C# 线程、任务和同步

1，线程概述
线程是程序汇中独立的指令流。线程有一个优先级，实际上正在处理的程序的位置计数器，一个存储其局部变量的栈。每个线程都有自己的栈。但应用程序的内存和堆由一个进程的所有线程共享。
进程包含资源，如windows句柄，文件句柄或其他内核对象。每个进程都分配了虚拟内存。一个进程至少包含一个线程。操作系统会调度线程。

总结：
同步代码区域(代码块)：lock,  Monitor, SpinLock, Mutex,WaitHandle,Semaphore,EventWaitHandle,AutoRestEvent/ManualResetEvent.
Barrier, ReadWriterLock(Slim)
多线程变量同步：InterLocked, 

进程间同步：
Mutex, Semaphore,

2，异步委托：
创建线程的一种简单方式是定义一个委托，并异步调用它。委托时方法类型安全的引用。Delegate类还支持异步调用委托，在后头创建一个执行任务的线程。
　　委托使用线程池来完成异步调用。
　　public delegate int TakesAWhileDelegate(int data, int ms);
2.1投票：
　　IAsyncResult ar=al.BeginInvoke(1,3000, null, null);
      int result=dl.EndInvoke(ar);
2.2 等待句柄  (WaitHandle)

    class Program
    {
        public delegate int TakesAWhileDelegate(int data, int ms);
        static int TakesAWhile(int data, int ms)
        {
            Console.WriteLine("TakesAWhile started");
            Thread.Sleep(ms);
            Console.WriteLine("TakesAWhile completed");
            return ++data;
        }
        private static void Main(string[] args)
        {
            Console.WriteLine("Main Begin.");
            TakesAWhileDelegate dl = TakesAWhile;
            IAsyncResult ar = dl.BeginInvoke(2, 3000, null, null);

            //ar.IsCompleted
            //ar.AsyncWaitHandle.WaitOne(50)

            dl.EndInvoke(ar);
            Console.WriteLine("Main() end.");
            Console.ReadLine();
        }
    }

2.3 异步回调 (dl.BeginInvoke(1,3000, TakesAWhileCompleted, dl) )
传入一个回调函数委托，来异步执行。

    class Program
    {
        public delegate int TakesAWhileDelegate(int data, int ms);
        static int TakesAWhile(int data, int ms)
        {
            Console.WriteLine("TakesAWhile started");
            Thread.Sleep(ms);
            Console.WriteLine("TakesAWhile completed");
            return ++data;
        }
        private static void Main(string[] args)
        {
            Console.WriteLine("Main Begin.");
            TakesAWhileDelegate dl = TakesAWhile;
            dl.BeginInvoke(2, 3000, ar =>
            {
                if (ar == null)
                    throw new ArgumentNullException("ar");
                TakesAWhileDelegate dl1 = ar.AsyncState as TakesAWhileDelegate;
                Trace.Assert(dl1 != null, "Invalid object type");
                int result = dl1.EndInvoke(ar);
                Console.WriteLine("result: {0}", result);
            }, null);

            Console.WriteLine("Main() end.");
            Console.ReadLine();
        }
    }

3，Thread类
3.1 给线程传递数据
　　1，使用带ParameterizedThreadStart委托参数的Thread构造函数。2，创建自定义类，把线程的方法定位实例方法，这样就可以初始化实例的数据，之后启动线程。
3.2 后台线程：
　　只要有一个前台线程在运行，应用程序的进程就在运行。如果多个前台线程在运行，而Main()方法结束了，应用程序的进程依然是激活的，直到所有前台线程完成其任务为止。
　　

        private static void Main(string[] args)
        {
            var t1 = new Thread(ThreadMain) {Name = "MyNewThread", IsBackground = false};
            t1.Start();
            Console.WriteLine("Main Thread ending now.");

        }

        static void ThreadMain()
        {
            Console.WriteLine("Thread {0} started", Thread.CurrentThread.Name);
            Thread.Sleep(3000);
            Console.WriteLine("Thread {0} Completed",Thread.CurrentThread.Name);
        }

3.3 线程的优先级 

4 线程池

5，任务
5.1 启动任务：
　　

启动任务代码

            TaskFactory tf = new TaskFactory();
            Task t1 = tf.StartNew(TaskMethod);

