fix(mcp): prevent MCPClient from hanging on exit#1847
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giulio-leone wants to merge 1 commit intostrands-agents:mainfrom
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fix(mcp): prevent MCPClient from hanging on exit#1847giulio-leone wants to merge 1 commit intostrands-agents:mainfrom
giulio-leone wants to merge 1 commit intostrands-agents:mainfrom
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…ad is unresponsive MCPClient.stop() called _background_thread.join() without a timeout, causing the process to hang indefinitely when the background thread could not be signaled (e.g., event loop already closed during interpreter shutdown or finalizer invocation). Changes: - Add cleanup_timeout parameter (default 5.0s) to MCPClient.__init__ - Use timeout in _background_thread.join() to prevent indefinite hangs - Catch RuntimeError from run_coroutine_threadsafe when the event loop is already closed - Log a warning when the thread does not stop within the timeout Fixes strands-agents#1732 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Bug
MCPClient.stop()hangs indefinitely when the background thread cannot be stopped, causing scripts to freeze on exit.Reported in: #1732
Root cause
_background_thread.join()was called without a timeout. Whenstop()is triggered fromAgent.__del__()(garbage collector) or during interpreter shutdown, the event loop may already be closed, sorun_coroutine_threadsafe(_set_close_event(), loop)silently fails (raisesRuntimeError). The background thread never receives the shutdown signal, andjoin()blocks forever.Fix
cleanup_timeoutparameter (default 5.0 seconds) toMCPClient.__init__()join(timeout=cleanup_timeout)instead of indefinitejoin()RuntimeErrorfromrun_coroutine_threadsafewhen the event loop is already closedTesting
test_stop_does_not_hang_when_background_thread_unresponsive— verifies timeout prevents hangtest_stop_handles_closed_event_loop— verifies graceful handling of closed event loopjoin()assertions to verify timeout parameterFixes #1732