-            try:
-                our_index = children.index(node)
-            except ValueError:  # pragma: nocover
-                # somehow we aren't in the children -- probably we are
-                # recovering from a session failure and our ephemeral
-                # node was removed
-                raise ForceRetryError()
-
-            predecessor = self.predecessor(children, our_index)
-            if not predecessor:
+            predecessor = self._get_predecessor(node)
+            if predecessor is None:
                 return True
 
             if not blocking:
@@ -263,40 +277,51 @@ class Lock(object):
             else:
                 self.wake_event.wait(timeout)
                 if not self.wake_event.isSet():
-                    raise LockTimeout("Failed to acquire lock on %s after "
-                                      "%s seconds" % (self.path, timeout))
+                    raise LockTimeout(
+                        "Failed to acquire lock on %s after %s seconds"
+                        % (self.path, timeout)
+                    )
             finally:
                 self.client.remove_listener(self._watch_session)
 
-    def predecessor(self, children, index):
-        for c in reversed(children[:index]):
-            if any(n in c for n in self._EXCLUDE_NAMES):
-                return c
-        return None
-
     def _watch_predecessor(self, event):
         self.wake_event.set()
 
-    def _get_sorted_children(self):
+    def _get_predecessor(self, node):
+        """returns `node`'s predecessor or None
+
+        Note: This handle the case where the current lock is not a contender
+        (e.g. rlock), this and also edge cases where the lock's ephemeral node
+        is gone.
+        """
         children = self.client.get_children(self.path)
+        found_self = False
+        # Filter out the contenders using the computed regex
+        contender_matches = []
+        for child in children:
+            match = self._contenders_re.search(child)
+            if match is not None:
+                contender_matches.append(match)
+            if child == node:
+                # Remember the node's match object so we can short circuit
+                # below.
+                found_self = match
+
+        if found_self is False:  # pragma: nocover
+            # somehow we aren't in the childrens -- probably we are
+            # recovering from a session failure and our ephemeral
+            # node was removed.
+            raise ForceRetryError()
+
+        predecessor = None
+        # Sort the contenders using the sequence number extracted by the regex,
+        # then extract the original string.
+        for match in sorted(contender_matches, key=lambda m: m.groups()):
+            if match is found_self:
+                break
+            predecessor = match.string
 
-        # Node names are prefixed by a type: strip the prefix first, which may
-        # be one of multiple values in case of a read-write lock, and return
-        # only the sequence number (as a string since it is padded and will
-        # sort correctly anyway).
-        #
-        # In some cases, the lock path may contain nodes with other prefixes
-        # (eg. in case of a lease), just sort them last ('~' sorts after all
-        # ASCII digits).
-        def _seq(c):
-            for name in ["__lock__", "__rlock__"]:
-                idx = c.find(name)
-                if idx != -1:
-                    return c[idx + len(name):]
-            # Sort unknown node names eg. "lease_holder" last.
-            return '~'
-        children.sort(key=_seq)
-        return children
+        return predecessor
 
     def _find_node(self):
         children = self.client.get_children(self.path)
@@ -347,16 +372,37 @@ class Lock(object):
         if not self.assured_path:
             self._ensure_path()
 
-        children = self._get_sorted_children()
-
-        contenders = []
+        children = self.client.get_children(self.path)
+        # We want all contenders, including self (this is especially important
+        # for r/w locks). This is similar to the logic of `_get_predecessor`
+        # except we include our own pattern.
+        all_contenders_re = re.compile(
+            r"(?:{patterns})(-?\d{{10}})$".format(
+                patterns="|".join(self._exclude_names | {self._NODE_NAME})
+            )
+        )
+        # Filter out the contenders using the computed regex
+        contender_matches = []
         for child in children:
+            match = all_contenders_re.search(child)
+            if match is not None:
+                contender_matches.append(match)
+        # Sort the contenders using the sequence number extracted by the regex,
+        # then extract the original string.
+        contender_nodes = [
+            match.string
+            for match in sorted(contender_matches, key=lambda m: m.groups())
+        ]
+        # Retrieve all the contender nodes data (preserving order).
+        contenders = []
+        for node in contender_nodes:
             try:
-                data, stat = self.client.get(self.path + "/" + child)
+                data, stat = self.client.get(self.path + "/" + node)
                 if data is not None:
-                    contenders.append(data.decode('utf-8'))
+                    contenders.append(data.decode("utf-8"))
             except NoNodeError:  # pragma: nocover
                 pass
+
         return contenders
 
     def __enter__(self):
@@ -391,6 +437,7 @@ class WriteLock(Lock):
     shared lock.
 
