main.m

#import <Foundation/Foundation.h>

@interface LBRObject : NSObject
@end

@implementation LBRObject

- (void)execute
{
    @synchronized(self) {
        NSLog(@"1) %@", [NSThread currentThread]);
        dispatch_queue_t queue = dispatch_queue_create("com.lucabernardi.serial_queue", DISPATCH_QUEUE_SERIAL);
        dispatch_sync(queue, ^{
            @synchronized(self) {
                NSLog(@"2) %@", [NSThread currentThread]);
            }
        });
    }
}

@end


int main(int argc, const char * argv[])
{
    @autoreleasepool {
        LBRObject *obj = [LBRObject new];
        [obj execute];
    }
    return 0;
}