GCD中线程和队列之间的关系是什么？

问题描述

1. 一个线程只包含一个队列吗？


2. 如果我将一个块异步调度到globalQueue，它是否可以在主线程上运行？


3. 什么样的情况会导致 dispatch_sync 死锁？

1. does one thread only contain one queue?
2. if I dispatch a block asynchronously to globalQueue ,can it run on main thread by any chance?
3. what kind of situation will cause dispatch_sync to dead lock?

推荐答案

1。一个线程只包含一个队列吗？

1. Does one thread only contain one queue?

这种关系是一种方式。串行队列可以保存一个线程来执行分派给它的块，但是线程不知道队列。好吧，主线程是特殊的，它知道主队列。

The relationship is one way. Serial queue may hold a thread to execute the block dispatched to it, but thread doesn't know a queue. Well, main thread is special, it knows the main queue.

我的猜测

My guess

调度队列没有指示它将运行块或函数的线程，我认为调度队列管理包含许多线程的线程池，它将在调度块时获取一个空闲线程。所以一个线程可以在一段时间内用于许多调度队列。

Dispatch queue doesn't indicate which thread it will run block or function on, I think dispatch queue manages a thread pool which contains many thread, it will fetch one idle thread when a block is dispatched. So one thread may work for many dispatch queue in a period time.

但是有人认为是肯定的：当你将一个块发送到队列时，这个块的线程正在为一个确定的调度队列运行，您可以使用 dispatch_get_current_queue 来获取它。

But one think is for sure: when you dispatch a block to a queue, the thread which this block is running on works for one determined dispatch queue, you can get it using dispatch_get_current_queue.

2。如果我将一个块异步调度到globalQueue，它是否可以在主线程上运行？

2. If I dispatch a block asynchronously to globalQueue ,can it run on main thread by any chance?

我认为它不会运行任何在主线程上阻塞到globalQueue，因为它无法评估块的执行时间，如果它是一个长时间的工作，它将阻塞主线程。

I think it won't run any block to globalQueue on main thread, because it can't evaluate the execution time of the block, if it is a long time job, it will block the main thread.

的 3。什么样的情况会导致dispatch_sync死锁？

3. what kind of situation will cause dispatch_sync to dead lock?

我引用并发编程指南中的段落

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