问正确使用中央调度-启动、挂起、恢复、取消线程？

EN

#import "ViewController.h"
#import "SVProgressHUD.h"
#import "Queue.h"

@interface ViewController (){
    Queue* queue;
}

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    queue = [[Queue alloc] init];

    UIButton* startbutton = [UIButton buttonWithType:UIButtonTypeRoundedRect]; 
    [startbutton setTitle:@"Start Queue" forState:UIControlStateNormal];
    [startbutton addTarget:self action:@selector(startQueueButton:) forControlEvents:UIControlEventTouchUpInside];
    [startbutton setFrame:CGRectMake(100, 200, 100, 70)];
    [self.view addSubview:startbutton];


    UIButton* suspendbutton = [UIButton buttonWithType:UIButtonTypeRoundedRect]; 
    [suspendbutton setTitle:@"Stop Queue" forState:UIControlStateNormal];
    [suspendbutton addTarget:self action:@selector(suspendQueueButton:) forControlEvents:UIControlEventTouchUpInside];
    [suspendbutton setFrame:CGRectMake(250, 200, 100, 70)];
    [self.view addSubview:suspendbutton];

    UIButton* resumebutton = [UIButton buttonWithType:UIButtonTypeRoundedRect]; 
    [resumebutton setTitle:@"Resume Queue" forState:UIControlStateNormal];
    [resumebutton addTarget:self action:@selector(resumeQueueButton:) forControlEvents:UIControlEventTouchUpInside];
    [resumebutton setFrame:CGRectMake(400, 200, 170, 70)];
    [self.view addSubview:resumebutton];

    UIButton* cancelbutton = [UIButton buttonWithType:UIButtonTypeRoundedRect]; 
    [cancelbutton setTitle:@"Cancel Queue" forState:UIControlStateNormal];
    [cancelbutton addTarget:self action:@selector(cancelQueueButton:) forControlEvents:UIControlEventTouchUpInside];
    [cancelbutton setFrame:CGRectMake(600, 200, 170, 70)];
    [self.view addSubview:cancelbutton];

}

-(void) startQueueButton:(UIButton*) button{    
    NSLog(@"---> startQueueButton");
    [queue start];
}

-(void) suspendQueueButton:(UIButton*) button{
    NSLog(@"---> suspendQueueButton");
    [queue suspend];
}


-(void) resumeQueueButton:(UIButton*) button{
    NSLog(@"---> resumeQueueButton");
    [queue resume];
}

-(void) cancelQueueButton:(UIButton*) button{
    NSLog(@"---> cancelQueueButton");
    [queue cancel];
}



- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return YES;
}

@end

#import "Queue.h"
#import "SVProgressHUD.h"

@interface Queue (){
    dispatch_queue_t queue;
}

@end

@implementation Queue


-(void) start{
    NSLog(@"Queue - start");    

    int count = 1000;

     // SERIAL QUEUE ======================================
     // =======================================================================

    queue = dispatch_queue_create("com.jf.TestQueue", NULL);

    [SVProgressHUD showWithStatus:@"Rendering..."];


    for(int i = 0; i < count; i++) 
    {
        dispatch_async(queue, ^{

            NSLog(@"--> ASYNC %d", i);

           // rendering complete, get back to main queue
           dispatch_async(dispatch_get_main_queue(), ^
              {
                 NSLog(@"--> Image rendered: %d", i);

                  if (i == count-1) {
                      NSLog(@"EndRenderingQueue");

                      [SVProgressHUD dismiss];
                  }
              });
        });
    }

    dispatch_release(queue);    // even under ARC we have to release it    
}


-(void) suspend{

    NSLog(@"Queue - suspend");

    if (queue) {
        NSLog(@"___suspend");
        dispatch_suspend(queue);
    }
}

-(void) resume{
    NSLog(@"Queue - resume");
    if (queue) {
        dispatch_resume(queue);
    }
}
-(void) cancel{
    NSLog(@"Queue - cancel");

    if (queue) {
        dispatch_suspend(queue);
        //dispatch_release(queue);  // if it´s uncommented, it crashes. How to release it securely?
        queue = nil;

        [SVProgressHUD dismiss];

    }

}

@end