Fix hanging on streams when stdio_client exiting #559
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Triggers a TaskGroup cancel after reaching the finally code block.
LionNatsu
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ihrpr
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Apr 30, 2025
Merged to test_stdio.py
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You're welcome, @ihrpr. Just so you know, all requested changes are resolved :) |
ihrpr
requested changes
May 8, 2025
Use async versions of .close() Co-authored-by: ihrpr <inna.hrpr@gmail.com>
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@ihrpr Resolved |
felixweinberger
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Jun 26, 2025
This commit demonstrates that PR #559's stream cleanup alone is sufficient to prevent hanging, even with servers that ignore SIGTERM. Testing shows: 1. PR #559 stream cleanup alone handles all tested hanging scenarios 2. Timeout mechanism may be unnecessary additional complexity 3. Existing Unix behavior works fine without timeouts 4. Original timeout tests still pass, confirming no regression This simpler approach preserves Unix behavior while eliminating platform-specific timeout handling complexity. 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com>
felixweinberger
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Jun 26, 2025
This commit demonstrates that PR #559's stream cleanup alone is sufficient to prevent hanging, even with servers that ignore SIGTERM. Testing shows: 1. PR #559 stream cleanup alone handles all tested hanging scenarios 2. Timeout mechanism may be unnecessary additional complexity 3. Existing Unix behavior works fine without timeouts 4. Original timeout tests still pass, confirming no regression This simpler approach preserves Unix behavior while eliminating platform-specific timeout handling complexity. 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com>
felixweinberger
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Jun 26, 2025
This change demonstrates a simpler approach than PR #555's timeout mechanism: 1. **Evidence**: Extensive testing shows PR #559 stream cleanup alone prevents hanging, even with servers that ignore SIGTERM and keep streams open. 2. **Simplification**: Removes all timeout logic and Windows-specific termination function in favor of unified `process.terminate()` + stream cleanup. 3. **Benefits**: - Less code complexity (no timeout handling, no platform branching) - Preserves proven stream cleanup protection from PR #559 - Makes behavior consistent across all platforms - All existing timeout tests still pass 4. **Risk reduction**: Avoids changing process termination semantics while maintaining hanging protection through stream cleanup. The core insight: process hanging was caused by stream management issues (solved by PR #559), not termination timing issues (targeted by PR #555).
felixweinberger
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Jun 26, 2025
**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()
felixweinberger
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Jun 26, 2025
**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()
9 tasks
felixweinberger
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Jun 26, 2025
**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.
felixweinberger
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Jun 26, 2025
**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.
9 tasks
felixweinberger
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Jun 26, 2025
**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.
felixweinberger
added a commit
that referenced
this pull request
Jun 26, 2025
**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.
felixweinberger
added a commit
that referenced
this pull request
Jun 26, 2025
**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.
felixweinberger
added a commit
that referenced
this pull request
Jun 26, 2025
**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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Triggers a TaskGroup cancel after reaching the finally code block.
Motivation and Context
stdin_writerin the task group hangs when pressing Ctrl+c.Now we explicitly close the streams blocking.
How Has This Been Tested?
Tested in a new simple no-op test and a real Uvicorn Starlette application.
Types of changes
Checklist