Question

Mutex课程被误解了，而Global mutex则更是如此。

创建全局互斥锁时使用什么是好的，安全的模式？

一个可行的

无论我的机器位于
保证正确释放互斥锁
如果未获取互斥锁，则可选择不会永久挂起
处理其他进程放弃互斥锁的情况

Answer 1

我想确保它在那里，因为它很难做对：

using System.Runtime.InteropServices;   //GuidAttribute
using System.Reflection;                //Assembly
using System.Threading;                 //Mutex
using System.Security.AccessControl;    //MutexAccessRule
using System.Security.Principal;        //SecurityIdentifier

static void Main(string[] args)
{
    // get application GUID as defined in AssemblyInfo.cs
    string appGuid =
        ((GuidAttribute)Assembly.GetExecutingAssembly().
            GetCustomAttributes(typeof(GuidAttribute), false).
                GetValue(0)).Value.ToString();

    // unique id for global mutex - Global prefix means it is global to the machine
    string mutexId = string.Format( "Global\\{{{0}}}", appGuid );

    // Need a place to store a return value in Mutex() constructor call
    bool createdNew;

    // edited by Jeremy Wiebe to add example of setting up security for multi-user usage
    // edited by 'Marc' to work also on localized systems (don't use just "Everyone") 
    var allowEveryoneRule =
        new MutexAccessRule( new SecurityIdentifier( WellKnownSidType.WorldSid
                                                   , null)
                           , MutexRights.FullControl
                           , AccessControlType.Allow
                           );
    var securitySettings = new MutexSecurity();
    securitySettings.AddAccessRule(allowEveryoneRule);

   // edited by MasonGZhwiti to prevent race condition on security settings via VanNguyen
    using (var mutex = new Mutex(false, mutexId, out createdNew, securitySettings))
    {
        // edited by acidzombie24
        var hasHandle = false;
        try
        {
            try
            {
                // note, you may want to time out here instead of waiting forever
                // edited by acidzombie24
                // mutex.WaitOne(Timeout.Infinite, false);
                hasHandle = mutex.WaitOne(5000, false);
                if (hasHandle == false)
                    throw new TimeoutException("Timeout waiting for exclusive access");
            }
            catch (AbandonedMutexException)
            {
                // Log the fact that the mutex was abandoned in another process,
                // it will still get acquired
                hasHandle = true;
            }

            // Perform your work here.
        }
        finally
        {
            // edited by acidzombie24, added if statement
            if(hasHandle)
                mutex.ReleaseMutex();
        }
    }
}

Answer 2

使用接受的答案我创建了一个帮助器类，因此您可以像使用Lock语句一样使用它。只是想我会分享。

使用：

using (new SingleGlobalInstance(1000)) //1000ms timeout on global lock
{
    //Only 1 of these runs at a time
    RunSomeStuff();
}

辅助类：

class SingleGlobalInstance : IDisposable
{
    //edit by user "jitbit" - renamed private fields to "_"
    public bool _hasHandle = false;
    Mutex _mutex;

    private void InitMutex()
    {
        string appGuid = ((GuidAttribute)Assembly.GetExecutingAssembly().GetCustomAttributes(typeof(GuidAttribute), false).GetValue(0)).Value;
        string mutexId = string.Format("Global\\{{{0}}}", appGuid);
        _mutex = new Mutex(false, mutexId);

        var allowEveryoneRule = new MutexAccessRule(new SecurityIdentifier(WellKnownSidType.WorldSid, null), MutexRights.FullControl, AccessControlType.Allow);
        var securitySettings = new MutexSecurity();
        securitySettings.AddAccessRule(allowEveryoneRule);
        _mutex.SetAccessControl(securitySettings);
    }

    public SingleGlobalInstance(int timeOut)
    {
        InitMutex();
        try
        {
            if(timeOut < 0)
                _hasHandle = _mutex.WaitOne(Timeout.Infinite, false);
            else
                _hasHandle = _mutex.WaitOne(timeOut, false);

            if (_hasHandle == false)
                throw new TimeoutException("Timeout waiting for exclusive access on SingleInstance");
        }
        catch (AbandonedMutexException)
        {
            _hasHandle = true;
        }
    }


    public void Dispose()
    {
        if (_mutex != null)
        {
            if (_hasHandle)
                _mutex.ReleaseMutex();
            _mutex.Close();
        }
    }
}

