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我试图了解队列类型之间的差异。据我了解，有3种类型：

  • 全局队列 - 并发 - 无论顺序如何，块都会尽快执行
  • 主队列 - 串行 - 块在提交时执行
  • 私有队列 - 串行

我想知道的是：dispatch_sync 和 dispatch_async 在提交到每种队列时有什么区别？到目前为止，我是这样理解的：

dispatch_sync(global_queue)^
{
     // blocks are executed one after the other in no particular order
     // example: block 3 executes. when it finishes block 7 executes.
}

dispatch_async(global_queue)^
{
     // blocks are executed concurrently in no particular order
     // example: blocks 2,4,5,7 execute at the same time.
}

dispatch_sync(main_queue)^
{
     // blocks are executed one after the other in the order they were submitted
     // example: block 1 executes. when it finishes block 2 will execute and so forth.
}

dispatch_async(main_queue)^
{
     // blocks are executed concurrently in the order they were submitted
     // example: blocks 1-4 (or whatever amount of threads the system can handle at one time) will fire at the same time. 
     // when the first block completes block 5 will then execute.
}

我想知道我对此的看法在多大程度上是正确的。

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1 回答 1

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dispatch_sync 和 dispatch_async 之间的区别有点像 windows API 中的 sendmessage 和 postmessage。dispatch_sync 提交一个块对象以在调度队列上执行并等待该块完成。dispatch_async 在调度队列上提交一个异步执行块并立即返回。

目标队列确定该块是串行调用还是与提交到同一队列的其他块并发调用。独立的串行队列相对于彼此同时处理。

在发布问题之前，您应该先仔细阅读文档。

于 2012-08-04T04:29:00.477 回答