FinalOperationSynchronizer.swift

import Foundation

@objc class FinalOperationSynchronizer: NSObject {
    @objc private(set) var operations: [Operation]
    @objc private(set) var finalOperation: Operation
    @objc private(set) var cancelOperation: Operation?
    
    private(set) var queue: OperationQueue?
    
    @objc init(with operations: [Operation], and finalOperation: Operation, with cancelOperation: Operation) {
        operations.forEach { (operation) in
            finalOperation.addDependency(operation)
        }
        self.operations = operations
        self.finalOperation = finalOperation
        self.cancelOperation = cancelOperation
        super.init()
    }
    
    @objc func prepareQueue() {
        queue = OperationQueue()
        queue?.qualityOfService = .default
    }
    
    @objc func executeFinalOperationWhenOperationsReady() {
        if queue == nil {
            prepareQueue()
        }
        
        queue!.addOperation(finalOperation)
    }
    
    @objc func cancelAllOperations() {
        queue?.cancelAllOperations()
    }
    
    @objc func cancelAllOperationsAndExecuteCancelOperation() {
        queue?.cancelAllOperations()
        if let cancelOperation = self.cancelOperation {
            queue?.addOperation(cancelOperation)
        }

    }
}

Executes a FinalOperation when all other operation have been executed. Also fully compatible with Objective-C. Since I took it from an Objective-C project.