Add regression tests for #555, #559, #765 #1044
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**NOTE: These tests FAIL without the changes introduced in #559** - test_stdio_client_universal_timeout - test_stdio_client_immediate_completion await read_stream.aclose() await write_stream.aclose() await read_stream_writer.aclose() await write_stream_reader.aclose() These tests verify that stdio_client completes cleanup within reasonable time for both slow-terminating and fast-exiting processes, preventing the hanging issues reported in #559. **NOTE: This test FAILS without the changes introduced in #555** - test_stdio_client_sigint_only_process try: process.terminate() with anyio.fail_after(2.0): await process.wait() except TimeoutError: # If process doesn't terminate in time, force kill it process.kill() This test verifies that on UNIX systems MCP servers that don't respect SIGTERM but e.g. SIGINT still get terminated after a grace period.
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Following the MCP spec recommendations, the shutdown sequence now: 1. Closes stdin first to allow graceful server exit 2. Waits 2 seconds for the server to exit on its own 3. Only escalates to SIGTERM if the server doesn't exit 4. Finally uses SIGKILL as a last resort This unified approach works consistently across all platforms and gives well-behaved servers a chance to exit cleanly without signals. Co-Authored-By: davenpi <[email protected]>
Added two tests to validate the stdin-first shutdown behavior: 1. test_stdio_client_graceful_stdin_exit: Verifies that a well-behaved server exits cleanly when stdin is closed, without needing signals 2. test_stdio_client_stdin_close_ignored: Tests proper escalation to SIGTERM when a process ignores stdin closure These tests ensure the MCP spec shutdown sequence works correctly and provides graceful exit opportunities before using forceful termination.
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- Add process group support on POSIX systems via start_new_session=True - Implement _terminate_process_with_children() and _kill_process_and_children() functions that properly handle child process cleanup - On POSIX: Kill entire process group at once to avoid orphaning children when parent dies first - On Windows: Use taskkill /T for process tree termination - Add pid property to FallbackProcess for consistent interface - Add proper type annotations (Process | FallbackProcess) - Replace existing termination logic with new unified approach This addresses issues from PRs #850 (npx child processes) and #729 (Windows process trees) in a unified, dependency-free way. Reported-by:surya-prakash-susarla Reported-by:jingx8885 Github-Issue:#547
- test_stdio_client_child_process_cleanup: Verifies that child processes spawned by the parent (like npx spawning node) are properly terminated - test_stdio_client_nested_process_tree: Tests that deeply nested process trees (parent -> child -> grandchild) are all terminated - test_stdio_client_early_parent_exit: Tests the race condition where parent exits during cleanup but children are still terminated via process group These tests verify the fix works correctly across different subprocess spawning scenarios without requiring external dependencies like psutil.
Replace platform-specific commands (ping/sleep) with a Python script to ensure consistent behavior across all platforms. Also adjust timing expectations to account for the full shutdown sequence on Windows: - 2 seconds waiting for stdin closure response - 2 seconds waiting for terminate() to complete - Plus overhead This prevents the test from timing out on Windows while still properly testing the cleanup mechanism.
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Motivation and Context
#555, #559, #765 address important but different ways MCP servers can hang if they don't respect SIGTERM or SIGINT.
This PR adds regressions tests to clearly demonstrate the edge cases addressed.
How Has This Been Tested?
New regression tests added (each fails without the relevant fix)
For #555 and #559:
For #765:
Breaking Changes
None.
Types of changes
Checklist
Additional context