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Creating Thread-Safe Arrays in Swift: http://basememara.com/creating-thread-safe-arrays-in-swift/
import Foundation
import PlaygroundSupport
/// A thread-safe array.
public class SynchronizedArray<Element> {
private let queue = DispatchQueue(label: "io.zamzam.ZamzamKit.SynchronizedArray", attributes: .concurrent)
private var array = [Element]()
public init() { }
public convenience init(_ array: [Element]) {
self.init()
self.array = array
}
}
// MARK: - Properties
public extension SynchronizedArray {
/// The first element of the collection.
var first: Element? {
var result: Element?
queue.sync { result = self.array.first }
return result
}
/// The last element of the collection.
var last: Element? {
var result: Element?
queue.sync { result = self.array.last }
return result
}
/// The number of elements in the array.
var count: Int {
var result = 0
queue.sync { result = self.array.count }
return result
}
/// A Boolean value indicating whether the collection is empty.
var isEmpty: Bool {
var result = false
queue.sync { result = self.array.isEmpty }
return result
}
/// A textual representation of the array and its elements.
var description: String {
var result = ""
queue.sync { result = self.array.description }
return result
}
}
// MARK: - Immutable
public extension SynchronizedArray {
/// Returns the first element of the sequence that satisfies the given predicate.
///
/// - Parameter predicate: A closure that takes an element of the sequence as its argument and returns a Boolean value indicating whether the element is a match.
/// - Returns: The first element of the sequence that satisfies predicate, or nil if there is no element that satisfies predicate.
func first(where predicate: (Element) -> Bool) -> Element? {
var result: Element?
queue.sync { result = self.array.first(where: predicate) }
return result
}
/// Returns the last element of the sequence that satisfies the given predicate.
///
/// - Parameter predicate: A closure that takes an element of the sequence as its argument and returns a Boolean value indicating whether the element is a match.
/// - Returns: The last element of the sequence that satisfies predicate, or nil if there is no element that satisfies predicate.
func last(where predicate: (Element) -> Bool) -> Element? {
var result: Element?
queue.sync { result = self.array.last(where: predicate) }
return result
}
/// Returns an array containing, in order, the elements of the sequence that satisfy the given predicate.
///
/// - Parameter isIncluded: A closure that takes an element of the sequence as its argument and returns a Boolean value indicating whether the element should be included in the returned array.
/// - Returns: An array of the elements that includeElement allowed.
func filter(_ isIncluded: @escaping (Element) -> Bool) -> SynchronizedArray {
var result: SynchronizedArray?
queue.sync { result = SynchronizedArray(self.array.filter(isIncluded)) }
return result!
}
/// Returns the first index in which an element of the collection satisfies the given predicate.
///
/// - Parameter predicate: A closure that takes an element as its argument and returns a Boolean value that indicates whether the passed element represents a match.
/// - Returns: The index of the first element for which predicate returns true. If no elements in the collection satisfy the given predicate, returns nil.
func index(where predicate: (Element) -> Bool) -> Int? {
var result: Int?
queue.sync { result = self.array.index(where: predicate) }
return result
}
/// Returns the elements of the collection, sorted using the given predicate as the comparison between elements.
///
/// - Parameter areInIncreasingOrder: A predicate that returns true if its first argument should be ordered before its second argument; otherwise, false.
/// - Returns: A sorted array of the collection’s elements.
func sorted(by areInIncreasingOrder: (Element, Element) -> Bool) -> SynchronizedArray {
var result: SynchronizedArray?
queue.sync { result = SynchronizedArray(self.array.sorted(by: areInIncreasingOrder)) }
return result!
}
/// Returns an array containing the results of mapping the given closure over the sequence’s elements.
///
/// - Parameter transform: A closure that accepts an element of this sequence as its argument and returns an optional value.
/// - Returns: An array of the non-nil results of calling transform with each element of the sequence.
func map<ElementOfResult>(_ transform: @escaping (Element) -> ElementOfResult) -> [ElementOfResult] {
