[Agent Engines] `_wrap_async_stream_query_operation` blocks asyncio event loop due to synchronous gRPC iteration

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#7,136 opened on Sep 8, 2026 2 comments 0 reactions 1 assignee View on GitHub

@maxgasztych is already working on this.

Since Sep 18, 2026.

Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 72/100

Issue type: Bug
Clarity: Clearly specified
Activity status: Active
Tech stack: grpc, python
Domain: api, backend

Research direction

Start in vertexai/agent_engines/_agent_engines.py at _wrap_async_stream_query_operation and compare the synchronous execution_api_client call with self.execution_async_client. Reproduce the stream with asyncio.run(..., debug=True); done means async_stream_query no longer blocks the event-loop thread during socket reads while still yielding parsed chunks.

Written by the indexing model from the issue text.

Description

api: vertex-ai

agent_engine.async_stream_query(...) blocks the calling asyncio event loop thread during stream generation.

In vertexai/agent_engines/_agent_engines.py, _wrap_async_stream_query_operation wraps a synchronous client call in an async def and uses a blocking for loop:

# CURRENT IMPLEMENTATION (vertexai/agent_engines/_agent_engines.py)
def _wrap_async_stream_query_operation(*, method_name: str):
    async def _method(self, **kwargs):
        # 1. Uses sync client instead of self.execution_async_client
        response = self.execution_api_client.stream_query_reasoning_engine(...)
        # 2. Synchronous iteration blocks the asyncio event loop on socket reads
        for chunk in response:
            for parsed_json in _utils.yield_parsed_json(chunk):
                if parsed_json is not None:
                    yield parsed_json
    return _method

Reproduction:

import asyncio
from vertexai import agent_engines

agent = agent_engines.get("projects/<P>/locations/<L>/reasoningEngines/<ID>")

async def main():
    async for chunk in agent.async_stream_query(user_id="u", message="Long prompt"):
        pass

asyncio.run(main(), debug=True)
# Result: Emits "Executing <Task ...> took X.XX seconds" because the thread is blocked on socket reads without yielding.

Dominant language: Python
Stars: 907
Forks: 467
Avg merge: 1d 13h
Merged PRs (30d): 44

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