Cache sync Functions clients

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 76f2163a-0773-4889-b627-1bd4e5c7bea0

Author: andystaples

azure-functions-durable/azure/durable_functions/client.py

@@ -2,7 +2,9 @@
 # Licensed under the MIT License.
 
 import asyncio
+import atexit
 import json
+import threading
 
 from datetime import datetime, timedelta
 from typing import Any, Optional, Union
@@ -30,6 +32,10 @@
 from .internal.compat.purge_history_result import PurgeHistoryResult
 
 
+_sync_client_cache: dict[str, "SyncDurableFunctionsClient"] = {}
+_sync_client_cache_lock = threading.Lock()
+
+
 # Client class used for Durable Functions
 class DurableFunctionsClient(AsyncTaskHubGrpcClient):
     """A gRPC client passed to Durable Functions durable client bindings.
@@ -527,6 +533,21 @@ def __init__(self, client_as_string: str):
             channel_options=channel_options,
             data_converter=DEFAULT_FUNCTIONS_DATA_CONVERTER)
 
+    @classmethod
+    def get_cached(cls, client_as_string: str) -> "SyncDurableFunctionsClient":
+        """Get the process-wide client for a durable-client binding configuration.
+
+        Synchronous Functions bindings can be invoked frequently by history
+        export fan-out activities. Reusing the gRPC channel avoids creating and
+        tearing down a channel for every activity invocation.
+        """
+        with _sync_client_cache_lock:
+            cached = _sync_client_cache.get(client_as_string)
+            if cached is None:
+                cached = cls(client_as_string)
+                _sync_client_cache[client_as_string] = cached
+            return cached
+
     def _parse_client_configuration(self, client_as_string: str) -> None:
         client = json.loads(client_as_string)
         self.taskHubName = client.get("taskHubName") or ""
@@ -585,3 +606,15 @@ def _get_instance_status_url(
                 f"/runtime/webhooks/durabletask/instances/{encoded_instance_id}")
         base_url = self.baseUrl.rstrip("/") if self.baseUrl else ""
         return f"{base_url}/instances/{encoded_instance_id}"
+
+
+def _close_cached_sync_clients() -> None:
+    """Release process-wide synchronous durable-client channels on shutdown."""
+    with _sync_client_cache_lock:
+        clients = list(_sync_client_cache.values())
+        _sync_client_cache.clear()
+    for client in clients:
+        client.close()
+
+
+atexit.register(_close_cached_sync_clients)

azure-functions-durable/azure/durable_functions/decorators/durable_app.py

@@ -415,7 +415,7 @@ async def client_bound(*args: Any, **kwargs: Any) -> Any:
                 if not isinstance(raw_client, str):
                     raise TypeError(
                         f"durable client binding '{client_name}' did not provide its configuration")
-                client = (SyncDurableFunctionsClient(raw_client) if sync
+                client = (SyncDurableFunctionsClient.get_cached(raw_client) if sync
                           else DurableFunctionsClient(raw_client))
                 bound.arguments[client_name] = client
                 try:
@@ -424,8 +424,6 @@ async def client_bound(*args: Any, **kwargs: Any) -> Any:
                 finally:
                     if isinstance(client, DurableFunctionsClient):
                         client.schedule_close()
-                    else:
-                        client.close()
 
             client_bound.__annotations__[client_name] = str
             setattr(client_bound, "client_function", function)

tests/azure-functions-durable/test_decorator_compat.py

@@ -135,12 +135,16 @@ async def starter(client):
 
 async def test_durable_client_input_sync_injects_sync_client():
     app = df.DFApp()
+    clients = []
 
     def starter(client):
+        clients.append(client)
         return type(client).__name__
 
     fb = app.durable_client_input_sync(client_name="client")(starter)
     assert await fb._function._func(client="{}") == "SyncDurableFunctionsClient"
+    assert await fb._function._func(client="{}") == "SyncDurableFunctionsClient"
+    assert clients[0] is clients[1]
 
 
 # ---------------------------------------------------------------------------