Set maxsize of request queue to Quantum Engine (quantumlib#6576)

* set maxsize for request queue

* add max message size

cirq-google/cirq_google/cloud/quantum_v1alpha1/services/quantum_engine_service/transports/grpc.py

@@ -169,8 +169,9 @@ def __init__(
                 ssl_credentials=self._ssl_channel_credentials,
                 quota_project_id=quota_project_id,
                 options=[
-                    ("grpc.max_send_message_length", -1),
-                    ("grpc.max_receive_message_length", -1),
+                    ('grpc.max_send_message_length', 20 * 1024 * 1024),  # 20MiB
+                    ('grpc.max_receive_message_length', -1),  # unlimited
+                    ('grpc.max_metadata_length', 10 * 1024 * 1024),  # 10MiB
                 ],
             )
 

cirq-google/cirq_google/cloud/quantum_v1alpha1/services/quantum_engine_service/transports/grpc_asyncio.py

@@ -214,8 +214,9 @@ def __init__(
                 ssl_credentials=self._ssl_channel_credentials,
                 quota_project_id=quota_project_id,
                 options=[
-                    ("grpc.max_send_message_length", -1),
-                    ("grpc.max_receive_message_length", -1),
+                    ('grpc.max_send_message_length', 20 * 1024 * 1024),  # 20MiB
+                    ('grpc.max_receive_message_length', -1),  # unlimited
+                    ('grpc.max_metadata_length', 10 * 1024 * 1024),  # 10MiB
                 ],
             )
 

cirq-google/cirq_google/engine/stream_manager.py

@@ -123,7 +123,7 @@ async def _make_request_queue(self) -> asyncio.Queue[Optional[quantum.QuantumRun
 
         If `None` is put into the queue, the request iterator will stop.
         """
-        return asyncio.Queue()
+        return asyncio.Queue(maxsize=100)
 
     def submit(
         self, project_name: str, program: quantum.QuantumProgram, job: quantum.QuantumJob