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Learning 006: SIGTERM in an asyncio process must cancel the main task, not raise ​

  • Date: 2026-10-10
  • Source: system-feedback
  • Work item: issue-17

What happened ​

Embedded Temporal runs as a child process that the harness has to stop in a finally. Two obvious SIGTERM strategies both left it running:

  • A signal.signal handler raising KeyboardInterrupt made asyncio cancel every task at once, the Temporal worker's pollers included. The worker's shutdown then hung.
  • Installing no handler let uvicorn, which takes SIGTERM over while it serves, restore the default action and re-raise the signal after its own shutdown. That killed the process before the finally ran.

Only tests that sent a real SIGTERM to a real subprocess and then looked for the child caught either case.

Learning ​

In an asyncio process, handle SIGTERM with loop.add_signal_handler(SIGTERM, main_task.cancel), which is what asyncio itself does for SIGINT. Install it in every entry point that owns a child process, not only in the CLI. Prove it with a subprocess test that signals and then asserts no child remains.

Action ​

tiny_harness/service/signals.py (cancel_on_sigterm), used by the CLI and by service.serve. tests/integration/embedded/test_cli_embedded.py covers both paths.