Answer 3

如果另一个实例已在运行，此示例将在5秒后退出。

// unique id for global mutex - Global prefix means it is global to the machine
const string mutex_id = "Global\\{B1E7934A-F688-417f-8FCB-65C3985E9E27}";

static void Main(string[] args)
{

    using (var mutex = new Mutex(false, mutex_id))
    {
        try
        {
            try
            {
                if (!mutex.WaitOne(TimeSpan.FromSeconds(5), false))
                {
                    Console.WriteLine("Another instance of this program is running");
                    Environment.Exit(0);
                }
            }
            catch (AbandonedMutexException)
            {
                // Log the fact the mutex was abandoned in another process, it will still get aquired
            }

            // Perform your work here.
        }
        finally
        {
            mutex.ReleaseMutex();
        }
    }
}

Answer 4

当在2个不同用户下运行的2个进程同时尝试初始化互斥锁时，接受的答案中存在竞争条件。在第一个进程初始化互斥锁之后，如果第二个进程在第一个进程将访问规则设置为每个进程之前尝试初始化互斥锁，则第二个进程将抛出未经授权的异常。

请参阅下面的更正答案：

using System.Runtime.InteropServices;   //GuidAttribute
using System.Reflection;                //Assembly
using System.Threading;                 //Mutex
using System.Security.AccessControl;    //MutexAccessRule
using System.Security.Principal;        //SecurityIdentifier

static void Main(string[] args)
{
    // get application GUID as defined in AssemblyInfo.cs
    string appGuid = ((GuidAttribute)Assembly.GetExecutingAssembly().GetCustomAttributes(typeof(GuidAttribute), false).GetValue(0)).Value.ToString();

    // unique id for global mutex - Global prefix means it is global to the machine
    string mutexId = string.Format( "Global\\{{{0}}}", appGuid );

    bool createdNew;
        // edited by Jeremy Wiebe to add example of setting up security for multi-user usage
        // edited by 'Marc' to work also on localized systems (don't use just "Everyone") 
        var allowEveryoneRule = new MutexAccessRule(new SecurityIdentifier(WellKnownSidType.WorldSid, null), MutexRights.FullControl, AccessControlType.Allow);
        var securitySettings = new MutexSecurity();
        securitySettings.AddAccessRule(allowEveryoneRule);

        using (var mutex = new Mutex(false, mutexId, out createdNew, securitySettings))
        {

        // edited by acidzombie24
        var hasHandle = false;
        try
        {
            try
            {
                // note, you may want to time out here instead of waiting forever
                // edited by acidzombie24
                // mutex.WaitOne(Timeout.Infinite, false);
                hasHandle = mutex.WaitOne(5000, false);
                if (hasHandle == false)
                    throw new TimeoutException("Timeout waiting for exclusive access");
            }
            catch (AbandonedMutexException)
            {
                // Log the fact the mutex was abandoned in another process, it will still get aquired
                hasHandle = true;
            }

            // Perform your work here.
        }
        finally
        {
            // edited by acidzombie24, added if statemnet
            if(hasHandle)
                mutex.ReleaseMutex();
        }
    }
}

Answer 5

Mutex和WinApi CreateMutex（）都不适合我。

另一种解决方案：

static class Program
{
    [STAThread]
    static void Main()
    {
        if (SingleApplicationDetector.IsRunning()) {
            return;
        }

        Application.Run(new MainForm());

        SingleApplicationDetector.Close();
    }
}

SingleApplicationDetector：

using System;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Security.AccessControl;
using System.Threading;

public static class SingleApplicationDetector
{
    public static bool IsRunning()
    {
        string guid = ((GuidAttribute)Assembly.GetExecutingAssembly().GetCustomAttributes(typeof(GuidAttribute), false).GetValue(0)).Value.ToString();
        var semaphoreName = @"Global\" + guid;
        try {
            __semaphore = Semaphore.OpenExisting(semaphoreName, SemaphoreRights.Synchronize);

            Close();
            return true;
        }
        catch (Exception ex) {
            __semaphore = new Semaphore(0, 1, semaphoreName);
            return false;
        }
    }

    public static void Close()
    {
        if (__semaphore != null) {
            __semaphore.Close();
            __semaphore = null;
        }
    }

    private static Semaphore __semaphore;
}

使用信号量而不是互斥锁的原因：

Mutex类强制执行线程标识，因此互斥锁只能由获取它的线程释放。相比之下，Semaphore类不强制执行线程标识。

＆LT;＆LT; System.Threading.Mutex

参考：Semaphore.OpenExisting()