     """
+
     _NODE_NAME = "__lock__"
     _EXCLUDE_NAMES = ["__lock__", "__rlock__"]
 
@@ -420,6 +467,7 @@ class ReadLock(Lock):
     shared lock.
 
     """
+
     _NODE_NAME = "__rlock__"
     _EXCLUDE_NAMES = ["__lock__"]
 
@@ -458,6 +506,7 @@ class Semaphore(object):
         The max_leases check.
 
     """
+
     def __init__(self, client, path, identifier=None, max_leases=1):
         """Create a Kazoo Lock
 
@@ -483,12 +532,12 @@ class Semaphore(object):
 
         # some data is written to the node. this can be queried via
         # contenders() to see who is contending for the lock
-        self.data = str(identifier or "").encode('utf-8')
+        self.data = str(identifier or "").encode("utf-8")
         self.max_leases = max_leases
         self.wake_event = client.handler.event_object()
 
         self.create_path = self.path + "/" + uuid.uuid4().hex
-        self.lock_path = path + '-' + '__lock__'
+        self.lock_path = path + "-" + "__lock__"
         self.is_acquired = False
         self.assured_path = False
         self.cancelled = False
@@ -501,7 +550,7 @@ class Semaphore(object):
             # node did already exist
             data, _ = self.client.get(self.path)
             try:
-                leases = int(data.decode('utf-8'))
+                leases = int(data.decode("utf-8"))
             except (ValueError, TypeError):
                 # ignore non-numeric data, maybe the node data is used
                 # for other purposes
@@ -509,11 +558,11 @@ class Semaphore(object):
             else:
                 if leases != self.max_leases:
                     raise ValueError(
-                        "Inconsistent max leases: %s, expected: %s" %
-                        (leases, self.max_leases)
+                        "Inconsistent max leases: %s, expected: %s"
+                        % (leases, self.max_leases)
                     )
         else:
-            self.client.set(self.path, str(self.max_leases).encode('utf-8'))
+            self.client.set(self.path, str(self.max_leases).encode("utf-8"))
 
     def cancel(self):
         """Cancel a pending semaphore acquire."""
@@ -548,7 +597,8 @@ class Semaphore(object):
 
         try:
             self.is_acquired = self.client.retry(
-                self._inner_acquire, blocking=blocking, timeout=timeout)
+                self._inner_acquire, blocking=blocking, timeout=timeout
+            )
         except KazooException:
             # if we did ultimately fail, attempt to clean up
             self._best_effort_cleanup()
@@ -590,8 +640,9 @@ class Semaphore(object):
                     self.wake_event.wait(w.leftover())
                     if not self.wake_event.isSet():
                         raise LockTimeout(
-                            "Failed to acquire semaphore on %s "
-                            "after %s seconds" % (self.path, timeout))
+                            "Failed to acquire semaphore on %s"
+                            " after %s seconds" % (self.path, timeout)
+                        )
                 else:
                     return False
         finally:
@@ -612,8 +663,9 @@ class Semaphore(object):
         # Get a list of the current potential lock holders. If they change,
         # notify our wake_event object. This is used to unblock a blocking
         # self._inner_acquire call.
-        children = self.client.get_children(self.path,
-                                            self._watch_lease_change)
+        children = self.client.get_children(
+            self.path, self._watch_lease_change
+        )
 
