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Fix dead locks in connection pool #499

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Merged
merged 4 commits into from
Jul 11, 2025
Merged

Fix dead locks in connection pool #499

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2f0ec39
fix: make HostConnection.return_connection not to lock connection and
dkropachev Jul 8, 2025
63b1148
fix: HostConnectionPool.return_connection not to lock connection and
dkropachev Jul 8, 2025
1687d4b
fix: HostConnectionPool._maybe_trash_connection not to lock connection
dkropachev Jul 8, 2025
729f9cc
fix: HostConnection._open_connection_to_missing_shard not to lock pool
dkropachev Jul 8, 2025
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101 changes: 55 additions & 46 deletions cassandra/pool.py
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Original file line number Diff line number Diff line change
Expand Up @@ -580,16 +580,18 @@ def return_connection(self, connection, stream_was_orphaned=False):
return
self._is_replacing = True
self._session.submit(self._replace, connection)
else:
if connection in self._trash:
with connection.lock:
if connection.in_flight == len(connection.orphaned_request_ids):
with self._lock:
if connection in self._trash:
self._trash.remove(connection)
log.debug("Closing trashed connection (%s) to %s", id(connection), self.host)
connection.close()
return
elif connection in self._trash:
with connection.lock:
no_pending_requests = connection.in_flight <= len(connection.orphaned_request_ids)
if no_pending_requests:
with self._lock:
close_connection = False
if connection in self._trash:
self._trash.remove(connection)
close_connection = True
if close_connection:
log.debug("Closing trashed connection (%s) to %s", id(connection), self.host)
connection.close()

def on_orphaned_stream_released(self):
"""
Expand Down Expand Up @@ -756,23 +758,26 @@ def _open_connection_to_missing_shard(self, shard_id):
)
old_conn = None
with self._lock:
if self.is_shutdown:
conn.close()
return
if conn.features.shard_id in self._connections.keys():
# Move the current connection to the trash and use the new one from now on
old_conn = self._connections[conn.features.shard_id]
log.debug(
"Replacing overloaded connection (%s) with (%s) for shard %i for host %s",
id(old_conn),
id(conn),
conn.features.shard_id,
self.host
)
if self._keyspace:
conn.set_keyspace_blocking(self._keyspace)
is_shutdown = self.is_shutdown
if not is_shutdown:
if conn.features.shard_id in self._connections.keys():
# Move the current connection to the trash and use the new one from now on
old_conn = self._connections[conn.features.shard_id]
log.debug(
"Replacing overloaded connection (%s) with (%s) for shard %i for host %s",
id(old_conn),
id(conn),
conn.features.shard_id,
self.host
)
if self._keyspace:
conn.set_keyspace_blocking(self._keyspace)
self._connections[conn.features.shard_id] = conn

if is_shutdown:
conn.close()
return

self._connections[conn.features.shard_id] = conn
if old_conn is not None:
remaining = old_conn.in_flight - len(old_conn.orphaned_request_ids)
if remaining == 0:
Expand All @@ -792,10 +797,11 @@ def _open_connection_to_missing_shard(self, shard_id):
remaining,
)
with self._lock:
if self.is_shutdown:
old_conn.close()
else:
is_shutdown = self.is_shutdown
if not is_shutdown:
self._trash.add(old_conn)
if is_shutdown:
conn.close()
num_missing_or_needing_replacement = self.num_missing_or_needing_replacement
log.debug(
"Connected to %s/%i shards on host %s (%i missing or needs replacement)",
Expand Down Expand Up @@ -1132,15 +1138,18 @@ def return_connection(self, connection, stream_was_orphaned=False):
self.shutdown()
else:
self._replace(connection)
else:
if connection in self._trash:
with connection.lock:
if connection.in_flight == 0:
with self._lock:
if connection in self._trash:
self._trash.remove(connection)
log.debug("Closing trashed connection (%s) to %s", id(connection), self.host)
connection.close()
elif connection in self._trash:
with connection.lock:
no_pending_requests = connection.in_flight <= len(connection.orphaned_request_ids)
if no_pending_requests:
with self._lock:
close_connection = False
if connection in self._trash:
self._trash.remove(connection)
close_connection = True
if close_connection:
log.debug("Closing trashed connection (%s) to %s", id(connection), self.host)
connection.close()
return

core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance)
Expand Down Expand Up @@ -1175,14 +1184,14 @@ def _maybe_trash_connection(self, connection):
new_connections.remove(connection)
self._connections = new_connections

with connection.lock:
if connection.in_flight == 0:
log.debug("Skipping trash and closing unused connection (%s) to %s", id(connection), self.host)
connection.close()

# skip adding it to the trash if we're already closing it
return

if did_trash:
with connection.lock:
no_pending_requests = connection.in_flight <= len(connection.orphaned_request_ids)
if no_pending_requests:
log.debug("Skipping trash and closing unused connection (%s) to %s", id(connection), self.host)
connection.close()
return
with self._lock:
self._trash.add(connection)

if did_trash:
Expand Down
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