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
委托是方法的类型安全的引用
Delegate类还支持异步地调用方法。在后台，Delegate类会创建一个执行任务的线程
-
投票，并检查委托是否完成了任务
所创建的Delegate类提供了BeginInvoke()方法，该方法中，可以传递用委托类型定义的输入参数。
BeginInvoke()方法总是有AsyncCallback和Object类型的两个额外参数
BeginInvoke()方法返回类型：IAsyncResult
代码示例
static void Main(string[] args)
{
// synchronous method call
// TakesAWhile(1,3000);
// asynchronous by using a delegate
TakesAWhileDelegate dl = TakesAWhile;
IAsyncResult ar = dl.BeginInvoke(1, 500, null, null);
while (!ar.IsCompleted)
{
// doing something else in the main thread
Console.Write(".");
Thread.Sleep(50);
}
int result = dl.EndInvoke(ar);
Console.WriteLine("result:{0}", result);
}
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;
}
-
使用与IAsyncResult相关联的等待句柄
使用AsyncWaitHandle属性可以访问等待句柄
代码示例，在此将上述示例中的While循环更改一下即可，如下
while (true)
{
Console.Write(".");
if (ar.AsyncWaitHandle.WaitOne(50, false))
{
Console.WriteLine("Can get the result now");
break;
}
}
-
异步回调
在BeginInvoke()方法的第3个参数中，可以传递一个满足AsyncCallback委托的需求的方法
代码示例
TakesAWhileDelegate dl = TakesAWhile;
dl.BeginInvoke(1, 500, TakesAWhileCompleted, dl);
for (int i = 0; i < 100; i++)
{
Console.Write(".");
Thread.Sleep(50);
}
static void TakesAWhileCompleted(IAsyncResult ar)
{
if (ar == null)
throw new ArgumentNullException("ar");
TakesAWhileDelegate dl = ar.AsyncState as TakesAWhileDelegate;
Trace.Assert(dl != null, "Invalid object type");
int result = dl.EndInvoke(ar);
Console.WriteLine("result:{0}", result);
}
Thread类
Thread类可以创建和控制线程
默认情况，Thread类创建线程是前台线程。线程池中的线程总是后台线程。
只要有一个前台线程在运行，应用程序的进程就在运行。Thread类创建线程时，可以设置IsBackground属性，以确定该线程时前台线程还是后台线程
代码示例
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);
}
线程池
ThreadPool类托管，在需要时增减池中线程的线程数，直到最大的线程数
ThreadPool.QueueUserWorkItem()方法，传递一个WaitCallback类型的委托
代码示例
int nWorkerThreads;
int nCompletionPortThreads;
ThreadPool.GetMaxThreads(out nWorkerThreads, out nCompletionPortThreads);
Console.WriteLine("Max worker threads:{0},I/O completion threads:{1}",
nWorkerThreads, nCompletionPortThreads);
for (int i = 0; i < 5; i++)
{
ThreadPool.QueueUserWorkItem(JobForAThread);
}
static void JobForAThread(object state)
{
for (int i = 0; i < 3; i++)
{
Console.WriteLine("loop{0},running inside pooled thread{1}",
i, Thread.CurrentThread.ManagedThreadId);
Thread.Sleep(50);
}
}
任务
.NET 4包含新名称空间 System.Threading.Tasks，它包含的类抽象出了线程功能。在后台使用ThreadPool.
-
启动新任务
- 实例化TaskFactory类，在其中把TaskMethod()方法传递给StartNew()方法
- 使用Task类的构造函数，调用Task类的Start()方法
- 示例代码
//using task factory
TaskFactory tf = new TaskFactory();
Task t1 = tf.StartNew(TaskMethod);
//using the task factory via a task
Task t2 = Task.Factory.StartNew(TaskMethod);
//using Task constructor
Task t3 = new Task(TaskMethod);
t3.Start();
Task t4 = new Task(TaskMethod, TaskCreationOptions.PreferFairness);
t4.Start();
static void TaskMethod()
{
Console.WriteLine("running in a task");
Console.WriteLine("Task id:{0}", Task.CurrentId);
}
