在啟動另一個塊之前等待直到執(zhí)行兩個異步塊使用GCD時，我們希望等到兩個異步塊執(zhí)行完成后再繼續(xù)執(zhí)行下一步。最好的方法是什么？我們嘗試了以下方法，但它似乎不起作用：dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ { // block1});dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ { // block2});// wait until both the block1 and block2 are done before start block3// how to do that?dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ { // block3});
3 回答
守著一只汪
TA貢獻1872條經(jīng)驗 獲得超4個贊
使用調(diào)度組：看到這里的一個例子，在蘋果的iOS開發(fā)者庫的并發(fā)編程指南“調(diào)度隊列”章“等待上排隊任務(wù)組”
您的示例可能如下所示：
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
// block1
NSLog(@"Block1");
[NSThread sleepForTimeInterval:5.0];
NSLog(@"Block1 End");
});
dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
// block2
NSLog(@"Block2");
[NSThread sleepForTimeInterval:8.0];
NSLog(@"Block2 End");
});
dispatch_group_notify(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
// block3
NSLog(@"Block3");
});
// only for non-ARC projects, handled automatically in ARC-enabled projects.
dispatch_release(group);
并可以產(chǎn)生這樣的輸出：
2012-08-11 16:10:18.049 Dispatch[11858:1e03] Block1
2012-08-11 16:10:18.052 Dispatch[11858:1d03] Block2
2012-08-11 16:10:23.051 Dispatch[11858:1e03] Block1 End
2012-08-11 16:10:26.053 Dispatch[11858:1d03] Block2 End
2012-08-11 16:10:26.054 Dispatch[11858:1d03] Block3
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