pyobjc-dev

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

[Ratko J. <rja...@gm...>]

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...


(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.



Also, how does one compile svn trunk properly??? "easy_install pyobjc"
downloads a new version when I want it to compile my modified version. Right
now I have a serious hack... the whole 2.2b2 from easy_install + Quartz
compiled separately from svn (2.2b3).


Some system info:Mac OS X 10.5.7
Apple Python 2.5
built-in PyObjC (also tried PyObjC 2.2b2)


-Ratko

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

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

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...
>
>
> (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.

Thanks for the bugreport.

>
>
>
> Also, how does one compile svn trunk properly??? "easy_install  
> pyobjc" downloads a new version when I want it to compile my  
> modified version. Right now I have a serious hack... the whole 2.2b2  
> from easy_install + Quartz compiled separately from svn (2.2b3).

This should work just fine. Building the entire trunk is not very  
convenient at the moment, there is a script for rebuilding everything  
at the toplevel in the repository (that is, the directory that also  
contains pyobjc-core). This script runs 'python setup.py develop' on  
all subprojects.

Ronald

>
>
> Some system info:
> Mac OS X 10.5.7
> Apple Python 2.5
> built-in PyObjC (also tried PyObjC 2.2b2)
>
>
> -Ratko
> ------------------------------------------------------------------------------
> _______________________________________________
> Pyobjc-dev mailing list
> Pyo...@li...
> https://lists.sourceforge.net/lists/listinfo/pyobjc-dev

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