[Bug]: async_playwright() leaves blocking background task if cancelled quickly #42296

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1. sreegithub89 commented on Aug 18, 2026

   

   Srikanth Nakka (sreegithub89)

   on Aug 18, 2026

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   should/have to be async with async_playwright(): in try block?
2. sattlerc commented on Aug 18, 2026

   

   Christian Sattler (sattlerc)

   on Aug 18, 2026

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   should/have to be async with async_playwright(): in try block?

   No. This raises a CancelledError as expected, which causes the task to be cancelled. The problem is that async_playwright().__aenter__() leaves behind some blocking background task.
3. sreegithub89 commented on Aug 18, 2026

   

   Srikanth Nakka (sreegithub89)

   on Aug 18, 2026

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   import asyncio
   from playwright.async_api import async_playwright
   
   async def run_browser():
       # Using async context manager ensures cleanup even if cancelled
       async with async_playwright() as p:
           browser = await p.chromium.launch()
           page = await browser.new_page()
           await page.goto("https://example.com")
           await browser.close()
   
   async def run():
       task = asyncio.create_task(run_browser())
       await asyncio.sleep(0.01)  # simulate early cancellation
       task.cancel()
       try:
           await task
       except asyncio.CancelledError:
           # Context manager guarantees playwright.stop() is called
           print("Task cancelled safely, no background tasks left.")
   
   asyncio.run(run())
   
   
4. sattlerc commented on Aug 19, 2026

   

   Christian Sattler (sattlerc)

   on Aug 19, 2026

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   That's essentially the same program. Hangs for me.
5. sattlerc commented on Aug 19, 2026

   

   Christian Sattler (sattlerc)

   on Aug 19, 2026

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   The async code doesn't seem easy to understand to me and possibly somewhat brittle.

   One thing that immediately stands out: the Python documentation for create_task says:

   Save a reference to the result of this function, to avoid a task disappearing mid-execution. The event loop only keeps weak references to tasks. A task that isn’t referenced elsewhere may get garbage collected at any time, even before it’s done.

   There seem to be several places where that is not the case. For example, in PlaywrightContextManager.__aenter__:

           loop.create_task(self._connection.run())
6. yury-s commented on Aug 19, 2026

   

   Yury Semikhatsky (yury-s)

   on Aug 19, 2026

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   Cancelling a task that is running a Playwright call is not supported and results in undefined behavior. Documenting this in #42312. If you can reproduce a hang without task.cancel(), please open a new issue.
7. sattlerc commented on Aug 19, 2026

   

   Christian Sattler (sattlerc)

   on Aug 19, 2026

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   Cancelling a task that is running a Playwright call is not supported and results in undefined behavior. Documenting this in #42312. If you can reproduce a hang without task.cancel(), please open a new issue.

   That would be unfortunate. It would mean that running playwright as a task inside a TaskGroup is undefined behaviour. This is how I found this issue: starting playwright in parallel with some other task that failed.
8. Yury Semikhatsky (yury-s)

   closed this as completedin #42312on Aug 19, 2026