            Task t2 = Task.Factory.StartNew(TaskMethod);

            Task t3 = new Task(TaskMethod);
            t3.Start();

 5.2 连续的任务
Task t1=new Task(DoOnFirst);
Task t2=t1.ContinueWith(DoOnSecond);

5.3任务层次结构


6 Parallel 类
Parallel.For
Parallel.ForEach()
Parallel.Invoke(fun1,fun2);

        private static void Main(string[] args)
        {
            Parallel.Invoke(TaskMethod1,TaskMethod2);

            Console.ReadLine();
        }

        static void TaskMethod1()
        {
            Console.WriteLine("1running in a task.");
            Console.WriteLine("Task id: {0}", Task.CurrentId);
        }
        static void TaskMethod2()
        {
            Console.WriteLine("2running in a task.");
            Console.WriteLine("Task id: {0}", Task.CurrentId);
        }

7. 取消架构

8， 线程问题：  争用条件和死锁
8.1 争用条件：

        public class StateObject
        {
            private int state = 5;

            public void ChangeState(int loop)
            {
                lock (this)
                {
                    if (state == 5)
                    {
                        state++;
                        Trace.Assert(state == 6, "Race condition ocurred after " + loop + " loops  " + Task.CurrentId);
                        if (loop % 1000000 == 0)
                        {
                            Console.WriteLine("after " + loop + " loops  " + Task.CurrentId);
                        }
                    }
                    state = 5;
                }

            }
        }

        public class SampleTask
        {
            public void RaceCondition(object o)
            {
                Trace.Assert(o is StateObject, "o must be of type StateObject.");
                StateObject state = o as StateObject;
                int i = 0;
                while (true)
                {
                    state.ChangeState(i++);
                }
            }
        }

        public class SampleThread
        {
            public SampleThread(StateObject s1, StateObject s2)
            {
                this.s1 = s1;
                this.s2 = s2;
            }

            private StateObject s1;
            private StateObject s2;

            public void Deadlock1()
            {
                int i = 0;
                while (true)
                {
                    lock (s1)
                    {
                        lock (s2)
                        {
                            s1.ChangeState(i);
                            s2.ChangeState(i++);
                            Console.WriteLine("still running, {0}", i);

                        }
                    }
                    //Thread.Yield();
                }
            }
            public void Deadlock2()
            {
                int i = 0;
                while (true)
                {
                    lock (s2)
                    {
                        lock (s1)
                        {
                            s1.ChangeState(i);
                            s2.ChangeState(i++);
                            Console.WriteLine("still running, {0}", i);

                        }
                    }
                    //Thread.Yield();
                }
            }
        }

        private static void Main(string[] args)
        {
            var state1 = new StateObject();
            var state2 = new StateObject();

            SampleThread st = new SampleThread(state1, state2);

            Task.Factory.StartNew(st.Deadlock1);
            Task.Factory.StartNew(st.Deadlock2);

            Console.ReadLine();
        }

9, 同步
9.1 Lock 语句
栈是线程独立的，但不是私有的。所有线程的栈内所有内容，都可以被其他线程访问。
为什么不用 lock(this) ?
因为这通常超出我们的控制，因为其他人也有可能lock这个对象。一个私有的对象是更好的选择。避免lock一个公开类型，或者超出你代码的控制的实例。
Tips:可以提供线程安全的原子操作。

    class Program
    {
        public class SharedState
        {
            public int State { get; set; }
        }

        public class Job
        {
            private SharedState sharedState;

            public Job(SharedState sharedState)
            {
                this.sharedState = sharedState;
            }

            public void DoTheJob()
            {
                for (int i = 0; i < 50000; i++)
                {
                    sharedState.State +=1;
                }
            }
        }

        private static void Main(string[] args)
        {
            int numTasks = 20
                ;
            var state = new SharedState();
            var tasks = new Task[numTasks];
            for (int j = 0; j < 5; j++)
            {
                state.State = 0;
                for (int i = 0; i < numTasks; i++)
                {
                    tasks[i] = new Task(new Job(state).DoTheJob);
                    tasks[i].Start();

                }

                for (int i = 0; i < numTasks; i++)
                {
                    tasks[i].Wait();

