线程安全 二

using System;
using System.Threading;

abstract class Counter
{
    protected int count = 0;

    public abstract int Read(int threadNum);
    public abstract void Increment(int threadNum); 
}

// Note that the instance variable count is shared between the two methods Read
// and Increment. Threads concurrently executing one or both of these methods can
// interfere with each other unless action is taken to synchronize access

class CounterUnsafe : Counter
{
    public override int Read(int threadNum) 
    {
        // following code is not thread-safe and has a race condition
        try 
        {
            Console.WriteLine(
                "Start Resource reading (Thread={0})count: {1}", threadNum, count);
            Thread.Sleep(250);
            Console.WriteLine(
                "Stop  Resource reading (Thread={0}) count: {1}", threadNum, count);
            return count;
        }
        finally 
        {
        }
    }

    public override void Increment(int threadNum) 
    {
        // following code is not thread-safe and has a race condition
        try 
        {
            Console.WriteLine(
                "Start Resource writing (Thread={0}) count: {1}", threadNum, count);
            // the following four lines simulate count++ with a very large
            // window of time between count being read and being incremented.
            // This large window ensures that the race condition will create
            // errors often when the code is accessed concurrently by multiple threads.
            int tempCount = count;
            Thread.Sleep(1000);
            tempCount++;
            count = tempCount;
            Console.WriteLine(
                "Stop  Resource writing (Thread={0}) count: {1}", threadNum, count);
        }
        finally 
        {
        }
    }
}

class CounterUsingInterlocked : Counter
{
    public override int Read(int threadNum) 
    {
        try 
        {
            // following is thread safe but since Increments can occur during
            //  this method, the value of count can change between the start 
            //  of the method and its return/end, if this is a problem
            //  you need to use manual locks or a synchronized context.
            Console.WriteLine(
                "Start Resource reading (Thread={0})count: {1}", threadNum, count);
            Thread.Sleep(250);
            Console.WriteLine(
                "Stop  Resource reading (Thread={0}) count: {1}", threadNum, count);
            return count;
        }
        finally 
        {
        }
    }

    public override void Increment(int threadNum) 
    {
        // ...
        // method code that doesn't require exclusive access 
        try 
        {
            Console.WriteLine(
                "Start Resource writing (Thread={0}) count: {1}", threadNum, count);
            // Note that count++ is not  an atomic operation and therefore not thread-safe.
            //  With count++ there would be a window of time between reading the value count and 
            //  incrementing the value of count during which time another thread could execute and
            //  also read and/or change the value of count. Even thought this window
            //  is much smaller than with the CounterUnsafe methods this non atomic operation
            //  still results in a race condition where an increment can be lost.
            // To make the increment of count thread-safe we use an atomic Interlocked.Increment call.
            int tempCount = Interlocked.Increment(ref count);
            Console.WriteLine(
                "Stop Resource writing (Thread={0}) count: {1}", threadNum, tempCount);
        }
        finally 
        {
        }
    }
}

class CounterUsingLock : Counter
{
    public override int Read(int threadNum) 
    {
        // ...
        // method code that doesn't require exclusive access 
        lock(this)
        {
            Console.WriteLine(
                "Start Resource reading (Thread={0})count: {1}", threadNum, count);
            Thread.Sleep(250);
            Console.WriteLine(
                "Stop Resource reading (Thread={0}) count: {1}", threadNum, count);
            return count;
        }
    }

    public override void Increment(int threadNum) 
    {
        // ...
        // method code that doesn't require exclusive access 
        lock(this)
        {
            Console.WriteLine(
                "Start Resource writing (Thread={0}) count: {1}", threadNum, count);
            int tempCount = count;
            Thread.Sleep(1000);
            tempCount++;
            count = tempCount;
            Console.WriteLine(
                "Stop Resource writing (Thread={0}) count: {1}", threadNum, count);
        }
        // rest of method code that doesn't require exclusive access
    }
}

class CounterUsingMutex : Counter
{
    Mutex m = new Mutex(); 

    public override int Read(int threadNum) 
    {
        // ...
        // method code that doesn't require exclusive access 
        m.WaitOne();
        try 
        {
            Console.WriteLine(
                "Start Resource reading (Thread={0})count: {1}", threadNum, count);
            Thread.Sleep(250);
            Console.WriteLine(
                "Stop Resource reading (Thread={0}) count: {1}", threadNum, count);
            return count;
        }
        finally 
        {
            m.ReleaseMutex();
        }
    }

