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Title: Fix: Prevent session manager shutdown on individual session crash by soby · Pull Request #841 · modelcontextprotocol/python-sdk · GitHub

Open Graph Title: Fix: Prevent session manager shutdown on individual session crash by soby · Pull Request #841 · modelcontextprotocol/python-sdk

X Title: Fix: Prevent session manager shutdown on individual session crash by soby · Pull Request #841 · modelcontextprotocol/python-sdk

Description: Previously, an unhandled exception within a single MCP session's MCPServer.run() task could propagate to the StreamableHTTPSessionManager's main task group. This would cause the entire task group to cancel, effectively shutting down the session manager and terminating all active sessions. This commit addresses the issue by: Wrapping the self.app.run(...) call within the run_server (for stateful requests) and run_stateless_server (for stateless requests) inner functions in StreamableHTTPSessionManager with a try...except Exception block. Logging any caught exceptions along with the session ID (for stateful requests) to aid in debugging the crashed session. This change ensures that if a single session encounters an unexpected error and crashes, it only affects that specific session. The StreamableHTTPSessionManager will continue to run, and other active sessions will remain operational. This significantly improves the robustness and availability of the server. Motivation and Context Unhandled exceptions such as a network error would render the server unusable until restart How Has This Been Tested? Yes, specifically by generating client disconnects and observing the server log the unhandled error but remain running and stable Breaking Changes No breaking changes Types of changes Bug fix (non-breaking change which fixes an issue) New feature (non-breaking change which adds functionality) Breaking change (fix or feature that would cause existing functionality to change) Documentation update Checklist I have read the MCP Documentation My code follows the repository's style guidelines New and existing tests pass locally I have added appropriate error handling I have added or updated documentation as needed Additional context

Open Graph Description: Previously, an unhandled exception within a single MCP session's MCPServer.run() task could propagate to the StreamableHTTPSessionManager's main task group. This would cause the entire task...

X Description: Previously, an unhandled exception within a single MCP session's MCPServer.run() task could propagate to the StreamableHTTPSessionManager's main task group. This would cause the ent...

Opengraph URL: https://github.com/modelcontextprotocol/python-sdk/pull/841

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722ff23 Fix: Prevent session manager shutdown on individual session crash soby May 29, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/722ff236487dfff8d027187fe49ca9b7c383334e
415fa19 only remove error sessions and not those that have not been terminated soby May 29, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/415fa191ea6144f48501bd7582aca6f1f68a7747
be47a85 lint soby May 29, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/be47a85821b307fa4ed87cec2e7b8874eded535b
0d477c4 step down logging from error to warning soby Jun 2, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/0d477c4000fb6f63c4d55f2a5d9e8146475980dc
68fc9ca step down logging for other places subject to network closures/discon… soby Jun 4, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/68fc9ca7ce39220484d4d2c7142996830e4507c1
615336a ruff soby Jun 15, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/615336a5bf4b6018506c2617d7c21b55d721de84
8359301 linter differences of opinion soby Jun 15, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/83593015fa316ca01fc88f569013d614ac9168d7
ec245fd Apply review feedback felixweinberger Jul 8, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/ec245fdff96d5e19c1e9b77cf25557a0098f700e
0cb1f05 Update src/mcp/server/streamable_http_manager.py soby Jul 9, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/0cb1f05ff1cccfdc8276257c7312e5392d140a80
635ab04 Merge branch 'main' into fix/session-manager-resilience soby Jul 9, 2025 https://github.com/modelcontextprotocol/python-sdk/pull/841/commits/635ab0453f1ec90493132ec70f69c92381bdd241
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