Operation Queue with in block cancellation

block_op.m

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{
  @autoreleasepool
	{
		NSOperationQueue *queue = [[NSOperationQueue alloc] init];
		queue.maxConcurrentOperationCount = 1;
		
		__block NSBlockOperation *operation = [[NSBlockOperation alloc] init];
		[operation addExecutionBlock:^{
			NSLog(@"block operation started");
			for (int i = 10; i > 0; --i)
			{
				if (operation.isCancelled)
				{
					NSLog(@"block operation cancelled");
					return;
				}
				sleep(2);
				NSLog(@"block running %d", i);
			}
			NSLog(@"block operation ended");
		}];
		[queue addOperation:operation];
		
		sleep(8);
		NSLog(@"Cancelling all operations");
		[queue cancelAllOperations];
		[queue waitUntilAllOperationsAreFinished];
    }
    return 0;
}