GCD 线程

dispatch_queue_tqueue =dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);

dispatch_group_tgroup =dispatch_group_create();

dispatch_group_async(group, queue, ^{

[NSThreadsleepForTimeInterval:0];

});

dispatch_group_async(group, queue, ^{

[NSThreadsleepForTimeInterval:.1];

});

dispatch_group_async(group, queue, ^{

[NSThreadsleepForTimeInterval:.3];

});