[swift] Async

Async

https://github.com/duemunk/Async

 

Syntactic sugar in Swift for asynchronous dispatches in Grand Central Dispatch (GCD)

这是一个Swift中GCD的语法糖库。

 

Async sugar looks like this:

Async使用起来就像这样子：

Async.background {println("This is run on the background queue") }.main {println("This is run on the main queue, after the previous block") }

Instead of the familiar syntax for GCD:

替换了下面的这种显示方式：

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), {println("This is run on the background queue")dispatch_async(dispatch_get_main_queue(), {println("This is run on the main queue, after the previous block") }) })

Install

pod 'Async', :git => 'https://github.com/duemunk/Async.git'

 

Benefits

Less verbose code 更少的冗余代码

Less code indentation 更少的缩进风

 

Things you can do

Supports the modern queue classes:

支持常用的queue类：

Async.main {} Async.userInteractive {} Async.userInitiated {} Async.utility {} Async.background {}

Chain as many blocks as you want:

你可以将不同的block链接起来使用：

Async.userInitiated {// 1 }.main {// 2 }.background {// 3 }.main { // 4 }

Store reference for later chaining:

也可以分开使用：

let backgroundBlock = Async.background {println("This is run on the background queue") } // Run other code here... // Chain to reference backgroundBlock.main { println("This is run on the \(qos_class_self().description) (expected \(qos_class_main().description)), after the previous block") }

Custom queues:

自定义queue：

let customQueue = dispatch_queue_create("CustomQueueLabel", DISPATCH_QUEUE_CONCURRENT) let otherCustomQueue = dispatch_queue_create("OtherCustomQueueLabel", DISPATCH_QUEUE_CONCURRENT) Async.customQueue(customQueue) { println("Custom queue") }.customQueue(otherCustomQueue) { println("Other custom queue") }

Dispatch block after delay:

延时执行：

let seconds = 0.5 Async.main(after: seconds) { println("Is called after 0.5 seconds") }.background(after: 0.4) { println("At least 0.4 seconds after previous block, and 0.9 after Async code is called") }

Cancel blocks that aren't already dispatched:

取消没有启动的线程：

// Cancel blocks not yet dispatched let block1 = Async.background {// Heavy workfor i in 0...1000 { println("A \(i)") } } let block2 = block1.background { println("B – shouldn't be reached, since cancelled") } Async.main { // Cancel async to allow block1 to begin block1.cancel() // First block is _not_ cancelled block2.cancel() // Second block _is_ cancelled }

Wait for block to finish – an ease way to continue on current queue after background task:

等待一个block运行结束：

let block = Async.background {// Do stuff }// Do other stuffblock.wait()

 

How does it work

The way it work is by using the new notification API for GCD introduced in OS X 10.10 and iOS 8. Each chaining block is called when the previous queue has finished.

本库使用了 iOS 8 提供的通知 API 来完成相关功能，每一个block都会在上一个block执行完了之后继续执行：

let previousBlock = {} let chainingBlock = {} let dispatchQueueForChainingBlock = ... // Use the GCD API to extend the blocks let _previousBlock = dispatch_block_create(DISPATCH_BLOCK_INHERIT_QOS_CLASS, previousBlock) let _chainingBlock = dispatch_block_create(DISPATCH_BLOCK_INHERIT_QOS_CLASS, chainingBlock) // Use the GCD API to call back when finishing the "previous" block dispatch_block_notify(_previousBlock, dispatchQueueForChainingBlock, _chainingBlock)

The syntax part of the chaining works by having class methods on the Async object e.g. Async.main {} which returns a struct. The struct has matching methods e.g. theStruct.main {}.

 

Known bugs

Modern GCD queues don't work as expected in the iOS Simulator. See issues 13, 22.

 

Known improvements

The dispatch_block_t can't be extended. Workaround used: Wrap dispatch_block_t in a struct that takes the block as a property.

 

Bonus stuff

There is also a wrapper for dispatch_apply() for quick parallelisation of a for loop.

Apply.background(100) { i in// Do stuff e.g. println(i) }

Note that this function returns after the block has been run all 100 times i.e. it is not asynchronous. For asynchronous behaviour, wrap it in a an Async block like Async.main{ Apply.background(100) { ... } }.

 

 

 

转载于:https://www.cnblogs.com/YouXianMing/p/4890645.html

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