- (void) processImage:(char *)image; ---char* causes a memory leak?

Question

Hello everyone,

in my app I'm trying to process an YUV422 image from a webcam. but I'm getting a huge memory leak. below you can see a sample of simplified code of my app. if I disable the "(m1..." line in the function, there is no leak. (but the images are not being processed). I've tried locks, pools, etc but nothing changed. I'm relatively new to cocoa so all these square brackets look funny/scary to me ;-)
is it a problem with using "char"? in my old linux+c++ app there was no problem. but I was using "unsigned char*", no threads, and I have never checked for leaks...

global:

...
char m [640*480];

"main":

...
[NSThread detachNewThreadSelector:@selector(processOutputBuffer) toTarget:self withObject:nil];
...

function1:

- (void)processOutputBuffer {
[NSThread setThreadPriority:0.4];
[lock lock];
...
Ptr outputBufferBaseAddress = (Ptr)CVPixelBufferGetBaseAddress(outputBuffer);
CVPixelBufferLockBaseAddress(outputBuffer, 0);
[self yuv422_to_y8uv8:outputBufferBaseAddress m1:m];
...
}

function2:

- (void) yuv422_to_y8uv8:(char *)image m1:(char *)m1 {
 int x,y;
 for (y = 0; y < 480; y++)
  for (x = 0; x < 640; x++)
   {
   *(m1 + (640 * y) + (x))=*(image + (640*2 * y) + (x*2)+1);
   }
}

Answer 1

A lame answer... I know. But in case no better answer comes to you. You can always put the function in a C file and make it plain c.

Might even be nice to see if it solves the leak. If not, then the problem lies somewhere else.

Answer 2

if I disable the "*(m1..." line in the function, there is no leak.

Untrue. That's just an assignment. Either there is no leak anyway, or that is not the cause of the leak.

You can use Instruments to look for objects (both plain memory allocations and Cocoa objects) that get leaked, and to diagnose the leaks.

is it a problem with using "char *"?

No. Types do not cause leaks. Incorrect memory management causes leaks.

in my old linux+c++ app there was no problem. but I was using "unsigned char*", no threads, and I have never checked for leaks...

It's possible that you introduced the leak when adding threads, or when adding Cocoa code. It's equally possible that the leak was always there and you never saw it before. Only when you find the problem with Instruments or another tool will you know for sure.

You might also try running the Clang Static Analyzer. It can detect some code patterns that cause leaks, among other things.