var result = [ElementOfResult]()
queue.sync { result = self.array.map(transform) }
return result
}
/// Returns an array containing the non-nil results of calling the given transformation with each element of this sequence.
///
/// - Parameter transform: A closure that accepts an element of this sequence as its argument and returns an optional value.
/// - Returns: An array of the non-nil results of calling transform with each element of the sequence.
func compactMap<ElementOfResult>(_ transform: (Element) -> ElementOfResult?) -> [ElementOfResult] {
var result = [ElementOfResult]()
queue.sync { result = self.array.compactMap(transform) }
return result
}
/// Returns the result of combining the elements of the sequence using the given closure.
///
/// - Parameters:
/// - initialResult: The value to use as the initial accumulating value. initialResult is passed to nextPartialResult the first time the closure is executed.
/// - nextPartialResult: A closure that combines an accumulating value and an element of the sequence into a new accumulating value, to be used in the next call of the nextPartialResult closure or returned to the caller.
/// - Returns: The final accumulated value. If the sequence has no elements, the result is initialResult.
func reduce<ElementOfResult>(_ initialResult: ElementOfResult, _ nextPartialResult: @escaping (ElementOfResult, Element) -> ElementOfResult) -> ElementOfResult {
var result: ElementOfResult?
queue.sync { result = self.array.reduce(initialResult, nextPartialResult) }
return result ?? initialResult
}
/// Returns the result of combining the elements of the sequence using the given closure.
///
/// - Parameters:
/// - initialResult: The value to use as the initial accumulating value.
/// - updateAccumulatingResult: A closure that updates the accumulating value with an element of the sequence.
/// - Returns: The final accumulated value. If the sequence has no elements, the result is initialResult.
func reduce<ElementOfResult>(into initialResult: ElementOfResult, _ updateAccumulatingResult: @escaping (inout ElementOfResult, Element) -> ()) -> ElementOfResult {
var result: ElementOfResult?
queue.sync { result = self.array.reduce(into: initialResult, updateAccumulatingResult) }
return result ?? initialResult
}
/// Calls the given closure on each element in the sequence in the same order as a for-in loop.
///
/// - Parameter body: A closure that takes an element of the sequence as a parameter.
func forEach(_ body: (Element) -> Void) {
queue.sync { self.array.forEach(body) }
}
/// Returns a Boolean value indicating whether the sequence contains an element that satisfies the given predicate.
///
/// - Parameter predicate: A closure that takes an element of the sequence as its argument and returns a Boolean value that indicates whether the passed element represents a match.
/// - Returns: true if the sequence contains an element that satisfies predicate; otherwise, false.
func contains(where predicate: (Element) -> Bool) -> Bool {
var result = false
queue.sync { result = self.array.contains(where: predicate) }
return result
}
/// Returns a Boolean value indicating whether every element of a sequence satisfies a given predicate.
///
/// - Parameter predicate: A closure that takes an element of the sequence as its argument and returns a Boolean value that indicates whether the passed element satisfies a condition.
/// - Returns: true if the sequence contains only elements that satisfy predicate; otherwise, false.
func allSatisfy(_ predicate: (Element) -> Bool) -> Bool {
var result = false
queue.sync { result = self.array.allSatisfy(predicate) }
return result
}
}
// MARK: - Mutable
public extension SynchronizedArray {
/// Adds a new element at the end of the array.
///
/// - Parameter element: The element to append to the array.
func append(_ element: Element) {
queue.async(flags: .barrier) {
self.array.append(element)
}
}
/// Adds new elements at the end of the array.
///
/// - Parameter element: The elements to append to the array.
func append(_ elements: [Element]) {
queue.async(flags: .barrier) {
self.array += elements
}
}
/// Inserts a new element at the specified position.
///
/// - Parameters:
/// - element: The new element to insert into the array.
/// - index: The position at which to insert the new element.
func insert(_ element: Element, at index: Int) {
queue.async(flags: .barrier) {
self.array.insert(element, at: index)
}
}
/// Removes and returns the element at the specified position.
///
/// - Parameters:
