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Bug #20587

Updated by ivoanjo (Ivo Anjo) 5 months ago

Hey! I work for Datadog on the Ruby profiler part of the [`datadog` (previously `ddtrace`)](https://github.com/datadog/dd-trace-rb) gem. 

 While I was investigating https://bugs.ruby-lang.org/issues/20586, I spotted that there's a number of cases where, in `dir.c`, blocking system calls are being made (e.g. `readdir()`, ~~`opendir()`~~, ... see comments for more detailed list...) `opendir()`, etc) without releasing the GVL. 

 This means that if they block for a long time (as happens in the gcsfuse example in https://bugs.ruby-lang.org/issues/20586 ), the Ruby VM will just be blocked and not make any progress. 

 The combination of not releasing the GVL + slow system calls actually makes the issue in https://bugs.ruby-lang.org/issues/20586 more likely to happen with the Datadog profiler, although even if the code releases the GVL the underlying issue could still happen, and this is why I decided to file this bug separately.

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