Async - 一个简化 GCD 语法的 swift 库

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

The familiar syntax for GCD is:

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(), 0), {
        println("This is run on the main queue, after the previous block")
    })
})

Async adds syntactic sugar resulting in this:

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

Benefits

Less verbose code
Less code indentation

Support

OS X 10.10+ and iOS 8.0+

Things you can do

Supports the modern queue classes:

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

Chain as many blocks as you want:

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

Store reference for later chaining:

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:

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:

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:

// Cancel blocks not yet dispatched
let block1 = Async.background {
    // Heavy work
    for 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:

let block = Async.background {
    // Do stuff
}

// Do other stuff

block.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.

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)

Known improvements

default is a keyword. Workaround used: default_

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

License

The MIT License (MIT)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.