C# 编程中互斥锁的使用

C# 中的互斥锁

互斥锁是 C# 中使用的同步原语，用于控制多个线程或进程对共享资源的访问。其目的是确保在任何给定时间只有一个线程或进程可以获取互斥锁，从而提供互斥。

C# 中互斥锁的优点

可以使用互斥锁 (Mutex) 并享受其带来的好处。

1. 共享资源的独占访问

场景：多个线程或进程需要独占访问共享资源（例如文件、数据库或硬件设备）的情况。
示例：考虑一个多线程应用程序，其中多个线程需要同时写入共享日志文件。
好处：利用互斥锁，可以保证一次只有一个线程或进程可以访问资源，从而防止数据损坏或竞争条件。

2.跨进程同步

场景：不同进程中运行的线程之间需要同步。
示例：协调多个进程对共享内存映射文件的访问。
好处：互斥锁可以被命名并在整个系统范围内使用，从而实现跨进程边界的同步。

3. 关键部分保护

场景：代码的关键部分需要防止被多个线程并发执行的情况。
示例：考虑一个缓存实现，其中添加或删除项目必须是线程安全的。
好处：通过使用互斥锁，它有助于对关键部分的访问进行序列化，确保一次只有一个线程执行受保护的代码，从而避免竞争条件。

4. 资源池化

场景：管理对有限资源池（例如数据库连接或网络套接字）的访问时。
示例：多个线程竞争可用连接的连接池。
好处：可以使用互斥锁 (Mutex) 来控制对池的访问，从而保证同时使用的用户数量不超过池的容量。

5.避免死锁

场景：在多个同步原语一起使用以防止发生死锁的情况下。
示例：实现一个需要原子锁定多个资源的事务系统。
好处：互斥锁可以参与死锁避免策略，有助于防止死锁情况的发生。

互斥锁的实现

步骤1.

使用Xaml View测试所有情况。

<Window x:Class="MutexExample.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:d="http://schemas.microsoft.com/expression/blend/2008"xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"xmlns:local="clr-namespace:MutexExample"mc:Ignorable="d"Title="MainWindow" Height="450" Width="800"><Grid><StackPanel Orientation="Vertical"><Button x:Name="BtnSR" Height="30" Content="Shared Resource" Margin="10" Click="BtnSR_Click"/><Button x:Name="BtnCPS" Height="30" Content="Cross-Process Synchronization" Margin="10" Click="BtnCPS_Click"/><Button x:Name="BtnCSP" Height="30" Content="Critical Section Protection" Margin="10" Click="BtnCSP_Click"/><Button x:Name="BtnRP" Height="30" Content="Resource Pooling" Margin="10" Click="BtnRP_Click"/><Button x:Name="BtnDLA" Height="30" Content="Deadlock Avoidance" Margin="10" Click="BtnDLA_Click"/></StackPanel></Grid>
</Window>

后端编程

using System;
using System.Threading;
using System.Windows;namespace MutexExample
{public partial class MainWindow : Window{Mutex mutex = new Mutex();static int availableResources = 3;public MainWindow(){InitializeComponent();}private void SharedResourceAccess(object id){mutex.WaitOne(); // Acquire the mutextry{Console.WriteLine($"Thread {id} is accessing the shared resource...");// Simulate some workThread.Sleep(2000);}finally{mutex.ReleaseMutex(); // Release the mutex}}private void BtnSR_Click(object sender, RoutedEventArgs e){// Create multiple threads accessing the shared resourcefor (int i = 0; i < 5; i++){Thread thread = new Thread(SharedResourceAccess);thread.Start(i);}}private void BtnCPS_Click(object sender, RoutedEventArgs e){// Acquire the mutexif (mutex.WaitOne(TimeSpan.FromSeconds(5))){try{Console.WriteLine("Process 1 has acquired the mutex.");Console.ReadLine(); // Hold the mutex until Enter is pressed}finally{mutex.ReleaseMutex(); // Release the mutex}}else{Console.WriteLine("Process 1 failed to acquire the mutex.");}}private void CriticalSectionAccess(object id){mutex.WaitOne(); // Acquire the mutextry{Console.WriteLine($"Thread {id} is executing the critical section...");// Simulate some workThread.Sleep(2000);}finally{mutex.ReleaseMutex(); // Release the mutex}}private void BtnCSP_Click(object sender, RoutedEventArgs e){// Create multiple threads accessing a critical sectionfor (int i = 0; i < 5; i++){Thread thread = new Thread(CriticalSectionAccess);thread.Start(i);}}private void ResourceAccess(object id){mutex.WaitOne(); // Acquire the mutextry{if (availableResources > 0){availableResources--;Console.WriteLine($"Thread {id} acquired a resource. Remaining resources: {availableResources}");// Simulate some workThread.Sleep(2000);availableResources++;}else{Console.WriteLine($"Thread {id} could not acquire a resource. No resources available.");}}finally{mutex.ReleaseMutex(); // Release the mutex}}private void BtnRP_Click(object sender, RoutedEventArgs e){// Create multiple threads to access the resource poolfor (int i = 0; i < 5; i++){Thread thread = new Thread(ResourceAccess);thread.Start(i);}}private void BtnDLA_Click(object sender, RoutedEventArgs e){Thread thread1 = new Thread(Thread1);Thread thread2 = new Thread(Thread2);thread1.Start();thread2.Start();thread1.Join();thread2.Join();}private Mutex mutex1 = new Mutex();private Mutex mutex2 = new Mutex();private void Thread1(){mutex1.WaitOne();Console.WriteLine("Thread 1 acquired mutex1");Thread.Sleep(1000);mutex2.WaitOne();Console.WriteLine("Thread 1 acquired mutex2");mutex2.ReleaseMutex();mutex1.ReleaseMutex();}private void Thread2(){mutex2.WaitOne();Console.WriteLine("Thread 2 acquired mutex2");Thread.Sleep(1000);mutex1.WaitOne();Console.WriteLine("Thread 2 acquired mutex1");mutex1.ReleaseMutex();mutex2.ReleaseMutex();}}
}