/// - index: The position of the element to remove.
/// - completion: The handler with the removed element.
func remove(at index: Int, completion: ((Element) -> Void)? = nil) {
queue.async(flags: .barrier) {
let element = self.array.remove(at: index)
DispatchQueue.main.async { completion?(element) }
}
}
/// Removes and returns the elements that meet the criteria.
///
/// - Parameters:
/// - predicate: A closure that takes an element of the sequence as its argument and returns a Boolean value indicating whether the element is a match.
/// - completion: The handler with the removed elements.
func remove(where predicate: @escaping (Element) -> Bool, completion: (([Element]) -> Void)? = nil) {
queue.async(flags: .barrier) {
var elements = [Element]()
while let index = self.array.index(where: predicate) {
elements.append(self.array.remove(at: index))
}
DispatchQueue.main.async { completion?(elements) }
}
}
/// Removes all elements from the array.
///
/// - Parameter completion: The handler with the removed elements.
func removeAll(completion: (([Element]) -> Void)? = nil) {
queue.async(flags: .barrier) {
let elements = self.array
self.array.removeAll()
DispatchQueue.main.async { completion?(elements) }
}
}
}
public extension SynchronizedArray {
/// Accesses the element at the specified position if it exists.
///
/// - Parameter index: The position of the element to access.
/// - Returns: optional element if it exists.
subscript(index: Int) -> Element? {
get {
var result: Element?
queue.sync {
guard self.array.startIndex..<self.array.endIndex ~= index else { return }
result = self.array[index]
}
return result
}
set {
guard let newValue = newValue else { return }
queue.async(flags: .barrier) {
self.array[index] = newValue
}
}
}
}
// MARK: - Equatable
public extension SynchronizedArray where Element: Equatable {
/// Returns a Boolean value indicating whether the sequence contains the given element.
///
/// - Parameter element: The element to find in the sequence.
/// - Returns: true if the element was found in the sequence; otherwise, false.
func contains(_ element: Element) -> Bool {
var result = false
queue.sync { result = self.array.contains(element) }
return result
}
}
// MARK: - Infix operators
public extension SynchronizedArray {
/// Adds a new element at the end of the array.
///
/// - Parameters:
/// - left: The collection to append to.
/// - right: The element to append to the array.
static func +=(left: inout SynchronizedArray, right: Element) {
left.append(right)
}
/// Adds new elements at the end of the array.
///
/// - Parameters:
/// - left: The collection to append to.
/// - right: The elements to append to the array.
static func +=(left: inout SynchronizedArray, right: [Element]) {
left.append(right)
}
}
// Thread-safe array
do {
var array = SynchronizedArray<Int>()
var iterations = 1000
let start = Date().timeIntervalSince1970
DispatchQueue.concurrentPerform(iterations: iterations) { index in
let last = array.last ?? 0
array.append(last + 1)
DispatchQueue.global().sync {
iterations -= 1
// Final loop
guard iterations <= 0 else { return }
let message = String(format: "Safe loop took %.3f seconds, count: %d.",
Date().timeIntervalSince1970 - start,
array.count)
print(message)
}
}
}
PlaygroundPage.current.needsIndefiniteExecution = true
@doctorcolinsmith

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commented Dec 14, 2017

This is a really nice bit of code. Any chance of turning this into a framework with a non-viral open source license so I can use it in my app?

Cocoapods support would be a nice bonus ;-)

@karthikAdaptavant

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commented Jul 31, 2018

i have tried with Xcode 9.4.1 TSan. Still i am getting race condition
screen shot 2018-07-31 at 2 21 15 pm

@neoneye

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commented Oct 3, 2018

In Xcode10 there is a warning about flatMaphas been renamed to compactMap.

@basememara

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Owner Author

commented Dec 5, 2018

I updated to Swift 4.2 and expose some more array functions like reduce and allSatisfy.

From now, this code will be rolled-in and maintained within another library:
https://github.com/ZamzamInc/ZamzamKit/blob/master/Sources/Models/SynchronizedArray.swift

Thanks for all the feedback and comments.

@samishchandra

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commented Feb 7, 2019

Why [weak self] is not used while submitting tasks to the queue ?

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