         # If there are leases available, acquire one
         if len(children) < self.max_leases:
@@ -674,7 +726,7 @@ class Semaphore(object):
         for child in children:
             try:
                 data, stat = self.client.get(self.path + "/" + child)
-                lease_holders.append(data.decode('utf-8'))
+                lease_holders.append(data.decode("utf-8"))
             except NoNodeError:  # pragma: nocover
                 pass
         return lease_holders
diff --git a/kazoo/tests/test_lock.py b/kazoo/tests/test_lock.py
index ee0ff3d..0e16949 100644
--- a/kazoo/tests/test_lock.py
+++ b/kazoo/tests/test_lock.py
@@ -1,5 +1,7 @@
 import collections
+import mock
 import threading
+import unittest
 import uuid
 
 import pytest
@@ -7,6 +9,7 @@ import pytest
 from kazoo.exceptions import CancelledError
 from kazoo.exceptions import LockTimeout
 from kazoo.exceptions import NoNodeError
+from kazoo.recipe.lock import Lock
 from kazoo.testing import KazooTestCase
 from kazoo.tests import util as test_util
 
@@ -97,8 +100,10 @@ class KazooLockTests(KazooTestCase):
         lock_name = uuid.uuid4().hex
         lock = self.client.Lock(self.lockpath, lock_name)
         event = self.make_event()
-        thread = self.make_thread(target=self._thread_lock_acquire_til_event,
-                                  args=(lock_name, lock, event))
+        thread = self.make_thread(
+            target=self._thread_lock_acquire_til_event,
+            args=(lock_name, lock, event),
+        )
         thread.start()
 
         lock2_name = uuid.uuid4().hex
@@ -131,8 +136,9 @@ class KazooLockTests(KazooTestCase):
         for name in names:
             e = self.make_event()
             l = self.client.Lock(self.lockpath, name)
-            t = self.make_thread(target=self._thread_lock_acquire_til_event,
-                                 args=(name, l, e))
+            t = self.make_thread(
+                target=self._thread_lock_acquire_til_event, args=(name, l, e)
+            )
             contender_bits[name] = (t, e)
             threads.append(t)
 
@@ -176,9 +182,11 @@ class KazooLockTests(KazooTestCase):
 
     def test_lock_reconnect(self):
         event = self.make_event()
-        other_lock = self.client.Lock(self.lockpath, 'contender')
-        thread = self.make_thread(target=self._thread_lock_acquire_til_event,
-                                  args=('contender', other_lock, event))
+        other_lock = self.client.Lock(self.lockpath, "contender")
+        thread = self.make_thread(
+            target=self._thread_lock_acquire_til_event,
+            args=("contender", other_lock, event),
+        )
 
         # acquire the lock ourselves first to make the contender line up
         lock = self.client.Lock(self.lockpath, "test")
@@ -188,7 +196,7 @@ class KazooLockTests(KazooTestCase):
         # wait for the contender to line up on the lock
         wait = self.make_wait()
         wait(lambda: len(lock.contenders()) == 2)
-        assert lock.contenders() == ['test', 'contender']
+        assert lock.contenders() == ["test", "contender"]
 
         self.expire_session(self.make_event)
 
@@ -197,7 +205,7 @@ class KazooLockTests(KazooTestCase):
         with self.condition:
             while not self.active_thread:
                 self.condition.wait()
-            assert self.active_thread == 'contender'
+            assert self.active_thread == "contender"
 
         event.set()
         thread.join()
@@ -207,8 +215,10 @@ class KazooLockTests(KazooTestCase):
         lock = self.client.Lock(self.lockpath, lock_name)
         event = self.make_event()
 
-        thread = self.make_thread(target=self._thread_lock_acquire_til_event,
-                                  args=(lock_name, lock, event))
+        thread = self.make_thread(
+            target=self._thread_lock_acquire_til_event,
+            args=(lock_name, lock, event),
+        )
         thread.start()
 
         lock1 = self.client.Lock(self.lockpath, lock_name)
@@ -227,8 +237,10 @@ class KazooLockTests(KazooTestCase):
     def test_lock_fail_first_call(self):
         event1 = self.make_event()
         lock1 = self.client.Lock(self.lockpath, "one")
-        thread1 = self.make_thread(target=self._thread_lock_acquire_til_event,
-                                   args=("one", lock1, event1))
+        thread1 = self.make_thread(
+            target=self._thread_lock_acquire_til_event,
+            args=("one", lock1, event1),
+        )
         thread1.start()
 
