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Memory leak log message while *compiling* with Xcode for the iPhone

Answer 1

A:

Most programs will run correctly even with leaks, ... but anyway I don't think you are showing enough information. My guess is that you are sending an object autorelease where there is no pool in place?. lol. Did you try Instruments?

nacho4d 2009-11-06 05:11:40

Answer 2

+1 A:

Those warnings might be because of leaks in the tools themselves. But if not, those kinds of messages are what you see if you run in a thread or perform a selector in the background without setting up an autorelease pool.

Dustin Voss 2009-11-06 05:13:25

Answer 3

+5 A:

In short, the compiler is smarter than you think ;). These errors mean that you are autoreleasing various objects (NSString, NSDictionary, NSNumber) in a context that did not allocate an NSAutoreleasePool. For example, the main.m file of a project should declare an autorelease pool:

int main(int argc, char *argv[]) {

    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    int retVal = UIApplicationMain(argc, argv, nil, nil);
    [pool release];
    return retVal;
}

In many applications this will be the only pool that is ever allocated. Without this pool you can't autorelease anything, and should you try to autorelease it has no pool to go to so it effectively becomes a leak. Check your main function to make sure you have an NSAutoreleasePool being allocated.

There are other situations where you may want to declare another NSAutoreleasePool. The most common situation is when selectors are invoked in a new thread. Every thread must have its own NSAutoreleasePool. For more information on this see the slide 36 of Stanford University CS193P Lecture 10:

- (void)someAction:(id)sender {
    // Fire up a new thread
    [NSThread detachNewThreadSelector:@selector(doWork:) withTarget:self object:someData];
}

- (void)doWork:(id)someData {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    [someData doLotsOfWork];

    // Message back to the main thread
    [self performSelectorOnMainThread:@selector(allDone:) withObject:[someData result] waitUntilDone:NO];
    [pool release];
}

Another example is an expensive loop where you are autoreleasing many objects. Rather than letting the main NSAutoreleasePool grow to an enormous size, you will find that creating a new NSAutoreleasePool every N times around the loop will help keep your resource use to a minimum. Some of this code was also borrowed from the lecture slides listed above:

int N = 10;
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

for (int i = 0; i < someLargeNumber; i++) {
    NSString *string = ...;
    string = [string lowercaseString];
    string = [string stringByAppendingString:...];
    NSLog(@“%@”, string);

    // Release the temporary pool and allocate a new one
    // every N times around the loop

    if (i % N == 0) {
        [pool release];
        pool = [[NSAutoreleasePool alloc] init];
    }
}

[pool release];

Perhaps you have some code like this which is not always allocating or releasing the pools as expected. I'm not sure the compiler is smart enough to notice this type of issue though.

James Wald 2009-11-06 05:36:22

I actually *do* have an autorelease pool allocated before my `UIApplicationMain`; however, it's in a file that's already compiled, and I just link to it with this project. So maybe the compiler's being too smart for its own good?

Jesse Beder 2009-11-06 06:13:34

Hmmm, this seemed to be the problem. I moved the autorelease pool back into the project, and the warnings went away. I guess it was getting confused.

Jesse Beder 2009-11-06 06:29:38

Its possible that its an issue with Xcode itself, I've never tried compiling from the command line so I haven't seen this before. Did you just add the file to your project so you always compile it?

James Wald 2009-11-06 17:43:25

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Memory leak log message while compiling with Xcode for the iPhone

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