Detailed explanation of graphic code of Thread, Task, Async/Await, IAsyncResult in C#

This article mainly introduces the relevant knowledge of Thread, Task, Async/Await, IAsyncResult in C#. It has a certain reference value, let’s take a look with the editor below

Speaking of asynchronous, Thread, Task, async/await, IAsyncResult, these things are definitely unavoidable. Let’s talk about them in turn today.

1. Thread

The meaning of multi-threading is that in an application, multiple execution parts can be executed at the same time; for more time-consuming operations ( For example, io, Database operations), or waiting for a response (such as WCF communication) The operation can be performed by starting the background thread separately, so that the main thread will not be blocked and can continue to execute; wait until the background thread is completed, then notify the main thread, and then make the corresponding operation!

In C#! It is relatively simple to start a new thread in

static void Main(string[] args)
{
 Console.WriteLine("主线程开始");
 //IsBackground=true，将其设置为后台线程
 Thread t = new Thread(Run) { IsBackground = true };
 t.Start();
　　 Console.WriteLine("主线程在做其他的事！");
 //主线程结束，后台线程会自动结束，不管有没有执行完成
 //Thread.Sleep(300);
 Thread.Sleep(1500);
 Console.WriteLine("主线程结束");
}
static void Run()
{
 Thread.Sleep(700);
 Console.WriteLine("这是后台线程调用");
}

The execution result is as shown below,

You can see that after starting the background thread, the main thread continues to execute. It does not wait until the background thread is executed.

##1.1 Thread Pool

object in the asp.net processing mechanism),

for (int i = 0; i < 10; i++)
{
 ThreadPool.QueueUserWorkItem(m =>
 {
  Console.WriteLine(Thread.CurrentThread.ManagedThreadId.ToString());
 });
}
Console.Read();

#.

## 1.2 Semaphore Semaphore is responsible for coordinating threads and can limit the number of threads accessing a certain resource

Here is SemaphoreSlim A simple example of class usage:

 static SemaphoreSlim semLim = new SemaphoreSlim(3); //3表示最多只能有三个线程同时访问
static void Main(string[] args)
{
 for (int i = 0; i < 10; i++)
 {
  new Thread(SemaphoreTest).Start();
 }
 Console.Read();
}
static void SemaphoreTest()
{
 semLim.Wait();
 Console.WriteLine("线程" + Thread.CurrentThread.ManagedThreadId.ToString() + "开始执行");
 Thread.Sleep(2000);
 Console.WriteLine("线程" + Thread.CurrentThread.ManagedThreadId.ToString() + "执行完毕");
 semLim.Release();
}

The execution results are as follows:

It can be seen that only three threads are executing at the beginning , when a thread is executed and released, a new thread will execute the method!

In addition to the SemaphoreSlim class, you can also use the Semaphore class, which feels more flexible. If you are interested, you can search it. Demonstration is done!

Task was added to .NET4.0. It has similar functions to the thread pool ThreadPool. When you use Task to start a new task, it will be drawn from the thread pool. Calling thread, and Thread will create a new thread every time it is instantiated.

Console.WriteLine("主线程启动");
//Task.Run启动一个线程
//Task启动的是后台线程，要在主线程中等待后台线程执行完毕，可以调用Wait方法
//Task task = Task.Factory.StartNew(() => { Thread.Sleep(1500); Console.WriteLine("task启动"); });
Task task = Task.Run(() => { 
 Thread.Sleep(1500);
 Console.WriteLine("task启动");
});
Thread.Sleep(300);
task.Wait();
Console.WriteLine("主线程结束");

The execution results are as follows:

Method to start a new task: Task.Run() or Task.Factory.StartNew(), which opens the background Thread

To wait in the main thread for the background thread to complete execution, you can use the Wait method (it will be executed in a synchronous manner). Without Wait, it will be executed asynchronously.

