Asynchronous texture loading iPhone OpenGL ES 2

Question

I'm creating and loading a lot of textures (made of strings). To keep the animation running smoothly, I offload the work to a separate worker thread. It seems to work more or less exactly the way I want, but on older devices (iPhone 3GS) I sometimes notice a long (1 sec) lag. It only occurs sometimes. Now I'm wondering if I'm doing this correctly or if there is any conceptual issue. I paste the source code below.

I should also mention that I do not want to use the GLKit TextureLoader because I also want to offload the texture generating work to the other thread, not just the loading part.

In case you're wondering what I need these textures for, have a look at this video: http://youtu.be/U03p4ZhLjvY?hd=1

NSLock*                     _textureLock;
NSMutableDictionary*        _texturesWithString;
NSMutableArray*             _texturesWithStringLoading;

// This is called when I request a new texture from the drawing routine. 
// If this function returns 0, it means the texture is not ready and Im not displaying it.

-(unsigned int)getTextureWithString:(NSString*)string {
    Texture2D* _texture = [_texturesWithString objectForKey:string];
    if (_texture==nil){
        if (![_texturesWithStringLoading containsObject:string]){
            [_texturesWithStringLoading addObject:string];
            NSDictionary* dic = [[NSDictionary alloc] initWithObjectsAndKeys:string,@"string", nil];
            NSThread* thread = [[NSThread alloc] initWithTarget:self selector:@selector(loadTextureWithDictionary:)object:dic];
            thread.threadPriority = 0.01;
            [thread start];
            [thread release];
        }
        return 0;
    }
    return _texture.name;
}

// This is executed on a separate worker thread.
// The lock makes sure that there are not hundreds of separate threads all creating a texture at the same time and therefore slowing everything down. 
// There must be a smarter way of doing that. Please let me know if you know how! ;-)
-(void)loadTextureWithOptions:(NSDictionary*)_dic{
    [_textureLock lock];
    EAGLContext* context = [[SharegroupManager defaultSharegroup] getNewContext];
    [EAGLContext setCurrentContext: context];

    NSString* string = [_dic objectForKey:@"string"];
    Texture2D* _texture = [[Texture2D alloc] initWithStringModified:string];

    if (_texture!=nil) {
        NSDictionary* _newdic = [[NSDictionary alloc] initWithObjectsAndKeys:_texture,@"texture",string,@"string", nil];
        [self performSelectorOnMainThread:@selector(doneLoadingTexture:) withObject:_newdic waitUntilDone:NO];
        [_newdic release];
        [_texture release];
    }
    [EAGLContext setCurrentContext: nil];
    [context release];
    [_textureLock unlock];
}

// This callback is executed on the main thread and marks adds the texture to the texture cache. 
-(void)doneLoadingTextureWithDictionary:(NSDictionary*)_dic{
    [_texturesWithString setValue:[_dic objectForKey:@"texture"] forKey:[_dic objectForKey:@"string"]];
    [_texturesWithStringLoading removeObject:[_dic objectForKey:@"string"]];
}

Answer 1

The problem was that too many threads were started at the same time. Now I am using a NSOperationQueue rather than NSThreads . That allows me to set maxConcurrentOperationCount and only run one extra background thread that does the texture loading.