         # wait for this thread to acquire the lock
@@ -243,8 +255,10 @@ class KazooLockTests(KazooTestCase):
     def test_lock_cancel(self):
         event1 = self.make_event()
         lock1 = self.client.Lock(self.lockpath, "one")
-        thread1 = self.make_thread(target=self._thread_lock_acquire_til_event,
-                                   args=("one", lock1, event1))
+        thread1 = self.make_thread(
+            target=self._thread_lock_acquire_til_event,
+            args=("one", lock1, event1),
+        )
         thread1.start()
 
         # wait for this thread to acquire the lock
@@ -257,8 +271,10 @@ class KazooLockTests(KazooTestCase):
         client2.start()
         event2 = self.make_event()
         lock2 = client2.Lock(self.lockpath, "two")
-        thread2 = self.make_thread(target=self._thread_lock_acquire_til_event,
-                                   args=("two", lock2, event2))
+        thread2 = self.make_thread(
+            target=self._thread_lock_acquire_til_event,
+            args=("two", lock2, event2),
+        )
         thread2.start()
 
         # this one should block in acquire. check that it is a contender
@@ -361,7 +377,7 @@ class KazooLockTests(KazooTestCase):
         client1.start()
         lock = client1.Lock(self.lockpath, "ephemeral")
         lock.acquire(ephemeral=False)
-        znode = self.lockpath + '/' + lock.node
+        znode = self.lockpath + "/" + lock.node
         client1.stop()
         try:
             self.client.get(znode)
@@ -418,7 +434,6 @@ class KazooLockTests(KazooTestCase):
         # and that it's still not reentrant.
         gotten = lock.acquire(blocking=False)
         assert gotten is False
-
         # Test that a second client we can share the same read lock
         client2 = self._get_client()
         client2.start()
@@ -428,7 +443,6 @@ class KazooLockTests(KazooTestCase):
         assert lock2.is_acquired is True
         gotten = lock2.acquire(blocking=False)
         assert gotten is False
-
         # Test that a writer is unable to share it
         client3 = self._get_client()
         client3.start()
@@ -518,28 +532,33 @@ class TestSemaphore(KazooTestCase):
 
     def test_non_blocking(self):
         sem1 = self.client.Semaphore(
-            self.lockpath, identifier='sem1', max_leases=2)
+            self.lockpath, identifier="sem1", max_leases=2
+        )
         sem2 = self.client.Semaphore(
-            self.lockpath, identifier='sem2', max_leases=2)
+            self.lockpath, identifier="sem2", max_leases=2
+        )
         sem3 = self.client.Semaphore(
-            self.lockpath, identifier='sem3', max_leases=2)
+            self.lockpath, identifier="sem3", max_leases=2
+        )
 
         sem1.acquire()
         sem2.acquire()
         assert not sem3.acquire(blocking=False)
-        assert set(sem1.lease_holders()) == set(['sem1', 'sem2'])
+        assert set(sem1.lease_holders()) == set(["sem1", "sem2"])
         sem2.release()
         # the next line isn't required, but avoids timing issues in tests
         sem3.acquire()
-        assert set(sem1.lease_holders()) == set(['sem1', 'sem3'])
+        assert set(sem1.lease_holders()) == set(["sem1", "sem3"])
         sem1.release()
         sem3.release()
 
     def test_non_blocking_release(self):
         sem1 = self.client.Semaphore(
-            self.lockpath, identifier='sem1', max_leases=1)
+            self.lockpath, identifier="sem1", max_leases=1
+        )
         sem2 = self.client.Semaphore(
-            self.lockpath, identifier='sem2', max_leases=1)
+            self.lockpath, identifier="sem2", max_leases=1
+        )
         sem1.acquire()
         sem2.acquire(blocking=False)
 
@@ -552,7 +571,7 @@ class TestSemaphore(KazooTestCase):
         event = self.make_event()
 
         def sema_one():
-            with self.client.Semaphore(self.lockpath, 'fred', max_leases=1):
+            with self.client.Semaphore(self.lockpath, "fred", max_leases=1):
                 started.set()
                 event.wait()
 
