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https://github.com/PrefectHQ/fastmcp.git
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0adecf15df
Add GC call and yield after stdio_client context exits to clean up asyncio subprocess transport references while the loop is still running.
114 lines
3.7 KiB
Python
114 lines
3.7 KiB
Python
"""
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Test for issue #2792: Event loop is closed warning during subprocess transport cleanup.
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This test attempts to reproduce the warning that appears on Linux/CI when using
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StdioTransport with pytest. The issue is that asyncio's BaseSubprocessTransport.__del__
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tries to use the event loop after it's been closed by pytest-asyncio.
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The warning looks like:
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PytestUnraisableExceptionWarning: Exception ignored in:
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<function BaseSubprocessTransport.__del__ at ...>
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RuntimeError: Event loop is closed
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See: https://github.com/jlowin/fastmcp/issues/2792
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"""
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import asyncio
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import gc
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import inspect
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import pytest
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from fastmcp import Client
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from fastmcp.client.transports import PythonStdioTransport
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@pytest.fixture
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def simple_server_script(tmp_path):
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"""Create a minimal MCP server script."""
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script = inspect.cleandoc("""
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from fastmcp import FastMCP
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mcp = FastMCP()
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@mcp.tool
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def echo(message: str) -> str:
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return message
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if __name__ == "__main__":
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mcp.run()
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""")
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script_file = tmp_path / "simple_server.py"
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script_file.write_text(script)
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return script_file
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class TestStdioCleanup:
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"""Test suite for stdio transport cleanup issues."""
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@pytest.mark.timeout(30)
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@pytest.mark.filterwarnings("error::pytest.PytestUnraisableExceptionWarning")
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async def test_stdio_transport_cleanup_no_warning(self, simple_server_script):
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"""Test that stdio transport doesn't produce event loop warnings on cleanup.
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This test fails if a PytestUnraisableExceptionWarning is raised during
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cleanup, which happens when BaseSubprocessTransport.__del__ tries to
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use a closed event loop.
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"""
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transport = PythonStdioTransport(
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script_path=simple_server_script, keep_alive=False
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)
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client = Client(transport=transport)
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async with client:
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result = await client.call_tool("echo", {"message": "test"})
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assert result.data == "test"
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# The warning typically appears after the test completes and the event
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# loop is closed, then GC runs. We can try to force it by:
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# 1. Explicitly deleting references
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del client
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del transport
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# 2. Running GC while the loop is still open
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gc.collect()
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# 3. Yielding to let any pending callbacks run
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await asyncio.sleep(0.1)
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@pytest.mark.timeout(30)
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@pytest.mark.filterwarnings("error::pytest.PytestUnraisableExceptionWarning")
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async def test_stdio_transport_with_keep_alive_cleanup(self, simple_server_script):
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"""Test that keep_alive=True also cleans up properly when explicitly closed."""
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transport = PythonStdioTransport(
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script_path=simple_server_script, keep_alive=True
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)
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client = Client(transport=transport)
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async with client:
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result = await client.call_tool("echo", {"message": "test"})
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assert result.data == "test"
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# Explicitly close even though keep_alive=True
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await client.close()
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del client
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del transport
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gc.collect()
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await asyncio.sleep(0.1)
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@pytest.mark.timeout(30)
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@pytest.mark.filterwarnings("error::pytest.PytestUnraisableExceptionWarning")
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async def test_direct_disconnect_then_gc(self, simple_server_script):
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"""Test explicit disconnect followed by GC."""
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transport = PythonStdioTransport(
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script_path=simple_server_script, keep_alive=True
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)
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await transport.connect()
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await transport.disconnect()
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# Try to force any lingering references to be collected
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del transport
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gc.collect()
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await asyncio.sleep(0.1)
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