glXMakeCurrent freeze after BadAlloc (CreatePbuff)


i have a problem with my opengl program. I use pbuffers (depending on the user-interaction also a few of them) for offscreen rendering. I had a very “simple” idea: Make Pbuffer creation fail-save even if there is a BadAlloc, i.e. the application should still be usable after a BadAlloc (in glxCreatePbuffer).

The first thing I did was to create a function for the error handler:
In case a BadAlloc occurs, I set a global variable which I check after the glXCreatePbuffer call. The idea is, to handle the bad allocs this way. This works as expected - as long as there are enough resources I can create a Pbuffer and if all resources are used I get the notification by checking the global variable.

<u>After </u> a BadAlloc error I get in trouble if I create a new glContext (the creation works fine) and try to make this new context current:

The creation works fine (At least I could not find a X or GL Error). But the process does not return after the glxMakeCurrent call. There is no SegFault or anything like that, the application just “waits”. I took a deeper look on what’s going on with a Debugger/strace and found a number of getPid() calls.


#0 0x0000002aab8cdab9 in getpid () from /lib64/tls/
#1 0x0000002aa9027690 in glXChannelRectSyncSGIX () from /usr/lib64/
#2 0x0000002aa9026539 in glXChannelRectSyncSGIX () from /usr/lib64/
#3 0x0000002aa902e949 in glXChannelRectSyncSGIX () from /usr/lib64/
#4 0x0000002aa901f518 in ?? () from /usr/lib64/
#5 0x0000002aa904d88f in _nv000004gl () from /usr/lib64/
#6 0x0000002aa904d35b in _nv000004gl () from /usr/lib64/
#7 0x0000002aaca0214c in _nv000096gl () from /usr/lib64/
#8 0x0000002aac9b9419 in _nv000111gl () from /usr/lib64/
#9 0x0000002aac9f9fab in _nv000096gl () from /usr/lib64/
#10 0x0000002aacae3d1b in _nv000049gl () from /usr/lib64/
#11 0x0000002aacae432a in _nv000049gl () from /usr/lib64/
#12 0x0000002aacae46df in _nv000049gl () from /usr/lib64/
#13 0x0000002aac9bb6fb in _nv000106gl () from /usr/lib64/
#14 0x0000002aa902820f in glXChannelRectSyncSGIX () from /usr/lib64/
#15 0x0000002aa902bad6 in glXChannelRectSyncSGIX () from /usr/lib64/
#16 0x0000002aa9025ea2 in glXMakeCurrent () from /usr/lib64/

If I start my application a second time (while the other application still waits) then the first application stops waiting and continues running as expected. I used gDebugger to find out which glCommand causes this, it’s a glXCreatePBuffer command (same Display). This glXcreatePBuffer command also fails (there are still all resources used) - but thats okay, the second application acts as expected.

So what I’ve done to solve this problem:
I took a new version of mesa to get an idea of what is going on. Anyway with the mesa-lib the program works fine - there was no resource conflict, so I did not even run in the error handling code. I checked my code with gDEBugger but was not able to find a single gl-error.

My Assumption:
I can only guess what is going wrong in my program. I guess that the BadAlloc call (glXCreatePBuffer) does not “set free/unlock” something (some resource) that is locked inside the glxCreatePBuffer call. But I have no idea what this resource may be. The mesa-code uses a few Lock/UnlockDisplay function - maybe it is something like this, but I am not sure. A new glXCreatePBuffer call (even in a different application) “unlocks” this resource and allows the process to continue.

I use a Linux 64Bit system:
Red Hat Enterprise Linux WS release 3 (Taroon Update 4)
and a nvida gfx-card.
OpenGL vendor string: NVIDIA Corporation
OpenGL renderer string: Quadro FX 1000/AGP/SSE2
OpenGL version string: 2.1.0 NVIDIA 96.31

Any suggestion, link, help, hint is very welcome.

Thank you all

Don’t use pbuffers. Simply your life radically and just use FBOs (framebuffer objects). See:

OpenGL Framebuffer Objects (NVidia, GDC’05)
Framebuffer Object Extension Spec

Thank you very much for the hint. Unfortunately it’s not my decision - I have to fix the pbuffer thing.

My guess is, there is something in the driver (a bug or so). Probably the context becomes invalid after the exception.

Thank you very much for this hint. I will try a new 100.xx nvidia driver soon (currently an older driver is installed).

I do not think that the “exception” made the context invalid. The context I try to make current is a new context, which was created after the “exception”. There is also no context current the time I (try to) make the new context current.

Well, sounds lika a driver bug to me. Try newer drivers, if it still doesn’t work, fill in a bug case to nvidia.

The 100.14 Nvidia driver works as expected (no “freezes” anymore). Thank you all for your help.

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