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|Python and Prolog deadlocks
In a threaded environment, Python calls must be guarded by PyGILState_Ensure() and PyGILState_Release() that ultimately lock/unlock a mutex. Unfortunately there is no PyGILState_TryEnsure() and therefore we may create deadlocks when Prolog locks are involved. This may either apply to explicit Prolog locks from with_mutex/2 and friends or implicit locks on e.g. I/O streams. The classical scenario is thread A holding the Python GIL and wanting to call Prolog code that locks a mutex M, while thread B holds M and wishes to make a Python call and this tries to lock the GIL. The predicate py_gil_owner/1 can be used to help diagnosing such issues.