Async
Now more than syntactic sugar for asynchronous dispatches in Grand Central Dispatch (GCD) in Swift
Async sugar looks like this:
Async.userInitiated {
10
}.background {
"Score: \($0)"
}.main {
label.text = $0
}
So even though GCD has nice-ish syntax as of Swift 3.0, compare the above with:
DispatchQueue.global(qos: .userInitiated).async {
let value = 10
DispatchQueue.global(qos: .background).async {
let text = "Score: \(value)"
DispatchQueue.main.async {
label.text = text
}
}
}
AsyncGroup sugar looks like this:
let group = AsyncGroup()
group.background {
print("This is run on the background queue")
}
group.background {
print("This is also run on the background queue in parallel")
}
group.wait()
print("Both asynchronous blocks are complete")
Install
Swift Package Manager
Add To Your Project In Xcode 11:
File > Swift Packages > Add Package Dependency
Add As A Dependency In Package.swift:
dependencies: [
.package(url: "https://github.com/duemunk/Async", from: "2.1.0"),
],
CocoaPods
use_frameworks!
pod "AsyncSwift"
Carthage
github "duemunk/Async"
Benefits
- Avoid code indentation by chaining
- Arguments and return types reduce polluted scopes
Things you can do
Supports the modern queue classes:
Async.main {}
Async.userInteractive {}
Async.userInitiated {}
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 {
print("This is run on the background queue")
}
// Run other code here...
// Chain to reference
backgroundBlock.main {
print("This is run on the \(qos_class_self().description) (expected \(qos_class_main().description)), after the previous block")
}
Custom queues:
let customQueue = DispatchQueue(label: "CustomQueueLabel", attributes: [.concurrent])
let otherCustomQueue = DispatchQueue(label: "OtherCustomQueueLabel")
Async.custom(queue: customQueue) {
print("Custom queue")
}.custom(queue: otherCustomQueue) {
print("Other custom queue")
}
Dispatch block after delay:
let seconds = 0.5
Async.main(after: seconds) {
print("Is called after 0.5 seconds")
}.background(after: 0.4) {
print("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 {
print("A \(i)")
}
}
let block2 = block1.background {
print("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)
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.
Apply
There is also a wrapper for dispatch_apply() for quick parallelisation of a for loop.
Apply.background(100) { i in
// Do stuff e.g. print(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.background { Apply.background(100) { ... } }.
AsyncGroup
AsyncGroup facilitates working with groups of asynchronous blocks.
Multiple dispatch blocks with GCD:
let group = AsyncGroup()
group.background {
// Run on background queue
}
group.utility {
// Run on utility queue, in parallel to the previous block
}
group.wait()
All modern queue classes:
group.main {}
group.userInteractive {}
group.userInitiated {}
group.utility {}
group.background {}
Custom queues:
let customQueue = dispatch_queue_create("Label", DISPATCH_QUEUE_CONCURRENT)
group.custom(queue: customQueue) {}
Wait for group to finish:
let group = AsyncGroup()
group.background {
// Do stuff
}
group.background {
// Do other stuff in parallel
}
// Wait for both to finish
group.wait()
// Do rest of stuff
Custom asynchronous operations:
let group = AsyncGroup()
group.enter()
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
// Do stuff
group.leave()
}
group.enter()
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
// Do other stuff in parallel
group.leave()
}
// Wait for both to finish
group.wait()
// Do rest of stuff
License
The MIT License (MIT)
Copyright (c) 2016 Tobias Due Munk
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.
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