                }
                Console.WriteLine("summarized {0}", state.State);
            }


        }

    }

9.2 Interlocked类
Interlock类用于使变量的简单语句原子化，线程安全方式递增、递减、交换和读取。i++不是线程安全的(包含3个操作：从内存获取、递增1、存储回内存，这些操作都可以被线程调度器打断)。

9.3 Monitor类
lock语句由编译器解释为Monitor类： Moniter.Enter(obj) ;   Monitor.Exit(obj);
Monitor类的一个优点：可以添加一个等待被锁定的超市值。Monitor.TryEnter(lockObj,500,ref lockToken);

            public void DoTheJob()
            {
                for (int i = 0; i < 50000; i++)
                {
                    bool isLocked = false;
                    goLabel:
                    Monitor.TryEnter(sharedState, 500, ref isLocked);
                    if (isLocked)
                    {
                        sharedState.State += 1;
                        Monitor.Exit(sharedState);
                    }
                    else
                    {
                        Console.WriteLine("lock failed.");
                        goto goLabel;
                    }

                }
            }

 9.4 SpinLock结构
适合于有大量的锁定，而且锁定的时间非常短。用法非常接近于Monitor类。获得锁使用Enter()或者TryEnter()，释放锁使用Exit()方法。小心SpinLock的传送，因为是结构，所以会复制。

9.5 WaitHandle基类
Delegate BeginInvoke() 用waithandle.WaitOne(50,false)来bolck当前线程,
WaitHandle是一个抽象基类，用于等待一个信号量的设置。可以等待不同的信号，因为WaitHandle是一个基类，可以派生一些类。

        private static void Main(string[] args)
        {
            Action ac = () =>
            {
                Console.WriteLine("Action Begin.");
                Thread.Sleep(2000);
                Console.WriteLine("Action End.");

            };

            AsyncCallback callback = (o) =>
            {
                var cb = (Action)o.AsyncState;
                cb.EndInvoke(o);
                Console.WriteLine("Callback finished.");

            };

            IAsyncResult ar = ac.BeginInvoke(callback, ac);
            while (true)
            {
                Console.Write(".");
                if (ar.AsyncWaitHandle.WaitOne(50, true))
                {
                    Console.WriteLine("Can get the result now.");
                    break;
                }
            }


            Console.ReadLine();

        }

WaitOne() 等待一个，waitAll()等待多个对象，WaitAny等待多个对象的一个。WaitAll和WaitAny是静态方法。

WaitHandle基类有一个SafeWaitHandle属性,其中可以将本机句柄赋予一个操作系统资源，并等待该句柄。
Mutex、EventWaitHandle 和 Semaphore类继承自WaitHandle基类。所以可以等到使用它们。

9.6 Mutex类
Mutex(mutual exclusion，互斥)是.net Framework中提供多个集成同步访问的一个类。它非常类似于Monitor,只有一个线程能拥有锁定。只有一个线程能获得互斥锁定，访问受互斥访问的同步代码区域。
    在Mutex类的构造函数中，可以指定互斥是否最初由主调线程拥有。定义互斥的名称，获得互斥是否存在的信息。
系统能识别有名称的Mutex

        private static void Main(string[] args)
        {
            bool isNew;
            using (Mutex mutex = new Mutex(false, "ProMutext", out isNew))
            {
                if (isNew)
                {
                    Console.WriteLine("Get mutex lock.");

                }
                else
                {
                    Console.WriteLine("can't get mutex lock.");
                }
                Thread.Sleep(3000);
            }
            Thread.Sleep(1000000);
            Console.ReadLine();

        }

9.7 Semaphore类
信号量非常类似于互斥，其区别是多个线程使用。信号量是一种技术的互斥锁定。使用信号量可以定义同时访问旗语锁定保护的资源的线程个数。
Semaphore类：可以命名，使用系统范围内的资源，允许不同进程间同步。

        static void Main()
        {
            int threadCount = 6;
            int semaphoreCount = 4;
            var semaphore = new Semaphore( semaphoreCount, semaphoreCount,"ProSemaphore");
            var threads = new Thread[threadCount];

            for (int i = 0; i < threadCount; i++)
            {
                threads[i] = new Thread(ThreadMain);
                threads[i].Start(semaphore);
            }

            for (int i = 0; i < threadCount; i++)
            {
                threads[i].Join();
            }
            Console.WriteLine("All threads finished");

