Question

I wrote a method(getDirTree1) that makes listing all directories from the root, using the recommended class NSDirectoryEnumerator and method nextObject. But while it was running unacceptably used a lot of memory (mainly private class NSPathStore2):

-(void) getDirTree1:(NSString*)directoryPath {
    NSDirectoryEnumerator *dirEnum = [self->fileManager enumeratorAtPath:derectoryPath];
    NSString *filePath;
    NSString *fullFilePath;

    while ( ( filePath = [ dirEnum nextObject ] ) != nil ) {
        fullFilePath = [ directoryPath stringByAppendingPathComponent:filePath ];
        NSLog( @"%@ \n", fullPath ); 
}

}

Assuming that this is because the object NSDirectoryEnumerator, I rewrote the method(getDirTree2). Now using the recursion, NSArray class and objectEnumerator method.
But once again used a lot of memory.

-(void) getDirTree2:(NSString*)directoryPath {
   NSArray *contents = [ self->fileManager contentsOfDirectoryAtPath:directoryPath error:NULL ];
   NSEnumerator *enumeratorContent [ contents objectEnumerator ];
   NSString *file;
   BOOL fileIsDirectory = FALSE;

   while ( ( file = [ enumeratorContent nextObject ] ) ) {
       NSLog( @"%@ \n", [ directoryPath stringByAppendingPathComponent: file ] );
       if ( [ self->fileManager fileExistAtPath:[ directoryPath stringByAppendingPathComponent:file ] isDirectory:&fileIsDirectory ] && fileIsDirectory )
           [ self getDirTree2:[ directoryPath stringByAppendingPathComponent: file ] ];
   }
}

What I missed(maybe I must dealloc/retain some objects) and how to do better.
Thanks.

Answer 1

[directoryPath stringByAppendingPathComponent:filePath]; returns an autoreleased object. Since it’s happening inside such a tight loop, all these objects are adding up and causing the large memory footprint in question. All you have to do to fix it is get rid of them more often. You can change your method to something that doesn’t use autorelease, or you could just create your own, tight autorelease pool, like this:

while ( ( filePath = [ dirEnum nextObject ] ) != nil ) {
    NSAutoreleasePool* pool = [NSAutoreleasePool new];
    fullFilePath = [ directoryPath stringByAppendingPathComponent:filePath ];
    NSLog( @"%@ \n", fullPath );
    [pool drain];
}

This will ensure that everything’s released as soon as you no longer need it, avoiding the buildup of objects during the loop.

(Interesting sidenote: NSPathStore2 is a private class related to NSString (which is a class cluster) used to store path-type strings. That’s how I knew which method was at fault.)