fix: prevent 'event loop already running' when async tools run in parallel#2207
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fix: prevent 'event loop already running' when async tools run in parallel#2207
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…allel When the model returns multiple tool calls, run_agent.py executes them concurrently in a ThreadPoolExecutor. Each thread called _run_async() which used a shared persistent event loop (_get_tool_loop()). If two async tools (like web_extract) ran in parallel, the second thread would hit 'This event loop is already running' on the shared loop. Fix: detect worker threads (not main thread) and use asyncio.run() with a per-thread fresh loop instead of the shared persistent one. The shared loop is still used for the main thread (CLI sequential path) to keep cached async clients (httpx/AsyncOpenAI) alive.
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Mar 26, 2026
…allel (NousResearch#2207) When the model returns multiple tool calls, run_agent.py executes them concurrently in a ThreadPoolExecutor. Each thread called _run_async() which used a shared persistent event loop (_get_tool_loop()). If two async tools (like web_extract) ran in parallel, the second thread would hit 'This event loop is already running' on the shared loop. Fix: detect worker threads (not main thread) and use asyncio.run() with a per-thread fresh loop instead of the shared persistent one. The shared loop is still used for the main thread (CLI sequential path) to keep cached async clients (httpx/AsyncOpenAI) alive. Co-authored-by: Test <test@test.com>
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Summary
Fixes
RuntimeError: This event loop is already runningwhen async tools (likeweb_extract) are executed as part of a parallel tool batch.Root cause
When the model returns multiple tool calls,
run_agent.pyruns them concurrently in aThreadPoolExecutor(line 4598). Each worker thread calls_run_async()which used a shared persistent event loop (_get_tool_loop()). If two async tools ran in parallel, the second thread would calltool_loop.run_until_complete()while the first thread was still using it →RuntimeError: This event loop is already running.This only happened when:
web_extract,web_search, etc.)It didn't reproduce in CLI single-tool-at-a-time usage, only in parallel execution.
Fix
Detect worker threads (
threading.current_thread() is not threading.main_thread()) and useasyncio.run()with a per-thread fresh loop instead of the shared persistent one. The shared loop is still used for the main thread (CLI sequential path) to keep cached async clients alive.Test plan