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//
// MainThreadOperationQueue.swift
// RSCore
//
// Created by Brent Simmons on 1/10/20.
// Copyright © 2020 Ranchero Software, LLC. All rights reserved.
//
import Foundation
public protocol MainThreadOperationDelegate: class {
func operationDidComplete(_ operation: MainThreadOperation)
func cancelOperation(_ operation: MainThreadOperation)
func make(_ childOperation: MainThreadOperation, dependOn parentOperation: MainThreadOperation)
}
/// Manage a queue of MainThreadOperation tasks.
/// Runs them one at a time; runs them on the main thread.
/// Any operation can use DispatchQueue or whatever to run code off of the main thread.
/// An operation calls back to the queue when it’s completed or canceled.
/// Use this only on the main thread.
/// The operation can be suspended and resumed.
/// It is *not* suspended on creation.
public final class MainThreadOperationQueue {
/// Use the shared queue when you don’t need to create a separate queue.
public static let shared: MainThreadOperationQueue = {
MainThreadOperationQueue()
}()
private var operations = [Int: MainThreadOperation]()
private var pendingOperationIDs = [Int]()
private var currentOperationID: Int?
private static var incrementingID = 0
private var isSuspended = false
private let dependencies = MainThreadOperationDependencies()
/// Meant for testing; not intended to be useful.
public var pendingOperationsCount: Int {
return pendingOperationIDs.count
}
public init() {
// Silence compiler complaint about init not being public.
}
deinit {
cancelAllOperations()
}
/// Add an operation to the queue.
public func add(_ operation: MainThreadOperation) {
precondition(Thread.isMainThread)
operation.operationDelegate = self
let operationID = ensureOperationID(operation)
operations[operationID] = operation
assert(!pendingOperationIDs.contains(operationID))
if !pendingOperationIDs.contains(operationID) {
pendingOperationIDs.append(operationID)
}
runNextOperationIfNeeded()
}
/// Add multiple operations to the queue.
/// This has the same effect as calling addOperation one-by-one.
public func addOperations(_ operations: [MainThreadOperation]) {
operations.forEach{ add($0) }
}
/// Add a dependency. Do this *before* calling addOperation, since addOperation might run the operation right away.
public func make(_ childOperation: MainThreadOperation, dependOn parentOperation: MainThreadOperation) {
precondition(Thread.isMainThread)
let childOperationID = ensureOperationID(childOperation)
let parentOperationID = ensureOperationID(parentOperation)
dependencies.make(childOperationID, dependOn: parentOperationID)
}
/// Cancel all the current and pending operations.
public func cancelAllOperations() {
precondition(Thread.isMainThread)
var operationIDsToCancel = pendingOperationIDs
if let currentOperationID = currentOperationID {
operationIDsToCancel.append(currentOperationID)
}
cancel(operationIDsToCancel)
}
/// Cancel some operations. If any of them have dependent operations,
/// those operations will be canceled also.
public func cancelOperations(_ operations: [MainThreadOperation]) {
precondition(Thread.isMainThread)
let operationIDsToCancel = operations.map{ ensureOperationID($0) }
assert(allOperationIDsArePendingOrCurrent(operationIDsToCancel))
assert(allOperationIDsAreInStorage(operationIDsToCancel))
cancel(operationIDsToCancel)
runNextOperationIfNeeded()
}
/// Cancel operations with the given name. If any of them have dependent
/// operations, they will be canceled too.
///
/// This will cancel the current operation, not just pending operations,
/// if it has the specified name.
public func cancelOperations(named name: String) {
precondition(Thread.isMainThread)
guard let operationsToCancel = pendingAndCurrentOperations(named: name) else {
return
}
cancelOperations(operationsToCancel)
}
/// Stop running operations until resume() is called.
/// The current operation, if there is one, will run to completion —
/// it will not be canceled.
public func suspend() {
precondition(Thread.isMainThread)
isSuspended = true
}
/// Resume running operations.
public func resume() {
precondition(Thread.isMainThread)
isSuspended = false
runNextOperationIfNeeded()
}
}
extension MainThreadOperationQueue: MainThreadOperationDelegate {
public func operationDidComplete(_ operation: MainThreadOperation) {
precondition(Thread.isMainThread)
operationDidFinish(operation)
}
public func cancelOperation(_ operation: MainThreadOperation) {
cancelOperations([operation])
}
}
private extension MainThreadOperationQueue {
var pendingOperations: [MainThreadOperation] {
return pendingOperationIDs.compactMap { (operationID) -> MainThreadOperation? in
guard let operation = operations[operationID] else {
assertionFailure("Expected operation, got nil.")