        }

        static void ThreadMain(object o)
        {
            Semaphore semaphore = o as Semaphore;
            Trace.Assert(semaphore != null, "o must be a Semaphore type");
            bool isCompleted = false;
            while (!isCompleted)
            {
                if (semaphore.WaitOne(600))
                {
                    try
                    {
                        Console.WriteLine("Thread {0} locks the semaphore",
                              Thread.CurrentThread.ManagedThreadId);
                        Thread.Sleep(4000);
                    }
                    finally
                    {
                        semaphore.Release();
                        Console.WriteLine("Thread {0} releases the semaphore",
                           Thread.CurrentThread.ManagedThreadId);
                        isCompleted = true;
                    }
                }
                else
                {
                    Console.WriteLine("Timeout for thread {0}; wait again",
                       Thread.CurrentThread.ManagedThreadId);
                }
            }
        }

SemaphoreSlim类是对于较短等待时间进行了优化的轻型版本，不能跨进程。不能命名，不使用内核信号量，不能跨进程。

        private static void Main(string[] args)
        {
            int threadCount = 6;
            int semaphoreCount = 4;
            var semaphore = new SemaphoreSlim(semaphoreCount, semaphoreCount);
            Thread[] threads = new Thread[threadCount];

            for (int i = 0; i < threadCount; i++)
            {
                threads[i] = new Thread(ThreadMain);
                threads[i].Start(semaphore);
            }

            for (int i = 0; i < threadCount; i++)
            {
                threads[i].Join();
            }
            Console.WriteLine("AllThread finished!");

            Console.ReadLine();
        }

        static void ThreadMain(object o)
        {
            SemaphoreSlim semaphore = o as SemaphoreSlim;
            Trace.Assert(semaphore != null, "o must be a Semphore type.");
            bool isCompleted = false;
            while (!isCompleted)
            {
                if (semaphore.Wait(100))
                {
                    try
                    {
                        Console.WriteLine("thread {0} locks the semaphore", Thread.CurrentThread.ManagedThreadId);
                        Thread.Sleep(3000);
                    }
                    finally
                    {
                        semaphore.Release();
                        Console.WriteLine("Thread {0} release the semaphore", Thread.CurrentThread.ManagedThreadId);
                        isCompleted = true;
                    }
                }
                else
                {
                    Console.WriteLine("Timeout for thread {0}; wait again ", Thread.CurrentThread.ManagedThreadId);
                }
            }
        }

9.8 Event类
事件是另一个系统范围内的资源同步方法。为了从托管代码中使用系统事件，.net framework提供了ManualResetEvent、AutoResetEvent、ManualResetEventSlim和CountdownEvent类。

       private static void Main(string[] args)
        {
            const int taskCount = 10;
            var mEvents = new ManualResetEventSlim[taskCount];
            var waitHandles = new WaitHandle[taskCount];
            var calcs = new Calculator[taskCount];
            TaskFactory taskFactory = new TaskFactory();
            for (int i = 0; i < taskCount; i++)
            {
                mEvents[i] = new ManualResetEventSlim(false);
                waitHandles[i] = mEvents[i].WaitHandle;
                calcs[i] = new Calculator(mEvents[i]);

                taskFactory.StartNew(calcs[i].Calculation, Tuple.Create(i + 1, i + 3));

            }

            for (int i = 0; i < taskCount; i++)
            {
                int index = WaitHandle.WaitAny(waitHandles);
                if (index == WaitHandle.WaitTimeout)
                {
                    Console.WriteLine("Timeout!!");

                }
                else
                {
                    mEvents[index].Reset();
                    Console.WriteLine("finished task for {0}, result: {1}", index, calcs[index].Result);
                    Thread.Sleep(100);
                }
            }

            Console.ReadLine();
        }

        public class Calculator
        {
            private ManualResetEventSlim mEvent;
            public int Result { get; private set; }

            public Calculator(ManualResetEventSlim ev)
            {
                this.mEvent = ev;
            }

            public void Calculation(Object obj)
            {
                Tuple<int, int> data = (Tuple<int, int>)obj;
                Console.WriteLine("Task {0} starts calculation", Task.CurrentId);
                Thread.Sleep((3000));
                Result = data.Item1 + data.Item2;
                Console.WriteLine("Task {0} is ready", Task.CurrentId);
                mEvent.Set();
            }
        }

