Simple CGD Based Debouncing / Deduping

DispatchQueue+Dedupe.swift

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//    DispatchQueue+Dedupe.swift
//    Created by James Van-As on 21/09/18.

import Foundation

extension DispatchQueue {

    /**
     - parameters:
        - target: Object used as the sentinel for de-duplication.
        - delay: The time window for de-duplication to occur
        - work: The work item to be invoked on the queue.

     Performs work only once for the given target, given the time window. The last added work closure
     is the work that will finally execute.

     Note: This is currently only safe to call from the main thread.

     Example usage:
     ```
     DispatchQueue.main.asyncDeduped(target: self, after: 1.0) { [weak self] in
         self?.doTheWork()
     }
     ```
     */
    public func asyncDeduped(target: AnyObject, after delay: TimeInterval, execute work: @escaping @convention(block) () -> Void) {
        let dedupeIdentifier = DispatchQueue.dedupeIdentifierFor(target)
        if let existingWorkItem = DispatchQueue.workItems.removeValue(forKey: dedupeIdentifier) {
            existingWorkItem.cancel()
            NSLog("Deduped work item: \(dedupeIdentifier)")
        }
        let workItem = DispatchWorkItem {
            DispatchQueue.workItems.removeValue(forKey: dedupeIdentifier)

            for ptr in DispatchQueue.weakTargets.allObjects {
                if dedupeIdentifier == DispatchQueue.dedupeIdentifierFor(ptr as AnyObject) {
                    work()
                    NSLog("Ran work item: \(dedupeIdentifier)")
                    break
                }
            }
        }

        DispatchQueue.workItems[dedupeIdentifier] = workItem
        DispatchQueue.weakTargets.addPointer(Unmanaged.passUnretained(target).toOpaque())

        asyncAfter(deadline: .now() + delay, execute: workItem)
    }

}

// MARK: - Static Properties for De-Duping

private extension DispatchQueue {

    static var workItems = [AnyHashable : DispatchWorkItem]()

    static var weakTargets = NSPointerArray.weakObjects()

    static func dedupeIdentifierFor(_ object: AnyObject) -> String {
        return "\(Unmanaged.passUnretained(object).toOpaque())." + String(describing: object)
    }

}

Thank you for sharing this, it's fantastic!

No worries. To be honest I've moved away from using CGD in my current project so haven't used it in a while. Hopefully it still works!

Important to note that this code will have a data race if this method called from a different queue that the target one or the target queue is concurrent.

thank you for sharing