為了使鎖定機制允許鎖定多個讀取器(而不是一個寫入器)訪問某個資源，可以使用 ReaderWriterLockSlim 類。這個類提供了一個鎖定功能，如果沒有寫入器鎖定資源，就允許多個讀取器訪問資源，但只能有一個寫入器鎖定該資源。

ReaderWriterLockSlim 類有阻塞或不阻塞的方法來獲取讀取鎖，如阻塞的EnterReadLock() 和不阻塞的 TryEnterReadLock() 方法，還可以使用阻塞的EnterWriteLock() 和不阻塞的 TryEnterWriteLock() 方法獲得寫入鎖定。如果任務先讀取資源,之后寫入資源,它就可以使用 EnterUpgradableReadLock() 或 TryEnterUpgradableReadLock() 方法獲得可升級的讀取鎖定。有了這個鎖定，就可以獲得寫入鎖定，而不需要釋放讀取鎖定。

這個類的幾個屬性提供了當前鎖定的相關信息。如CurrentReadCount、WaitingReadCount、WaitingUpgradableReadCount 和 WaitingWriteCount。

下面的示例程序創建了一個包含 6 項的集合和一個 ReaderWriterLockSlim() 對象。ReaderMethod() 方法獲得一個讀取鎖定，讀取列表中的所有項，并把它們寫到控制臺中。WriterMethod(0 方法試圖獲得一個寫入鎖定，以改變集合的所有值。在Main()方法中，啟動6個任務，以調用 ReaderMethod()或WriterMethod()方法。

class Program {private static List<int> _items = new List<int>() { 0，1，2，3，4，5}; private static ReaderWriterLockSlim _rwl =new ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion);public static void ReaderMethod(object reader) {try{_rwl.EnterReadLock();For (int i = 0; i < _items.Count; i++){Console.WriteLine($"reader {reader}, loop: {i}, item: {_items[i]}"); Task.Delay(40).Wait();}}finally{_rwl.ExitReadLock();}}public static void WriterMethod(object writer) {try{while (!_rwl.TryEnterWriteLock(50)){Console.WriteLine($"Writer {writer} waiting for the write lock"); Console.WriteLine($"current reader count:(_rwl.CurrentReadCount}");}Console.WriteLine($"Writer {writer) acquired the lock");for (int i = 0; i < _items.Count; i++){_items[i]++;Task.Delay(50).Wait();}Console.WriteLine($"Writer {writer} finished");}finally{_rwl.ExitWriteLock();}}static void Main() {var taskFactory = new TaskFactory(TaskCreationOptions.LongRunning,TaskContinuationOptions.None); var tasks = new Task[6];tasks[0] = taskFactory.StartNew(WriterMethod, 1); tasks[1] = taskFactory.StartNew(ReaderMethod, 1);tasks[2] = taskFactory.StartNew(ReaderMethod, 2);tasks[3] = taskFactory.StartNew(WriterMethod, 2);tasks[4] = taskFactory.StartNew(ReaderMethod, 3); tasks[5] = taskFactory.StartNew(ReaderMethod, 4); Task.WaitAll(tasks);}}

運行這個應用程序，可以看到第一個寫入器先獲得鎖定。第二個寫入器和所有的讀取器需要等待。接著，讀取器可以同時工作，而第二個寫入器仍在等待資源。?

Writer?1?acquired?the?lock Writer 2 waiting for the write lock current reader count: 0 Writer?2?waiting?for?the?write?lock? current?reader?count:?0 Writer 2 waiting for the write lock current reader count: 0 Writer?2?waiting?for?the?write?lock? current?reader?count:?0? Writer?1?finished reader?4,?loop:?0，item:?1? reader 1, loop: 0, item: 1 Writer?2?waiting?for?the?write?lock? current?reader?count:?4 reader?2,?loop:?0，item:?1? reader 3, loop: 0, item: 1 reader 4，loop: 1, item: 2 reader?1,?loop:?1,?item:?2 reader?3,?loop:?1，item:?2 reader 2, loop: 1, item: 2 Writer 2 waiting for the write lock current?reader?count:?4 reader 4, loop: 2, item: 3 reader?l,?loop:?2，item:?3 reader 2, loop: 2，item: 3 reader 3, loop: 2, item: 3 Writer 2 waiting for the write lock current reader count: 4 reader 4, loop: 3, item: 4 reader?1,?loop:?3，item:?4 reader?2,?loop:?3,?item:?4? reader?3,?loop:?3,?item:?4 reader 4, loop: 4, item: 5 reader 1, loop: 4, item: 5 Writer 2 waiting for the write lock current reader count: 4 reader 2, loop: 4, item: 5 reader 3, loop: 4, item: 5 reader?4,?loop:?5,?item:?6? reader 1，loop: 5，item: 6 reader 2, loop: 5, item: 6 reader 3, loop: 5, item: 6 Writer 2 waiting for the write lock current reader count: 4 Writer 2 acquired the lock Writer?2?finished

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