@@ -561,13 +580,13 @@ class TestSemaphore(KazooTestCase):
         started.wait()
         sem1 = self.client.Semaphore(self.lockpath)
         holders = sem1.lease_holders()
-        assert holders == ['fred']
+        assert holders == ["fred"]
         event.set()
         thread.join()
 
     def test_semaphore_cancel(self):
-        sem1 = self.client.Semaphore(self.lockpath, 'fred', max_leases=1)
-        sem2 = self.client.Semaphore(self.lockpath, 'george', max_leases=1)
+        sem1 = self.client.Semaphore(self.lockpath, "fred", max_leases=1)
+        sem2 = self.client.Semaphore(self.lockpath, "george", max_leases=1)
         sem1.acquire()
         started = self.make_event()
         event = self.make_event()
@@ -583,7 +602,7 @@ class TestSemaphore(KazooTestCase):
         thread = self.make_thread(target=sema_one, args=())
         thread.start()
         started.wait()
-        assert sem1.lease_holders() == ['fred']
+        assert sem1.lease_holders() == ["fred"]
         assert not event.is_set()
         sem2.cancel()
         event.wait()
@@ -591,7 +610,7 @@ class TestSemaphore(KazooTestCase):
         thread.join()
 
     def test_multiple_acquire_and_release(self):
-        sem1 = self.client.Semaphore(self.lockpath, 'fred', max_leases=1)
+        sem1 = self.client.Semaphore(self.lockpath, "fred", max_leases=1)
         sem1.acquire()
         sem1.acquire()
 
@@ -599,12 +618,13 @@ class TestSemaphore(KazooTestCase):
         assert not sem1.release()
 
     def test_handle_session_loss(self):
-        expire_semaphore = self.client.Semaphore(self.lockpath, 'fred',
-                                                 max_leases=1)
+        expire_semaphore = self.client.Semaphore(
+            self.lockpath, "fred", max_leases=1
+        )
 
         client = self._get_client()
         client.start()
-        lh_semaphore = client.Semaphore(self.lockpath, 'george', max_leases=1)
+        lh_semaphore = client.Semaphore(self.lockpath, "george", max_leases=1)
         lh_semaphore.acquire()
 
         started = self.make_event()
@@ -621,7 +641,7 @@ class TestSemaphore(KazooTestCase):
         thread1.start()
 
         started.wait()
-        assert lh_semaphore.lease_holders() == ['george']
+        assert lh_semaphore.lease_holders() == ["george"]
 
         # Fired in a separate thread to make sure we can see the effect
         expired = self.make_event()
@@ -639,7 +659,7 @@ class TestSemaphore(KazooTestCase):
         client.stop()
 
         event.wait(15)
-        assert expire_semaphore.lease_holders() == ['fred']
+        assert expire_semaphore.lease_holders() == ["fred"]
         event2.set()
 
         for t in (thread1, thread2):
@@ -658,7 +678,7 @@ class TestSemaphore(KazooTestCase):
         sem2 = self.client.Semaphore(self.lockpath, max_leases=2)
 
         self.client.ensure_path(self.lockpath)
-        self.client.set(self.lockpath, b'a$')
+        self.client.set(self.lockpath, b"a$")
 
         sem1.acquire()
         # sem2 thinks it's ok to have two lease holders
@@ -716,3 +736,28 @@ class TestSemaphore(KazooTestCase):
             # Cleanup
             t.join()
             client2.stop()
+
+
+class TestSequence(unittest.TestCase):
+    def test_get_predecessor(self):
+        """Validate selection of predecessors.
+        """
+        goLock = "_c_8eb60557ba51e0da67eefc47467d3f34-lock-0000000031"
+        pyLock = "514e5a831836450cb1a56c741e990fd8__lock__0000000032"
+        children = ["hello", goLock, "world", pyLock]
+        client = mock.MagicMock()
+        client.get_children.return_value = children
+        lock = Lock(client, "test")
+        assert lock._get_predecessor(pyLock) is None
+
+    def test_get_predecessor_go(self):
+        """Test selection of predecessor when instructed to consider go-zk
+        locks.
+        """
+        goLock = "_c_8eb60557ba51e0da67eefc47467d3f34-lock-0000000031"
+        pyLock = "514e5a831836450cb1a56c741e990fd8__lock__0000000032"
+        children = ["hello", goLock, "world", pyLock]
+        client = mock.MagicMock()
+        client.get_children.return_value = children
+        lock = Lock(client, "test", extra_lock_patterns=["-lock-"])
+        assert lock._get_predecessor(pyLock) == goLock