C#专题之线程

5.1 资源访问冲突问题

internal class StateObject
{private int state = 5;public void ChangeState(){if (state == 5){state++;Console.WriteLine("state: " + state + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state = 5;}
}

static void Main(string[] args)
{StateObject state = new StateObject();for (int i = 0; i < 100; i++){Thread t = new Thread(state.ChangeState);t.Start();}
}

解决——加锁

internal class StateObject
{private Object _lock = new Object();private int state = 5;public void ChangeState(){lock (_lock){if (state == 5){state++;Console.WriteLine("state: " + state + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state = 5;}}
}

异步委托的方式启动线程

static void Test()
{Console.WriteLine("Test Started");Console.WriteLine("Test Running");Thread.Sleep(3000);Console.WriteLine("Test Completed");
}delegate void TestDelegate();static void Main(string[] args)
{TestDelegate testDelegate = Test;testDelegate.BeginInvoke(null, null);Console.WtiteLine("Main Completed");
}

线程的优先级和线程的状态

线程的优先级

在 Thread 类中，可以设置 Priority 属性，以影响线程的基本优先级，Priority 属性是 ThreadPriority 枚举定义的一个值。定义的级别有：Highest、AboveNormal、Normal、BelowNormal 和 Lowest。

线程的状态

获取线程的状态（Running 还是 Unstarted…），当我们通过调用 Thread 对象的 Start() 方法，可以创建线程，但是调用了 Start() 方法之后，新线程不是马上进入 Running 状态，而是处于 Unstarted 状态，只有当操作系统的线程调度器选择了要运行的线程，这个线程的状态才会修改为 Running 状态。我们使用 Thread.Sleep() 方法可以让当前线程休眠进入 WaitSleepJoin 状态。
使用 Thread对象的 Abort() 方法可以停止线程。调用这个方法，会在要终止的线程中抛出一个 ThreadAbortException 类型的异常，我们可以 try catch 这个异常，然后在线程终止前做一些清理的工作。
如果需要等待线程的结束，可以调用 Thread 对象的 Join() 方法，表示把 Thread 加入进来，暂停当前线程，并把它设置为 WaitSleepJoin 状态，直到加入的线程完成为止。

线程池

static void Main(string[] args)
{for (int i = 0; i < 10; i++){ThreadPool.QueueUserWorkItem(Download);}Thrad.Sleep(500);
}static void Download(Object state)
{for (int i = 0; i < 3; i++){Console.WriteLine("Downloading...: " + Thread.CurrentThread.ManageThreadId);Thread.Sleep(100);}
}

使用线程池启动的线程默认是后台线程
如果进程的所有前台线程都结束了，所有的后台线程就会停止，不能把入池的线程改为前台线程。
不能给入池的线程设置优先级或名称
入池的线程只能用于时间较短的任务，如果线程要一直运行，就应该使用 Thread 类创建一个线程。

死锁问题

internal class StateObject
{private Object _lock1 = new Object();private Object _lock2 = new Object();private int state1 = 5;private int state2 = 5;public void ChangeState(){Console.WriteLine(Thread.CurrentThread.ManageThreadId + "拿到了第1把锁");lock (_lock1){lock (_lock2){Console.WriteLine(Thread.CurrentThread.ManageThreadId + "拿到了第2把锁");if (state1 == 5){state1++;Console.WriteLine("state: " + state1 + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state1 = 5;if (state2 == 5){state2++;Console.WriteLine("state: " + state2 + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state2 = 5;}}}public void ChangeState(){lock (_lock2){Console.WriteLine(Thread.CurrentThread.ManageThreadId + "拿到了第2把锁");lock (_lock1){Console.WriteLine(Thread.CurrentThread.ManageThreadId + "拿到了第1把锁");if (state1 == 5){state1++;Console.WriteLine("state: " + state1 + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state1 = 5;if (state2 == 5){state2++;Console.WriteLine("state: " + state2 + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state2 = 5;}}}
}

