锁-读写锁-Swift

实现一 pthread_mutex_t：

ReadWriteLock/Sources/ReadWriteLock at main · SomeRandomiOSDev/ReadWriteLock · GitHub

https://swiftpackageindex.com/reers/reerkit/1.0.39/documentation/reerkit/readwritelock/

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//  THE SOFTWARE.

#if canImport(Darwin)
import Darwin

/// ReerKit: Represents a reader-writer lock. Note that this implementation is not recursive.
public final class ReadWriteLock {
    
    private var readMutex = pthread_mutex_t()
    private var writeMutex = pthread_mutex_t()
    private var readCount: UInt = 0
    
    public init() {
        pthread_mutex_init(&readMutex, nil)
        pthread_mutex_init(&writeMutex, nil)
    }
    
    deinit {
        pthread_mutex_destroy(&readMutex)
        pthread_mutex_destroy(&writeMutex)
    }
    
    public func readLock() {
        pthread_mutex_lock(&readMutex)
        defer { pthread_mutex_unlock(&readMutex) }
        if readCount == 0 {
            pthread_mutex_lock(&writeMutex)
        }
        readCount += 1
    }
    
    /// ReerKit: Returns true if the lock was succesfully locked and false if the lock was already locked.
    @discardableResult
    public func tryReadLock() -> Bool {
        pthread_mutex_lock(&readMutex)
        defer { pthread_mutex_unlock(&readMutex) }
        let success = (readCount == 0)
            ? pthread_mutex_trylock(&writeMutex) == 0
            : true
        if success {
            readCount += 1
        }
        return success
    }
    
    public func readUnlock() {
        pthread_mutex_lock(&readMutex)
        defer { pthread_mutex_unlock(&readMutex) }
        if readCount > 0 {
            readCount -= 1
            if readCount == 0 {
                pthread_mutex_unlock(&writeMutex)
            }
        }
    }
    
    public func writeLock() {
        pthread_mutex_lock(&writeMutex)
    }
    
    /// ReerKit: Returns true if the lock was succesfully locked and false if the lock was already locked.
    @discardableResult
    public func tryWriteLock() -> Bool {
        return pthread_mutex_trylock(&writeMutex) == 0
    }
    
    public func writeUnlock() {
        pthread_mutex_unlock(&writeMutex)
    }

    public func readAround<Result>(_ execute: () throws -> Result) rethrows -> Result {
        readLock()
        defer { readUnlock() }
        return try execute()
    }

    public func writeAround<Result>(_ execute: () throws -> Result) rethrows -> Result {
        writeLock()
        defer { writeUnlock() }
        return try execute()
    }
}

#endif

实现二 NSLock：

class ReadWriteLockTT {
    private let readLock = NSLock()
    private let writeLock = NSLock()
    private var readersCount = 0
    
    func read() {
        readLock.lock()
        readersCount += 1
        if readersCount == 1 {
            writeLock.lock()
        }
        readLock.unlock()
    }
    
    func readUnlock() {
        readLock.lock()
        readersCount -= 1
        if readersCount == 0 {
            writeLock.unlock()
        }
        readLock.unlock()
    }
    
    func write() {
        writeLock.lock()
    }
    
    func writeUnlock() {
        writeLock.unlock()
    }
    
    func test() {
        let rwLock = ReadWriteLockTT()

//        // 模拟多个读操作线程
//        DispatchQueue.concurrentPerform(iterations: 100) { _ in
//            rwLock.read()
//            // 这里执行读取共享资源的代码逻辑
//            print("执行读取操作")
//            rwLock.readUnlock()
//        }
//
//        // 模拟写操作线程
//        DispatchQueue.global().async {
//            rwLock.write()
//            // 这里执行写入共享资源的代码逻辑
//            print("执行写入操作")
//            rwLock.writeUnlock()
//        }
        var value = 0
        // 读线程
        DispatchQueue.global().async {
            for _ in 0..<20000 {
//                rwLock.read { value in
//                    print("Read value: \(value)")
//                }
                rwLock.read()
                // 这里执行读取共享资源的代码逻辑
                print("执行读取操作==\(value)")
                rwLock.readUnlock()
            }
        }

        // 写线程
        DispatchQueue.global().async {
            
            
            for i in 1...5 {
                sleep(1)  // 模拟写操作的延迟
//                rwLock.write(value: i)
                rwLock.write()
                // 这里执行写入共享资源的代码逻辑
                value += 1
                print("执行写入操作==\(value)")
                rwLock.writeUnlock()
                
//                print("Written value: \(i)")
            }
        }
        
        DispatchQueue.global().asyncAfter(deadline: .now() + 200.0) {
            print("打印完成")
        }
        sleep(200)

    }
}

实现三 pthread_rwlock_t ：

swift-design-patterns/Concurrency Design Patterns/ReadWriteLock/ReadWriteLock.md at main · eleev/swift-design-patterns · GitHub

import Foundation

class ReadWriteLock {
    private var rwlock = pthread_rwlock_t()

    init() {
        pthread_rwlock_init(&rwlock, nil)
    }

    deinit {
        pthread_rwlock_destroy(&rwlock)
    }

    func read<T>(_ closure: () -> T) -> T {
        pthread_rwlock_rdlock(&rwlock)
        defer { pthread_rwlock_unlock(&rwlock) }
        return closure()
    }

    func write(_ closure: () -> Void) {
        pthread_rwlock_wrlock(&rwlock)
        defer { pthread_rwlock_unlock(&rwlock) }
        closure()
    }
}

let readWriteLock = ReadWriteLock()

// Reading data with a read lock
let data = readWriteLock.read { () -> Data in
    // Read shared data here
    return sharedData
}

// Writing data with a write lock
readWriteLock.write {
    // Modify shared data here
    sharedData = newData
}

实现四 GCD 递归锁：

使用 GCD 实现属性的多读单写_gcd实现多读单写-优快云博客

    private let queue = DispatchQueue(label: "com.example.readwrite", attributes: .concurrent)
    
    // 读操作
    func read(completion: @escaping (Int) -> Void) {
        queue.sync {
            completion(self.data)
        }
    }
    
    // 写操作
    func write(value: Int) {
        queue.async(flags: .barrier) {
            self.data = value
        }
    }