[pywin32-bugs] [ pywin32-Bugs-906305 ] Problems (deadlock) with calling CEnterLeavePython.acquire

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Bugs item #906305, was opened at 2004-02-28 12:44
Message generated for change (Settings changed) made by mhammond
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=551954&aid=906305&group_id=78018

Category: win32
Group: None
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Greg Chapman (glchapman)
Assigned to: Nobody/Anonymous (nobody)
Summary: Problems (deadlock) with calling CEnterLeavePython.acquire

Initial Comment:
PyWndProcHWND in win32gui explicitly calls the 
acquire method of _celp (a CEnterLeavePython 
instance) when handling a WM_NCDESTROY message.  
Unfortunately, if this message was not handled by 
PyWndProc_Call, _celp.release will already have been 
called (just prior to dispatching to oldWndProc), setting 
_celp.released to TRUE.  Because released == TRUE, 
_celp's destructor does not release the GIL, with a 
deadlock likely to result.  (In my case it did result, 
since the WM_NCDESTROY was produced by a call to 
win32gui.DestroyWindow).

Perhaps released should be set in the acquire method 
rather than in the constructor?

I'm using win32all build 200, Python 2.3.3, and 
Windows XP.


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>Comment By: Mark Hammond (mhammond)
Date: 2004-04-07 15:25

Message:
Logged In: YES 
user_id=14198

This bug was recently fixed and will be in the next release.

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Comment By: Greg Chapman (glchapman)
Date: 2004-02-28 14:49

Message:
Logged In: YES 
user_id=86307

I just realized that, even if PyWndProc_Call handles 
WM_NCDESTROY, there is still likely to be a deadlock.  In 
that case, _celp.acquire (and thus PyGILState_Ensure) will 
be called twice, first by the constructor and second by the 
explicit call.  The second call will overwrite _celp.state with 
PyGILState_LOCKED.  When _celp's destructor is called, 
PyGILState_Release will not try to release the GIL even if the 
first call to PyGILState_Ensure returned 
PyGILState_UNLOCKED.

If I understand correctly, CEnterLeavePython.acquire should 
probably look like:

void acquire(void) {
    if (released) {
        state = PyGILState_Ensure();
        released = FALSE;
    }
}

// also need:

CEnterLeavePython() {
    released = TRUE;
    acquire();
}


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