浅谈C#之线程创建和管理

一、基本介绍

线程是一种并发执行的机制，允许程序同时执行多个任务。线程的使用使得我们能够利用计算机的多核处理器，实现程序的并行执行，提高系统的性能和响应能力。本文将详细介绍C#中线程的定义和使用方法，涵盖线程的创建、启动、同步和管理等方面。

线程管理是一个重要的概念，因为多线程编程可以帮助你提高应用程序的性能，特别是在执行耗时的操作时。

二、关键点

线程的创建与启动：
- 使用System.Threading.Thread类来创建线程。你可以通过继承Thread类并重写Run方法，或者直接传递一个委托给Thread类的构造函数来创建线程。
- 通过调用Thread.Start()方法来启动线程。
线程的同步：
- 使用lock语句来同步对共享资源的访问，防止多个线程同时修改同一个资源。
- Monitor类提供了更高级的同步功能，如等待、通知和超时。
线程池：
- 线程池是.NET Framework提供的一种机制，用于重用线程，减少创建和销毁线程的开销。
- 通过ThreadPool.QueueUserWorkItem方法将任务提交到线程池。
线程的生命周期管理：
- 线程有几种状态，如运行、等待、阻塞、死亡等。
- 可以使用Thread.Join()方法等待线程完成，或者使用Thread.Abort()方法强制终止线程（不推荐，因为它可能导致资源未正确释放）。
线程的优先级：
- 可以通过Thread.Priority属性设置线程的优先级，影响线程的调度顺序。
线程局部存储（Thread Local Storage, TLS）：
- 使用ThreadLocal<T>类可以为每个线程存储一个独立的值，这对于避免线程间的数据共享非常有用。
异步编程模型（APM）和任务并行库（TPL）：
- .NET Framework提供了异步编程模型，通过IAsyncResult接口和回调函数来实现异步操作。
- .NET 4.0引入了任务并行库（TPL），它提供了Task类和Parallel类，使得异步编程更加简单和强大。
CancellationToken：
- 用于在长时间运行的操作中提供取消机制，允许用户在操作完成前请求取消。
线程安全集合：
- .NET提供了一些线程安全的集合类，如ConcurrentDictionary，可以在多线程环境中安全地使用。
异常处理：
- 在多线程环境中，异常处理变得更加复杂，因为异常可能发生在不同的线程中。确保正确地捕获和处理线程中的异常。

三、示例代码

创建和启动线程

using System;
using System.Threading;class Program
{static void Main(){// 创建线程Thread thread = new Thread(new ThreadStart(ThreadMethod));thread.Start(); // 启动线程// 等待线程完成thread.Join();}static void ThreadMethod(){Console.WriteLine("Thread running...");}
}

线程同步

using System;
using System.Threading;class Program
{static object lockObject = new object();static int sharedResource = 0;static void Main(){Thread thread1 = new Thread(new ThreadStart(Increment));Thread thread2 = new Thread(new ThreadStart(Increment));thread1.Start();thread2.Start();thread1.Join();thread2.Join();Console.WriteLine($"Final value: {sharedResource}");}static void Increment(){for (int i = 0; i < 10000; i++){lock (lockObject){sharedResource++;}}}
}

使用线程池

using System;
using System.Threading;class Program
{static void Main(){ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork));ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork));Console.WriteLine("Main thread continues to run while work items are processed.");}static void DoWork(object stateInfo){Console.WriteLine("Work item starting...");Thread.Sleep(2000); // 模拟耗时操作Console.WriteLine("Work item finishing...");}
}

线程的生命周期管理

using System;
using System.Threading;class Program
{static void Main(){Thread thread = new Thread(new ThreadStart(ThreadMethod));thread.Start();Console.WriteLine("Main thread waiting for thread to complete...");thread.Join(); // 等待线程完成Console.WriteLine("Thread has completed.");}static void ThreadMethod(){Console.WriteLine("Thread running...");Thread.Sleep(5000); // 模拟耗时操作}
}