return nil
}
return operation
}
}
var currentOperation: MainThreadOperation? {
guard let operationID = currentOperationID else {
return nil
}
return operations[operationID]
}
func pendingAndCurrentOperations(named name: String) -> [MainThreadOperation]? {
var operations = pendingOperations.filter { $0.name == name }
if let current = currentOperation, current.name == name {
operations.append(current)
}
return operations.isEmpty ? nil : operations
}
func operationDidFinish(_ operation: MainThreadOperation) {
guard let operationID = operation.id else {
assertionFailure("Expected operation.id, got nil")
return
}
if let currentOperationID = currentOperationID, currentOperationID == operationID {
self.currentOperationID = nil
}
if operation.isCanceled {
dependencies.operationIDWasCanceled(operationID)
}
else {
dependencies.operationIDDidComplete(operationID)
}
callCompletionBlock(for: operation)
removeFromStorage(operation)
operation.operationDelegate = nil
runNextOperationIfNeeded()
}
func runNextOperationIfNeeded() {
DispatchQueue.main.async {
guard !self.isSuspended && !self.isRunningAnOperation() else {
return
}
guard let operation = self.popNextAvailableOperation() else {
return
}
self.currentOperationID = operation.id!
operation.run()
}
}
func isRunningAnOperation() -> Bool {
return currentOperationID != nil
}
func popNextAvailableOperation() -> MainThreadOperation? {
for operationID in pendingOperationIDs {
guard let operation = operations[operationID] else {
assertionFailure("Expected pending operation to be found in operations dictionary.")
continue
}
if operationIsAvailable(operation) {
removeOperationIDsFromPendingOperationIDs([operationID])
dependencies.operationIDWillRun(operationID)
return operation
}
}
return nil
}
func operationIsAvailable(_ operation: MainThreadOperation) -> Bool {
return !operation.isCanceled && !dependencies.operationIDIsBlockedByDependency(operation.id!)
}
func createOperationID() -> Int {
precondition(Thread.isMainThread)
Self.incrementingID += 1
return Self.incrementingID
}
func ensureOperationID(_ operation: MainThreadOperation) -> Int {
if let operationID = operation.id {
return operationID
}
let operationID = createOperationID()
operation.id = operationID
return operationID
}
func cancel(_ operationIDs: [Int]) {
guard !operationIDs.isEmpty else {
return
}
let operationIDsToCancel = operationIDsByAddingChildOperationIDs(operationIDs)
setCanceledAndRemoveDelegate(for: operationIDsToCancel)
callCompletionBlockForOperationIDs(operationIDsToCancel)
clearCurrentOperationIDIfContained(by: operationIDsToCancel)
removeOperationIDsFromPendingOperationIDs(operationIDsToCancel)
removeOperationIDsFromStorage(operationIDsToCancel)
dependencies.cancel(operationIDsToCancel)
}
func operationIDsByAddingChildOperationIDs(_ operationIDs: [Int]) -> [Int] {
var operationIDsToCancel = operationIDs
for operationID in operationIDs {
if let childOperationIDs = dependencies.childOperationIDs(for: operationID) {
operationIDsToCancel += childOperationIDs
}
}
return operationIDsToCancel
}
func setCanceledAndRemoveDelegate(for operationIDs: [Int]) {
for operationID in operationIDs {
if let operation = operations[operationID] {
operation.isCanceled = true
operation.operationDelegate = nil
}
}
}
func clearCurrentOperationIDIfContained(by operationIDs: [Int]) {
if let currentOperationID = currentOperationID, operationIDs.contains(currentOperationID) {
self.currentOperationID = nil
}
}
func removeOperationIDsFromPendingOperationIDs(_ operationIDs: [Int]) {
var updatedPendingOperationIDs = pendingOperationIDs
for operationID in operationIDs {
if let ix = updatedPendingOperationIDs.firstIndex(of: operationID) {
updatedPendingOperationIDs.remove(at: ix)
}
}
pendingOperationIDs = updatedPendingOperationIDs
}
func removeFromStorage(_ operation: MainThreadOperation) {
guard let operationID = operation.id else {
assertionFailure("Expected operation.id, got nil.")
