概念
同步: 阻塞当前线程的执行。(dispatch_sync)
异步: 不会阻塞当前线程的执行。(dispatch_async)
串行队列:
并行队列:
</br>
队列分为两类，串行队列和并行对列
串行队列，不能同步执行，不然会发现死锁
原因分析, 阻塞当前线程，在当前线程执行代码块，然后再继续执行当前线程的别的代码。可是当前线程已被阻塞，代码块无法执行。当前线程中的其余代码也无法执行。
总结:
| 串行 | 并行 | |
|---|---|---|
| 同步 | 死锁 (1) | 线程:当前; 阻塞: 是 (2) |
| 异步 | 线程: 队列对应线程; 阻塞: 否 (3) | 线程: 创建新的线程; 阻塞: 否 (4) |
对应线程: dispatch_get_main_queue对应的是主线程
dispatch_queue_create 对应别的线程
当前线程: 默认在主线程或在用并行队列异步执行产生的新线程
事例代码(对应表格中的编号)
(1)
(2)
let myQueue = dispatch_queue_create("lyhux_queue", DISPATCH_QUEUE_CONCURRENT)
let globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
let mainQueue = dispatch_get_main_queue()
NSLog("之前 --%@", NSThread.currentThread())
dispatch_async(myQueue, {() -> Void in
NSLog("My queue async --%@", NSThread.currentThread())
dispatch_sync(globalQueue, {() -> Void in
NSLog("global sync --%@", NSThread.currentThread())
})
dispatch_sync(globalQueue, {() -> Void in
NSLog("global sync --%@", NSThread.currentThread())
})
dispatch_sync(globalQueue, {() -> Void in
NSLog("global sync --%@", NSThread.currentThread())
})
dispatch_sync(globalQueue, {() -> Void in
NSLog("global sync --%@", NSThread.currentThread())
})
dispatch_sync(globalQueue, {() -> Void in
NSLog("global sync --%@", NSThread.currentThread())
})
})
NSLog("之后 --%@", NSThread.currentThread())
(3)
let myQueue = dispatch_queue_create("lyhux_queue", DISPATCH_QUEUE_SERIAL)
let globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
let mainQueue = dispatch_get_main_queue()
NSLog("之前 --%@", NSThread.currentThread())
dispatch_async(globalQueue, {() -> Void in
NSLog("global async --%@", NSThread.currentThread())
dispatch_async(myQueue, {() -> Void in
NSLog("What thread: %@", NSThread.currentThread())
dispatch_async(mainQueue, {() -> Void in
NSLog("Main thread: %@", NSThread.currentThread())
})
})
})
dispatch_async(globalQueue, {() -> Void in
NSLog("global 2 async --%@", NSThread.currentThread())
dispatch_async(myQueue, {() -> Void in
NSLog("What thread 2: %@", NSThread.currentThread())
dispatch_async(mainQueue, {() -> Void in
NSLog("Main thread 2 : %@", NSThread.currentThread())
})
})
})
dispatch_async(globalQueue, {() -> Void in
NSLog("global 3 async --%@", NSThread.currentThread())
dispatch_async(myQueue, {() -> Void in
NSLog("What thread 3: %@", NSThread.currentThread())
dispatch_async(mainQueue, {() -> Void in
NSLog("Main thread 3 : %@", NSThread.currentThread())
})
})
})
NSLog("之后 --%@", NSThread.currentThread())
(4)
有错误欢迎指正，拍砖
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