Grand Central Dispatch for concurrency

import Foundation
import UIKit

class ImageProcessor {
    // Background processing with main thread updates
    func processImage(_ image: UIImage, completion: @escaping (UIImage?) -> Void) {
        DispatchQueue.global(qos: .userInitiated).async {
            // Heavy processing on background thread
            let processedImage = self.applyFilters(to: image)

            // Return to main thread for UI updates
            DispatchQueue.main.async {
                completion(processedImage)
            }
        }
    }

    private func applyFilters(to image: UIImage) -> UIImage? {
        // Simulate heavy processing
        Thread.sleep(forTimeInterval: 2)
        return image
    }
}

// Dispatch groups for coordinating multiple tasks
class DataSynchronizer {
    func syncAllData(completion: @escaping (Bool) -> Void) {
        let group = DispatchGroup()
        var hasError = false

        group.enter()
        fetchPosts { success in
            if !success { hasError = true }
            group.leave()
        }

        group.enter()
        fetchComments { success in
            if !success { hasError = true }
            group.leave()
        }

        group.enter()
        fetchUsers { success in
            if !success { hasError = true }
            group.leave()
        }

        group.notify(queue: .main) {
            completion(!hasError)
        }
    }

    private func fetchPosts(completion: @escaping (Bool) -> Void) {
        DispatchQueue.global().async {
            Thread.sleep(forTimeInterval: 1)
            completion(true)
        }
    }

    private func fetchComments(completion: @escaping (Bool) -> Void) {
        DispatchQueue.global().async {
            Thread.sleep(forTimeInterval: 1)
            completion(true)
        }
    }

    private func fetchUsers(completion: @escaping (Bool) -> Void) {
        DispatchQueue.global().async {
            Thread.sleep(forTimeInterval: 1)
            completion(true)
        }
    }
}

// Custom serial queue for thread-safe access
class ThreadSafeCache<Key: Hashable, Value> {
    private var cache: [Key: Value] = [:]
    private let queue = DispatchQueue(label: "com.myapp.cache", attributes: .concurrent)

    func get(_ key: Key) -> Value? {
        queue.sync {
            cache[key]
        }
    }

    func set(_ value: Value, forKey key: Key) {
        queue.async(flags: .barrier) {
            self.cache[key] = value
        }
    }

    func remove(_ key: Key) {
        queue.async(flags: .barrier) {
            self.cache.removeValue(forKey: key)
        }
    }
}

// Debouncing with dispatch work items
class SearchDebouncer {
    private var workItem: DispatchWorkItem?
    private let delay: TimeInterval

    init(delay: TimeInterval = 0.3) {
        self.delay = delay
    }

    func debounce(action: @escaping () -> Void) {
        workItem?.cancel()

        let newWorkItem = DispatchWorkItem(block: action)
        workItem = newWorkItem

        DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: newWorkItem)
    }
}