小编Jim*_*mmy的帖子

考虑以下代码：

@interface ViewController ()
@property (nonatomic, strong) dispatch_source_t source;
@end

@implementation ViewController

-(void)viewDidLoad {
    [super viewDidLoad];

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    self.source = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    self.source = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    dispatch_resume(self.source);
    dispatch_source_set_timer(self.source, dispatch_time(DISPATCH_TIME_NOW, 0.2 * NSEC_PER_SEC), 0.2 * NSEC_PER_SEC, 0.1 * NSEC_PER_SEC);
    dispatch_source_set_event_handler(self.source, ^{
        NSLog(@"%s",__func__);
    });
}

@end

如果我使用dispatch_source_create创建相同的DISPATCH_SOURCE_TYPE_TIMER两次，应用程序将崩溃。为什么？

像上面的例子一样创建一次和两次调度源有什么区别吗？

libdispatch.dylib`_dispatch_xref_dispose:
    0x10015e174 <+0>:  ldr    w8, [x0, #48]
    0x10015e178 <+4>:  cmp    w8, #2                    ; =2 
    0x10015e17c <+8>:  b.hs   0x10015e184               ; <+16>
    0x10015e180 <+12>: ret …