把任务分支到多个任务中，并在以后合并结果，使用新的CountdownEvent类很有用。
不需要位每个任务创建一个单独的事件对象，而只需要创建一个事件对象。

var mEvents = new ManualResetEventSlim[taskCount];
// var cEvent = new CountdownEvent(taskCount);

var waitHandles = new WaitHandle[taskCount];
var calcs = new Calculator[taskCount];

int index = WaitHandle.WaitAny(waitHandles);//wait

//tasks
mEvent.Set();//all thread set;
//continue

        private static void Main(string[] args)
        {
            const int taskCount = 10;
            var cEvent = new CountdownEvent(taskCount);

            var calcs = new Calculator[taskCount];
            TaskFactory taskFactory = new TaskFactory();
            for (int i = 0; i < taskCount; i++)
            {
                calcs[i] = new Calculator(cEvent);

                taskFactory.StartNew(calcs[i].Calculation, Tuple.Create(i + 1, i + 3));

            }

            cEvent.Wait();
            Console.WriteLine("All finished.");

            Console.ReadLine();
        }

        public class Calculator
        {
            private CountdownEvent cEvent;
            public int Result { get; private set; }

            public Calculator(CountdownEvent ev)
            {
                this.cEvent = ev;
            }

            public void Calculation(Object obj)
            {
                Tuple<int, int> data = (Tuple<int, int>)obj;
                Console.WriteLine("Task {0} starts calculation", Task.CurrentId);
                Thread.Sleep((3000));
                Result = data.Item1 + data.Item2;
                Console.WriteLine("Task {0} is ready", Task.CurrentId);
                cEvent.Signal();
            }
        }

 9.9 Barrier 类
适合于工作有多个任务分支且以后又需要合并工作的情况。

 var barrier = new Barrier(numberTasks + 1);
 barrier.SignalAndWait();//wait
//tasks
barrier.RemoveParticipant();//2 left

barrier.RemoveParticipant();//1 left

//continue.

9.10 ReadWriterLockSlim类
允许多个读取器。同时只有一个写入器工作，此时读取器不能工作。

        private static List<int> items = new List<int>() { 0, 1, 2, 3, 4, 5 };
        static ReaderWriterLockSlim rwl = new ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion);

        static void ReadMethod(object reader)
        {
            try
            {
                rwl.EnterReadLock();
                for (int i = 0; i < items.Count; i++)
                {
                    Console.WriteLine("read {0}, loop: {1}, item:{2}", reader, i, items[i]);
                    Thread.Sleep(40);
                }
            }
            finally
            {
                rwl.ExitReadLock();
            }
        }

        static void WriterMethod(object writer)
        {
            try
            {
                while (!rwl.TryEnterWriteLock(50))
                {
                    Console.WriteLine("Writer {0} waiting ,current reader count: {1}", writer, rwl.CurrentReadCount);
                }
                Console.WriteLine("Writer{0} acquired the lock.", writer);
                for (int i = 0; i < items.Count; i++)
                {
                    items[i]++;
                    Thread.Sleep(50);

                }
                Console.WriteLine("Writer {0} finished.", writer);

            }
            finally
            {
                rwl.ExitWriteLock();
            }
        }
        private static void Main(string[] args)
        {
            var taskFactory = new TaskFactory(TaskCreationOptions.LongRunning, TaskContinuationOptions.None);
            var tasks = new Task[6];
            tasks[0] = taskFactory.StartNew(WriterMethod, 1);
            tasks[1] = taskFactory.StartNew(ReadMethod, 1);
            tasks[2] = taskFactory.StartNew(ReadMethod, 2);
            tasks[3] = taskFactory.StartNew(WriterMethod, 2);
            tasks[4] = taskFactory.StartNew(ReadMethod, 3);
            tasks[5] = taskFactory.StartNew(ReadMethod, 4);
            foreach (Task task in tasks)
            {
                task.Wait();

            }


            Console.WriteLine("All finished.");

            Console.ReadLine();
        }

10 Timer类