解决方法——规定相同的拿锁顺序

internal class StateObject
{private Object _lock1 = new Object();private Object _lock2 = new Object();private int state1 = 5;private int state2 = 5;public void ChangeState(){Console.WriteLine(Thread.CurrentThread.ManageThreadId + "拿到了第1把锁");lock (_lock1){lock (_lock2){Console.WriteLine(Thread.CurrentThread.ManageThreadId + "拿到了第2把锁");if (state1 == 5){state1++;Console.WriteLine("state: " + state1 + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state1 = 5;if (state2 == 5){state2++;Console.WriteLine("state: " + state2 + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state2 = 5;}}}public void ChangeState(){lock (_lock1){Console.WriteLine(Thread.CurrentThread.ManageThreadId + "拿到了第1把锁");lock (_lock2){Console.WriteLine(Thread.CurrentThread.ManageThreadId + "拿到了第2把锁");if (state1 == 5){state1++;Console.WriteLine("state: " + state1 + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state1 = 5;if (state2 == 5){state2++;Console.WriteLine("state: " + state2 + " 线程ID：" + Thread.CurrentThread.ManageThreadId);}state2 = 5;}}}
}

使用Thread启动线程和传输数据

启动线程

static void Test()
{Console.WriteLine("Test Started");Console.WriteLine("Test Running");Thread.Sleep(1000);Console.WriteLine("Test Completed");
}static void Main(string[] args)
{Thread t = new Thread(Test);t.Start();Console.WriteLine("Main Completed");
}

使用 Lambda 表达式：

static void Main(string[] args)
{Thread t = new Thread(() => Console.WriteLine("Child Thread: " + Thread.CurrentThread.ManageThreadId));t.Start();Console.WriteLine("Main Completed: " + Thread.CurrentThread.ManageThreadId);
}

使用匿名方法：

static void Main(string[] args)
{Thread t = new Thread(delegate () {Console.WriteLine("Child Thread: " + Thread.CurrentThread.ManageThreadId)});t.Start();Console.WriteLine("Main Completed: " + Thread.CurrentThread.ManageThreadId);
}

传递数据

static void Download(Object x)
{string str = o as string;Console.WriteLine(str);
}static void Main(string[] args)
{Thread t = new Thread(Download);t.Start("http://www.xxx.com");
}

Start() 方法只能接收无参的方法或只有一个参数的方法

传递多个数据

public struct Data
{public string message;public int age;
}static void Download(Object x)
{Data data = (Data)o;Console.WriteLine(data.message);Console.WriteLine(data.age);
}static void Main(string[] args)
{Data data = new Data();data.message = "";data.age = 12;  Thread t = new Thread(Download);t.Start(data);
}

任务

static void Main(string[] args)
{TaskFactory tf = new TaskFactory();Task t = tf.StartNew(Test);Thread.Sleep(5000);
}static void Test()
{for (int i = 0; i < 10000; i++){Console.WriteLine("A");}
}

static void Main(string[] args)
{Task t = new Task(Test);t.Start();Thread.Sleep(5000);
}static void Test()
{for (int i = 0; i < 10000; i++){Console.WriteLine("A");}
}

连续任务

如果一个任务t1的执行是依赖于另一个任务t2的，那么就需要在这个任务t2执行完毕后才开始执行t1。这个时候我们就可以使用连续任务。

static void FirstDownload()
{Console.WriteLine("Downloading ...");Thread.Sleep(2000);
}static void SecondAlert(Task t)
{Console.WriteLine("下载完成！");
}static void Main(string[] args)
{Task t1 = new Task(FirstDownload);t1.ContinueWith(SecondAlert);t1.Start();Thread.Sleep(5000);
}

static void FirstDownload()
{Console.WriteLine("Downloading ...");Thread.Sleep(2000);
}static void SecondAlert(Task t)
{Console.WriteLine("下载完成！");
}static void Main(string[] args)
{Task t1 = new Task(FirstDownload);Task t2 = t1.ContinueWith(SecondAlert);Task t3 = t2.ContinueWith(SecondAlert);t1.Start();Thread.Sleep(5000);