EXC_BAD_ACCESS with glTexImage2D in GLKViewControl

Question

I have an EXC_BAD_ACCESS at the last line of this code (this code is fired several times per second), but I cannot figure out what is the problem:

[EAGLContext setCurrentContext:_context];
glActiveTexture(GL_TEXTURE0);
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glBindTexture(GL_TEXTURE_2D, _backgroundTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, _outputFrame.cols, _outputFrame.rows, 0, GL_BGRA, GL_UNSIGNED_BYTE, _outputFrame.data);

When debugging I make sure that the texture is created (the id is > 0), output frame has a valid pointer to the data and is a 4 channel matrix. I am inside the drawRect method of a GLKViewController. I think I should not have to bind the framebuffer as it is one of the things that are automated here. It doesn't crash at the first frame, but a few dozens frames later.

Can anybody spot the problem?

UPDATE:

It seems it's because of a race condition on _outputFrame, it's being updated while being read by glTexImage2D. I will try to lock it for read, then report back.

Answer 1

That was the solution indeed (see UPDATE), I fixed it with NSLock. Firstly I swapped the instance variable _outputFrame with a temporary one that gets updated from another thread and used the lock to update the instance variable:

[_frameLock lock];
_outputFrame = temp;
[_frameLock unlock];

Then used the lock when I wanted to read from the instance variable:

glActiveTexture(GL_TEXTURE0);
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glBindTexture(GL_TEXTURE_2D, _backgroundTexture);
[_frameLock lock];
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, _outputFrame.cols, _outputFrame.rows, 0, GL_BGRA, GL_UNSIGNED_BYTE, _outputFrame.data);
[_frameLock unlock];

Answer 2

I just figured out some problem like this after several days.

1. better  avoid rendering  in multi-thread
2. better  render in GLKView with base affect, and don't manually manage framebuffer& render buffer by yourself
3. base effect render raw pixel data like this

My solution:

glTexImage2D(...);
self.baseEffect.texture2d0.envMode = GLKTextureEnvModeReplace;
self.baseEffect.texture2d0.target = GLKTextureTarget2D;
self.baseEffect.texture2d0.name = texture;
self.baseEffect.texture2d0.enabled = YES;
self.baseEffect.useConstantColor = YES;