Compare Task and Thread:

static void Main(string[] args)
{
 for (int i = 0; i < 5; i++)
 {
  new Thread(Run1).Start();
 }
 for (int i = 0; i < 5; i++)
 {
  Task.Run(() => { Run2(); });
 }
}
static void Run1()
{
 Console.WriteLine("Thread Id =" + Thread.CurrentThread.ManagedThreadId);
}
static void Run2()
{
 Console.WriteLine("Task调用的Thread Id =" + Thread.CurrentThread.ManagedThreadId);
}

Execution result:

It can be seen that using Thread directly will open 5 threads. Use Task (using thread pool) to open 3!

2.1 Task##Task is a Task with a return value, and TResult is the return value type.

Console.WriteLine("主线程开始");
//返回值类型为string
Task<string> task = Task<string>.Run(() => {
 Thread.Sleep(2000); 
 return Thread.CurrentThread.ManagedThreadId.ToString(); 
});
//会等到task执行完毕才会输出;
Console.WriteLine(task.Result);
Console.WriteLine("主线程结束");

The return value can be obtained through task.Result. If the background thread has not finished executing when the value is obtained, it will Wait for it to complete!

3. async/await

async/await was introduced in C# 5.0, first usage:

static void Main(string[] args)
{
 Console.WriteLine("-------主线程启动-------");
 Task<int> task = GetStrLengthAsync();
 Console.WriteLine("主线程继续执行");
 Console.WriteLine("Task返回的值" + task.Result);
 Console.WriteLine("-------主线程结束-------");
}
static async Task<int> GetStrLengthAsync()
{
 Console.WriteLine("GetStrLengthAsync方法开始执行");
 //此处返回的<string>中的字符串类型，而不是Task<string>
 string str = await GetString();
 Console.WriteLine("GetStrLengthAsync方法执行结束");
 return str.Length;
}
static Task<string> GetString()
{
　　 //Console.WriteLine("GetString方法开始执行")
 return Task<string>.Run(() =>
 {
  Thread.Sleep(2000);
  return "GetString的返回值";
 });
}

class Program
{
 static void Main(string[] args)
 {
  Console.WriteLine("主程序开始--------------------");
  int threadId;
  AsyncDemo ad = new AsyncDemo();
  AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);

  IAsyncResult result = caller.BeginInvoke(3000,out threadId, null, null);
  Thread.Sleep(0);
  Console.WriteLine("主线程线程 {0} 正在运行.",Thread.CurrentThread.ManagedThreadId)
  //会阻塞线程，直到后台线程执行完毕之后，才会往下执行
  result.AsyncWaitHandle.WaitOne();
  Console.WriteLine("主程序在做一些事情！！！");
  //获取异步执行的结果
  string returnValue = caller.EndInvoke(out threadId, result);
  //释放资源
  result.AsyncWaitHandle.Close();
  Console.WriteLine("主程序结束--------------------");
  Console.Read();
 }
}
public class AsyncDemo
{
 //供后台线程执行的方法
 public string TestMethod(int callDuration, out int threadId)
 {
  Console.WriteLine("测试方法开始执行.");
  Thread.Sleep(callDuration);
  threadId = Thread.CurrentThread.ManagedThreadId;
  return String.Format("测试方法执行的时间 {0}.", callDuration.ToString());
 }
}
public delegate string AsyncMethodCaller(int callDuration, out int threadId);

Stopwatch watch1 = new Stopwatch();
watch1.Start();
for (int i = 1; i <= 10; i++)
{
 Console.Write(i + ",");
 Thread.Sleep(1000);
}
watch1.Stop();
Console.WriteLine(watch1.Elapsed);
Stopwatch watch2 = new Stopwatch();
watch2.Start();
//会调用线程池中的线程
Parallel.For(1, 11, i =>
{
 Console.WriteLine(i + ",线程ID:" + Thread.CurrentThread.ManagedThreadId);
 Thread.Sleep(1000);
});
watch2.Stop();
Console.WriteLine(watch2.Elapsed);

List<int> list = new List<int>() { 1, 2, 3, 4, 5, 6, 6, 7, 8, 9 };
Parallel.ForEach<int>(list, n =>
{
 Console.WriteLine(n);
 Thread.Sleep(1000);
});

Action[] actions = new Action[] { 
 new Action(()=>{
  Console.WriteLine("方法1");
 }),
 new Action(()=>{
  Console.WriteLine("方法2");
 })
};
Parallel.Invoke(actions);