Re: [Pyobjc-dev] bus error in CGEventTapCreate... found the problem

[Ronald O. <ron...@ma...>]

It has taken me way to long to get around to this, but I finally  
commited a fix for this (revision 2266 and 2267). I still have to  
write a unittest that uses this API, but that can wait.

On 30 Jun, 2009, at 0:38, Ratko Jagodic wrote:

> I am trying to capture some mouse events using CGEventTapCreate and  
> I found out that the following causes a bus error every time:
>
> eventMask = (1<<kCGEventMouseMoved)
> eventTap = CGEventTapCreate(kCGSessionEventTap,  
> kCGHeadInsertEventTap, 0, eventMask, myCGEventCallback)
>
>
> I've traced it down to two problems, both in Quartz framework in  
> _callbacks.m in the function m_CGEventTapCreate:
>
> (1) the function expects 5 inputs and yet it tries to assign 6, last  
> one being "info"... which ends up being an uninitialized pointer.  
> That seems to cause a bus error further down when it tries to create  
> a tuple of "callback" and "info":
>                   PyObject* real_info = Py_BuildValue("OO",  
> callback, info);
> For my purposes, I just changed CGEventTapCreate to accept 6th input  
> when parsing arguments ("OOOOOO"), as it does in carbon. Not sure if  
> that's the right approach...

Adding an extra "O" was the correct fix here.

>
>
> (2) After fixing that, I encountered the next bus error with the  
> line further down in the same function:
>                   CFRelease(retval);
> I have no idea why this is crashing but I just commented it out for  
> now. I am assuming the worst that can happen is a memory leak and  
> considering that I call this only once, I didn't think it was a big  
> problem.

This should have been "if (result) { CFRelease(result); }".

Ronald