Latest 0.8.2
License MIT
Platforms ios 8.0, osx 10.9, requires ARC
Frameworks Foundation


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A Swift-er way to do GCD-related things.



pod 'Do' # Latest Swift compatible

pod 'Do/2.0' # Swift 2.0 compatible

pod 'Do/1.2' # Swift 1.2 compatible


Drag Do-[Swift version].swift into your project.



  • Queues (access to global queues, and current queue checking)
  • Sync (deadlock safe dispatch_sync/dispatch_barrier_sync with return values)
  • Loop (deadlock safe dispatch_apply with range version)
  • After (cancellable dispatch_after)
  • Concurrent (simple mechanism for async operations with a limit to how many can process concurrently)
  • Once (hackery-enabled succinct dispatch_once)
  • Throttle (hackery-enabled succinct throttling)
  • Async (convenience functions related to dispatch_async)


Do! provides easy access to the main queue, global priority queues, as well as the global ‘quality of service’ queues available in OS X 10.10 and iOS 8.0 and later (with appropriate fallbacks in place).

Do.mainQueue // The "main" dispatch queue.

Do.highPriorityQueue // The global "high priority" dispatch queue.

Do.defaultQueue // The global "default" dispatch queue.

Do.lowPriorityQueue // The global "low priority" dispatch queue.

Do.backgroundQueue // The global "background" dispatch queue.

Do.userInteractiveQueue // The global "user interactive" (super high priority?) dispatch queue.

Do.userInitiatedQueue // The global "user initiated" (equivalent to "high priority") dispatch queue.

Do.utilityQueue // The global "utility" (equivalent to "low priority") dispatch queue.

Do! also provides a way to check whether you are currently dispatched on a specific queue by comparing labels (give your queues labels!).

if Do.isCurrentQueue(mainQueue) {
    print("Hello from the main queue!")


Do! provides a wrapper around dispatch_sync and dispatch_barrier_sync that is succinct and deadlock safe (well, more deadlock safe – it uses Do.isCurrentQueue to avoid this, but that only helps if you try to dispatch to the current queue, not one higher up in the dispatch tree).

Do.sync(someSerialQueue) {
    print("Hello world!")
Do.barrierSync(someConcurrentQueue) {
    print("Hello world!")

More importantly, Do! provides versions which returns values, which is perfect for synchronizing access to resources…

let resource: Resource = Do.sync(someSerialQueue) {
    // .. heavy work that should happen serially...

    return importantResource
let resource: Resource = Do.barrierSync(someConcurrentQueue) {
    // .. heavy work that should block queue...

    return importantResource

.. or even synchronizing properties.

class Variable {
    private var _value: Any

    var value: Any {
        get { return barrierSync(someConcurrentQueue) { self._value } }
        set { barrierSync(someConcurrentQueue) { self._value = newValue } }


Do! provides a wrapper around dispatch_apply that is succinct and deadlock safe (again, more deadlock safe). If the targetted queue is the current dispatch queue (or nil), it reverts to a plain loop.

Do.loop(100, highPriorityQueue) { i in
Do.loop(10) { i in

Do! also provides a version which takes a range instead of an iterations count.

Do.loop(15..<55, highPriorityQueue) { i in


Do! provides a wrapper around dispatch_after that is succinct and defaults to the main queue…

Do.after(3.0) {
    print("Hello world!")
Do.after(0.5, backgroundQueue) {
    print("Hello world!")

.. as well as a version returning a block for cancellation of the scheduled dispatch.

let cancel = Do.afterCancel(10) {
    print("Hello world!")

Do.after(2) {


Do! provides a simple but powerful mechanism for dispatching async operations (which might have async/nested dispatches themselves) that can be limited to processing sequentially or N at a time.

static token = Do.ConcurrentToken() // store this somewhere!

// ...

for i in 0..<100 {
    Do.concurrent(token, highPriorityQueue) { done in
        // some heavy stuff...


// the 100 operations will process one at a time...
static token = Do.ConcurrentToken(limit: 5)

for i in 0..<50 {
    Do.concurrent(token, mainQueue) { done in
        Do.after(0.5) {

    Do.concurrent(token, backgroundQueue) { done in
        Do.after(1.0) {

// the 100 operations (with different logic/queues) will process 5 at a time


Do! provides an uber-succinct wrapper around dispatch_once (using hackery.. so beware, it works/is stable, but is not guaranteed to be the most performant solution).

Do.once {
    print("Hello world!")

Do! also provides a version which stores the result of the initial dispatch, and simply returns the value on all subsequent dispatches (again, hackery).

for i in 0..<10 {
    let message: String = Do.once {
        print("Some lazy/heavy stuff that should only happen once ;)")

        return "Hello world!"



Do! provides an uber-succinct way to dispatch a block a max of once per N seconds (again, hackery).

Do.throttle(3.4) {
    print("Hello world!")
Do.throttle(0.5, backgroundQueue) {
    print("Hello world!")


Do! provides a wrapper around dispatch_async that is succinct, and convenient. That’s it really, though. For added features (e.g. chaining) I recommend Async by duemunk.

Do.async(userInitiatedQueue) { ... }
Do.barrierAsync(userInitiatedQueue) { ... }
let group = dispatch_group_create()

Do.groupAsync(group, userInitiatedQueue) { ... }

Do.barrierGroupAsync(group, userInitiatedQueue) { ... }
Do.main { ... }

Do.background { ... }

Do.userInteractive { ... }

Do.userInitiated { ... }

Latest podspec

    "name": "Do",
    "version": "0.8.2",
    "summary": "A Swift-er way to do GCD-related things.",
    "license": {
        "type": "MIT",
        "file": "LICENSE"
    "authors": {
        "Mathew Huusko V": "[email protected]"
    "social_media_url": "",
    "homepage": "",
    "source": {
        "git": "",
        "tag": "0.8.2"
    "requires_arc": true,
    "frameworks": "Foundation",
    "platforms": {
        "ios": "8.0",
        "osx": "10.9"
    "default_subspecs": "2.0",
    "subspecs": [
            "name": "1.2",
            "source_files": "Do-1.2.swift"
            "name": "2.0",
            "source_files": "Do-2.0.swift"

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