线程优先级

using System;
using System.Threading;class Program
{static void Main(){Thread thread = new Thread(new ThreadStart(ThreadMethod));thread.Priority = ThreadPriority.AboveNormal;thread.Start();}static void ThreadMethod(){Console.WriteLine("Thread running with priority: " + Thread.CurrentThread.Priority);}
}

线程局部存储

using System;
using System.Threading;class Program
{static ThreadLocal<int> threadLocalValue = new ThreadLocal<int>(() => 0);static void Main(){Thread thread1 = new Thread(new ThreadStart(ThreadMethod));Thread thread2 = new Thread(new ThreadStart(ThreadMethod));thread1.Start();thread2.Start();thread1.Join();thread2.Join();}static void ThreadMethod(){threadLocalValue.Value++;Console.WriteLine($"Thread {Thread.CurrentThread.ManagedThreadId} has value: {threadLocalValue.Value}");}
}

异步编程模型（APM）

using System;
using System.Threading;class Program
{static void Main(){AsyncResult result = new AsyncResult();result.BeginInvoke(DoWork, result);Console.WriteLine("Main thread continues to run...");result.AsyncWaitHandle.WaitOne(); // 等待异步操作完成Console.WriteLine("Work completed.");}static void DoWork(IAsyncResult ar){AsyncResult result = (AsyncResult)ar;result.EndInvoke();Console.WriteLine("Work item completed.");}
}public class AsyncResult : IAsyncResult
{public object AsyncState { get; private set; }public WaitHandle AsyncWaitHandle { get; private set; }public bool CompletedSynchronously => false;public bool IsCompleted { get; private set; }public AsyncResult(){AsyncState = null;AsyncWaitHandle = new ManualResetEvent(false);}public void BeginInvoke(Action callback, object state){AsyncState = state;ThreadPool.QueueUserWorkItem(_ =>{DoWork();if (callback != null){callback();}IsCompleted = true;AsyncWaitHandle.Set();});}public void EndInvoke(){AsyncWaitHandle.WaitOne();}private void DoWork(){Console.WriteLine("Work item starting...");Thread.Sleep(2000); // 模拟耗时操作Console.WriteLine("Work item finishing...");}
}

任务并行库（TPL）

using System;
using System.Threading.Tasks;class Program
{static async Task Main(){Task task1 = Task.Run(() => DoWork());Task task2 = Task.Run(() => DoWork());await Task.WhenAll(task1, task2);Console.WriteLine("Main thread continues to run while tasks are processed.");}static void DoWork(){Console.WriteLine("Task starting...");Thread.Sleep(2000); // 模拟耗时操作Console.WriteLine("Task finishing...");}
}

CancellationToken

using System;
using System.Threading;
using System.Threading.Tasks;class Program
{static async Task Main(){CancellationTokenSource cts = new CancellationTokenSource();CancellationToken token = cts.Token;Task task = Task.Run(() => DoWork(token), token);Console.WriteLine("Press any key to cancel the task...");Console.ReadKey();cts.Cancel();try{await task;}catch (OperationCanceledException){Console.WriteLine("Task was canceled.");}}static void DoWork(CancellationToken token){for (int i = 0; i < 5; i++){if (token.IsCancellationRequested){Console.WriteLine("Task was canceled.");break;}Console.WriteLine($"Task is running... {i}");Thread.Sleep(1000);}}
}

线程安全集合

using System;
using System.Collections.Concurrent;
using System.Threading;class Program
{static ConcurrentBag<int> concurrentBag = new ConcurrentBag<int>();static void Main(){Thread thread1 = new Thread(new ThreadStart(AddNumbers));Thread thread2 = new Thread(new ThreadStart(AddNumbers));thread1.Start();thread2.Start();thread1.Join();thread2.Join();Console.WriteLine($"Total numbers: {concurrentBag.Count}");}static void AddNumbers(){for (int i = 0; i < 10000; i++){concurrentBag.Add(i);}}
}