Change ThreadLock to ThreadRLock to resolve rare deadlock

Author: Zenulous

httpcore/_sync/connection_pool.py

@@ -9,7 +9,7 @@
 from .._backends.base import SOCKET_OPTION, NetworkBackend
 from .._exceptions import ConnectionNotAvailable, UnsupportedProtocol
 from .._models import Origin, Proxy, Request, Response
-from .._synchronization import Event, ShieldCancellation, ThreadLock
+from .._synchronization import Event, ShieldCancellation, ThreadRLock
 from .connection import HTTPConnection
 from .interfaces import ConnectionInterface, RequestInterface
 
@@ -123,7 +123,7 @@ def __init__(
         # We only mutate the state of the connection pool within an 'optional_thread_lock'
         # context. This holds a threading lock unless we're running in async mode,
         # in which case it is a no-op.
-        self._optional_thread_lock = ThreadLock()
+        self._optional_thread_lock = ThreadRLock()
 
     def create_connection(self, origin: Origin) -> ConnectionInterface:
         if self._proxy is not None:

httpcore/_synchronization.py

@@ -94,7 +94,7 @@ class AsyncThreadLock:
     """
     This is a threading-only lock for no-I/O contexts.
 
-    In the sync case `ThreadLock` provides thread locking.
+    In the sync case `ThreadRLock` provides thread locking.
     In the async case `AsyncThreadLock` is a no-op.
     """
 
@@ -253,18 +253,19 @@ def __exit__(
         self._lock.release()
 
 
-class ThreadLock:
+class ThreadRLock:
     """
     This is a threading-only lock for no-I/O contexts.
+    The lock type is a reentrant lock.
 
-    In the sync case `ThreadLock` provides thread locking.
+    In the sync case `ThreadRLock` provides thread locking.
     In the async case `AsyncThreadLock` is a no-op.
     """
 
     def __init__(self) -> None:
-        self._lock = threading.Lock()
+        self._lock = threading.RLock()
 
-    def __enter__(self) -> ThreadLock:
+    def __enter__(self) -> ThreadRLock:
         self._lock.acquire()
         return self