Symptom
An agent run with run_sync sometimes hangs forever when its output function calls a second agent with run_sync.
Evidence what you'll see
- Happens only some of the time
- Only in synchronous code
- The second agent is called from a sync output function or tool
Cause
Sync tools and output functions run in worker threads, so the nested run_sync started a second event loop that could deadlock on resources tied to the parent run's loop.
Fix steps
0 of 2 done
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Verify the fix worked
- Run the outer agent many times in a row and confirm every run finishes.
Sources and credit
Summarized in our own words from these public reports. Credit goes to their authors.
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