return
}
removeOperationIDsFromStorage([operationID])
}
func removeOperationIDsFromStorage(_ operationIDs: [Int]) {
DispatchQueue.main.async {
for operationID in operationIDs {
self.operations[operationID] = nil
}
}
}
func callCompletionBlockForOperationIDs(_ operationIDs: [Int]) {
let completedOperations = operationIDs.compactMap { operations[$0] }
callCompletionBlockForOperations(completedOperations)
}
func callCompletionBlockForOperations(_ operations: [MainThreadOperation]) {
for operation in operations {
callCompletionBlock(for: operation)
}
}
func callCompletionBlock(for operation: MainThreadOperation) {
guard let completionBlock = operation.completionBlock else {
return
}
completionBlock(operation)
operation.completionBlock = nil
}
func allOperationIDsArePendingOrCurrent(_ operationIDs: [Int]) -> Bool {
// Used by an assert.
for operationID in operationIDs {
if currentOperationID != operationID && !pendingOperationIDs.contains(operationID) {
return false
}
}
return true
}
func allOperationIDsAreInStorage(_ operationIDs: [Int]) -> Bool {
// Used by an assert.
for operationID in operationIDs {
guard let _ = operations[operationID] else {
return false
}
}
return true
}
}
private final class MainThreadOperationDependencies {
private var dependencies = [Int: Dependency]() // Key is parentOperationID
private final class Dependency {
let operationID: Int
var parentOperationDidComplete = false
var isEmpty: Bool {
return childOperationIDs.isEmpty
}
var childOperationIDs = [Int]()
init(operationID: Int) {
self.operationID = operationID
}
func remove(_ childOperationID: Int) {
if let ix = childOperationIDs.firstIndex(of: childOperationID) {
childOperationIDs.remove(at: ix)
}
}
func add(_ childOperationID: Int) {
guard !childOperationIDs.contains(childOperationID) else {
return
}
childOperationIDs.append(childOperationID)
}
func operationIDIsBlocked(_ operationID: Int) -> Bool {
if parentOperationDidComplete {
return false
}
return childOperationIDs.contains(operationID)
}
}
/// Add a dependency: make childOperationID dependent on parentOperationID.
func make(_ childOperationID: Int, dependOn parentOperationID: Int) {
let dependency = ensureDependency(parentOperationID)
dependency.add(childOperationID)
}
/// Child operationIDs for a possible dependency.
func childOperationIDs(for parentOperationID: Int) -> [Int]? {
if let dependency = dependencies[parentOperationID] {
return dependency.childOperationIDs
}
return nil
}
/// Update dependencies when an operation is completed.
func operationIDDidComplete(_ operationID: Int) {
if let dependency = dependencies[operationID] {
dependency.parentOperationDidComplete = true
}
removeChildOperationID(operationID)
removeEmptyDependencies()
}
/// Update dependencies when an operation finished but was canceled.
func operationIDWasCanceled(_ operationID: Int) {
removeAllReferencesToOperationIDs([operationID])
}
/// Update dependencies when canceling operations.
func cancel(_ operationIDs: [Int]) {
removeAllReferencesToOperationIDs(operationIDs)
}
/// Update dependencies when an operation is about to run.
func operationIDWillRun(_ operationID: Int) {
removeChildOperationIDs([operationID])
}
/// Find out if an operationID is blocked by a dependency.
func operationIDIsBlockedByDependency(_ operationID: Int) -> Bool {
for dependency in dependencies.values {
if dependency.operationIDIsBlocked(operationID) {
return true
}
}
return false
}
private func ensureDependency(_ parentOperationID: Int) -> Dependency {
if let dependency = dependencies[parentOperationID] {
return dependency
}
let dependency = Dependency(operationID: parentOperationID)
dependencies[parentOperationID] = dependency
return dependency
}
}
private extension MainThreadOperationDependencies {
func removeAllReferencesToOperationIDs(_ operationIDs: [Int]) {
removeDependencies(operationIDs)
removeChildOperationIDs(operationIDs)
}
func removeDependencies(_ parentOperationIDs: [Int]) {
parentOperationIDs.forEach { dependencies[$0] = nil }
}
func removeChildOperationIDs(_ operationIDs: [Int]) {
operationIDs.forEach{ removeChildOperationID($0) }
removeEmptyDependencies()
}
func removeChildOperationID(_ operationID: Int) {
dependencies.values.forEach{ $0.remove(operationID) }
}
func removeEmptyDependencies() {
let parentOperationIDs = dependencies.keys
for parentOperationID in parentOperationIDs {
let dependency = dependencies[parentOperationID]!
if dependency.isEmpty {
dependencies[parentOperationID] = nil
}
}
}
}
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