    public override void Increment(int threadNum) 
    {
        // ...
        // method code that doesn't require exclusive access 
        m.WaitOne();
        try 
        {
            Console.WriteLine(
                "Start Resource writing (Thread={0}) count: {1}", threadNum, count);
            int tempCount = count;
            Thread.Sleep(1000);
            tempCount++;
            count = tempCount;
            Console.WriteLine(
                "Stop Resource writing (Thread={0}) count: {1}", threadNum, count);
        }
        finally 
        {
            m.ReleaseMutex();
        }
        // rest of method code that doesn't require exclusive access
    }
}

class CounterUsingReaderWriterLock : Counter
{
    ReaderWriterLock rwl = new ReaderWriterLock();

    public override int Read(int threadNum) 
    {
        // ...
        // method code that doesn't require exclusive access 
        rwl.AcquireReaderLock(Timeout.Infinite);
        try 
        {
            Console.WriteLine(
             "Start Resource reading (Thread={0})count: {1}", threadNum, count);
            Thread.Sleep(250);
            Console.WriteLine(
             "Stop Resource reading (Thread={0}) count: {1}", threadNum, count);
            return count;
        }
        finally 
        {
            rwl.ReleaseReaderLock();
        }
    }

    public override void Increment(int threadNum) 
    {
        // ...
        // method code that doesn't require exclusive access 
        rwl.AcquireWriterLock(Timeout.Infinite);
        try 
        {
            Console.WriteLine(
             "Start Resource writing (Thread={0}) count: {1}", threadNum, count);
            int tempCount = count;
            Thread.Sleep(1000);
            tempCount++;
            count = tempCount;
            Console.WriteLine(
             "Stop  Resource writing (Thread={0}) count: {1}", threadNum, count);
        }
        finally 
        {
            rwl.ReleaseWriterLock();
        }
        // rest of method code that doesn't require exclusive access
    }
}


class App 
{
    static Counter counter = null;
    static int totalNumberOfAsyncOps = 10;
    static int numAsyncOps = totalNumberOfAsyncOps;
    static AutoResetEvent asyncOpsAreDone = new AutoResetEvent(false);

    public static void Main() 
    {
        Console.WriteLine("\n\nUnsafe test:");
        asyncOpsAreDone.Reset();
        numAsyncOps = totalNumberOfAsyncOps;
        counter = new CounterUnsafe();
        for (int threadNum = 0; threadNum < numAsyncOps; threadNum++) 
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(UpdateResource), threadNum);
        }
        asyncOpsAreDone.WaitOne();
        Console.WriteLine("All Unsafe threads have completed.");
        
        
        Console.WriteLine("\n\nInterlocked test:");
        asyncOpsAreDone.Reset();
        numAsyncOps = totalNumberOfAsyncOps;
        counter = new CounterUsingInterlocked();
        for (int threadNum = 0; threadNum < totalNumberOfAsyncOps; threadNum++) 
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(UpdateResource), threadNum);
        }
        asyncOpsAreDone.WaitOne();
        Console.WriteLine("All Interlocked threads have completed.");


        Console.WriteLine("\n\nLock test:");
        asyncOpsAreDone.Reset();
        numAsyncOps = totalNumberOfAsyncOps;
        counter = new CounterUsingLock();
        for (int threadNum = 0; threadNum < numAsyncOps; threadNum++) 
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(UpdateResource), threadNum);
        }
        asyncOpsAreDone.WaitOne();
        Console.WriteLine("All Lock threads have completed.");

        Console.WriteLine("\n\nMutex test:");
        asyncOpsAreDone.Reset();
        numAsyncOps = totalNumberOfAsyncOps;
        counter = new CounterUsingMutex();
        for (int threadNum = 0; threadNum < numAsyncOps; threadNum++) 
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(UpdateResource), threadNum);
        }
        asyncOpsAreDone.WaitOne();
        Console.WriteLine("All Mutex threads have completed.");

    
        asyncOpsAreDone.Reset();
        numAsyncOps = totalNumberOfAsyncOps;
        counter = new CounterUsingReaderWriterLock();
        Console.WriteLine("\n\nReadWriteLock test:");
        for (int threadNum = 0; threadNum < numAsyncOps; threadNum++) 
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(UpdateResource), threadNum);
        }
        asyncOpsAreDone.WaitOne();
        Console.WriteLine("All ReadWriteLock threads have completed.");
        
    }


    // The callback method's signature MUST match that of a System.Threading.TimerCallback 
    // delegate (it takes an Object parameter and returns void)
    static void UpdateResource(Object state) 
    {
        int threadNum = (int) state;
        if ((threadNum % 2) != 0) counter.Read(threadNum);
        else counter.Increment(threadNum);

        if (( Interlocked.Decrement(ref numAsyncOps)) == 0)
            asyncOpsAreDone.Set();
    }
}