Question

OK, I have a memory management problem that is driving me up a wall. At one point I swear this worked with no problems, but now it’s leaking memory everywhere and I can’t figure out why.

To begin with I’m starting an NSTask and then running a loop while the task is running.

 NSTask *encodingTask = [[NSTask alloc] init];
            NSFileHandle *taskStdout = [NSFileHandle fileHandleForWritingAtPath:encodingOutput];
            [encodingTask setStandardOutput:taskStdout];
            [encodingTask setStandardError:taskStdout];
NSString argString = [NSString stingWithString: @"some arguments"];
[encodingTask setArguments:taskArgs];
            [encodingTask setLaunchPath:somePath];
            [encodingTask launch];

while ([encodingTask isRunning]){
                sleep(1);
                [self encodeProgressTimer];
            }

The encodeProgessTimer method is grabbing the last line from the stdOut and placing that in the menu bar:

- (void)encodeProgressTimer
{
    if ([[NSUserDefaults standardUserDefaults] boolForKey:@"menuProgress"]) {
    // Read the last line
 NSString *fileData = [NSString stringWithContentsOfFile:encodingOutput encoding:NSASCIIStringEncoding error:nil];
    NSArray *lines = [fileData componentsSeparatedByString:@"\r"];
    NSString *lastLine = [lines objectAtIndex:[lines count] - 1];
    NSString *percent;
    NSString *eta;
    BOOL dataFound = NO;
    if ([lastLine length] == 71) {
        dataFound = YES;
        percentRange = (NSRange) {23,5};
        etaRange = (NSRange) {61,9};
        percent = [lastLine substringWithRange:percentRange];
        eta = [lastLine substringWithRange:etaRange];
    }
    else if ([lastLine length] == 72) {
        dataFound = YES;
        percentRange = (NSRange) {23,5};
        etaRange = (NSRange) {62,9};
        percent = [lastLine substringWithRange:percentRange];
        eta = [lastLine substringWithRange:etaRange];
    }
    else if ([lastLine length] == 70) {
        dataFound = YES;
        percentRange = (NSRange) {23,5};
        etaRange = (NSRange) {60,9};
        percent = [lastLine substringWithRange:percentRange];
        eta = [lastLine substringWithRange:etaRange];
    }

    if (dataFound) {
        NSMutableString *bottomStr = [[NSMutableString alloc] 
                                  initWithFormat:@"Encoding: %@%% - ETA %@", percent, eta];
                [appDelegate setMenuTop:topString andBottom:bottomStr];
        [bottomStr release];
    }

}

}

It’s my understanding that anything I’m not specifically allocating and initializing should be auto released when the method has completed, but that isn’t the case. Memory usage goes up exponentially every second when this is called. If I look at my memory allocations the number of living CFstings goes through the roof. If I turn of encodeProgressTimer my problems go away. I tried adding an autorelease pool to encodeProgressTimer which made memory usage very stable, however after 20 minutes or so of running I get a EXC_BAD_ACCESS. Turning on Zombies turns that into:

*** -[NSConcreteAttributedString _drawCenteredVerticallyInRect:scrollable:]: message sent to deallocated instance 0x2bc756e0

I actually went through and changed each variable declaration into it’s alloc/init counterpart and manually released them, but that didn’t solve the problem either. At this point I’m pretty stumped.

Also for the sake of completeness the [appDelegate setMenuTop: andBottom:] method looks like this:

-(void) setMenuTop: (NSString *) top andBottom: (NSString *) bottom
{  
if ([[NSUserDefaults standardUserDefaults] boolForKey:@"menuProgress"]) {
    [statusItem setImage:nil];
    NSMutableParagraphStyle *lineHeight = [[NSMutableParagraphStyle alloc] init];
    [lineHeight setMaximumLineHeight:10.5];
    [lineHeight setLineBreakMode:NSLineBreakByTruncatingMiddle];
    OperationQueue *opQueue = [OperationQueue sharedQueue];
    NSString *sBuffer = [[NSMutableString alloc] initWithFormat: @"%@ (%i More)\n%@", top, [opQueue queueCount] - 1, bottom];
    attributes = [[NSDictionary alloc] initWithObjectsAndKeys:[NSFont menuFontOfSize:9], NSFontAttributeName, lineHeight, NSParagraphStyleAttributeName, nil];
    if (statusTitle)
        [statusTitle release];
    statusTitle = [[NSAttributedString alloc] initWithString: sBuffer  attributes: attributes];
    [statusItem setAttributedTitle: statusTitle];
    [lineHeight release];
    [sBuffer release];
    [attributes release];
    }

}

Answer 1

There will be loads of stuff in the autorelease pool, but you need to explicitly drain it for the memory to go away. Change your while loop as follows:

while ([encodingTask isRunning]){
   NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
   sleep(1);
   [self encodeProgressTimer];
   [pool drain];
}

Other stuff: if you are running this on a thread, you can’t update user interface items directly. You need to use something like performSelectorOnMainThread: to actualy update the UI. If you are not running this on a thread, you need to rethink your design. The whole UI of your application will freeze while the loop is running.