Answer 6

有时通过榜样学习最有帮助。在三个不同的控制台窗口中运行此控制台应用程序。您会看到，首先运行的应用程序首先获取了互斥锁，而其他两个正在等待轮换。然后在第一个应用程序中按Enter键，您将看到通过获取互斥锁现在可以继续运行应用程序2，但是应用程序3正在等待轮换。在应用程序2中按Enter键后，您将看到应用程序3继续。这说明了互斥锁的概念，该互斥锁保护一段代码仅由一个线程（在这种情况下为进程）执行，例如，写入文件为例。

using System;
using System.Threading;

namespace MutexExample
{
    class Program
    {
        static Mutex m = new Mutex(false, "myMutex");//create a new NAMED mutex, DO NOT OWN IT
        static void Main(string[] args)
        {
            Console.WriteLine("Waiting to acquire Mutex");
            m.WaitOne(); //ask to own the mutex, you'll be queued until it is released
            Console.WriteLine("Mutex acquired.\nPress enter to release Mutex");
            Console.ReadLine();
            m.ReleaseMutex();//release the mutex so other processes can use it
        }
    }
}

Answer 7

全局Mutex不仅用于确保仅具有一个应用程序实例。我个人更喜欢使用Microsoft.VisualBasic来确保像What is the correct way to create a single-instance WPF application?（Dale Ragan的回答）中所述的单实例应用程序……我发现将在新应用程序启动时收到的参数传递给初始的单实例应用程序更容易。

但是关于此线程中的某些先前代码，我希望每次不想对其进行锁定时都不要创建Mutex。对于单实例应用程序来说可能很好，但是在其他用法中，我觉得这有点过头了。

这就是为什么我建议此实现的原因：

用法：

static MutexGlobal _globalMutex = null;
static MutexGlobal GlobalMutexAccessEMTP
{
    get
    {
        if (_globalMutex == null)
        {
            _globalMutex = new MutexGlobal();
        }
        return _globalMutex;
    }
}

using (GlobalMutexAccessEMTP.GetAwaiter())
{
    ...
}

Mutex全球包装：

using System;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Security.AccessControl;
using System.Security.Principal;
using System.Threading;

namespace HQ.Util.General.Threading
{
    public class MutexGlobal : IDisposable
    {
        // ************************************************************************
        public string Name { get; private set; }
        internal Mutex Mutex { get; private set; }
        public int DefaultTimeOut { get; set; }
        public Func<int, bool> FuncTimeOutRetry { get; set; }

        // ************************************************************************
        public static MutexGlobal GetApplicationMutex(int defaultTimeOut = Timeout.Infinite)
        {
            return new MutexGlobal(defaultTimeOut, ((GuidAttribute)Assembly.GetExecutingAssembly().GetCustomAttributes(typeof(GuidAttribute), false).GetValue(0)).Value);
        }

        // ************************************************************************
        public MutexGlobal(int defaultTimeOut = Timeout.Infinite, string specificName = null)
        {
            try
            {
                if (string.IsNullOrEmpty(specificName))
                {
                    Name = Guid.NewGuid().ToString();
                }
                else
                {
                    Name = specificName;
                }

                Name = string.Format("Global\\{}", Name);

                DefaultTimeOut = defaultTimeOut;

                FuncTimeOutRetry = DefaultFuncTimeOutRetry;

                var allowEveryoneRule = new MutexAccessRule(new SecurityIdentifier(WellKnownSidType.WorldSid, null), MutexRights.FullControl, AccessControlType.Allow);
                var securitySettings = new MutexSecurity();
                securitySettings.AddAccessRule(allowEveryoneRule);

                Mutex = new Mutex(false, Name, out bool createdNew, securitySettings);

                if (Mutex == null)
                {
                    throw new Exception($"Unable to create mutex: {Name}");
                }
            }
            catch (Exception ex)
            {
                Log.Log.Instance.AddEntry(Log.LogType.LogException, $"Unable to create Mutex: {Name}", ex);
                throw;
            }
        }

        // ************************************************************************
        /// <summary>
        /// 
        /// </summary>
        /// <param name="timeOut"></param>
        /// <returns></returns>
        public MutexGlobalAwaiter GetAwaiter(int timeOut)
        {
            return new MutexGlobalAwaiter(this, timeOut);
        }

        // ************************************************************************
        /// <summary>
        /// 
        /// </summary>
        /// <param name="timeOut"></param>
        /// <returns></returns>
        public MutexGlobalAwaiter GetAwaiter()
        {
            return new MutexGlobalAwaiter(this, DefaultTimeOut);
        }

        // ************************************************************************
        /// <summary>
        /// This method could either throw any user specific exception or return 
        /// true to retry. Otherwise, retruning false will let the thread continue
        /// and you should verify the state of MutexGlobalAwaiter.HasTimedOut to 
        /// take proper action depending on timeout or not. 
        /// </summary>
        /// <param name="timeOutUsed"></param>
        /// <returns></returns>
        private bool DefaultFuncTimeOutRetry(int timeOutUsed)
        {
            // throw new TimeoutException($"Mutex {Name} timed out {timeOutUsed}.");

            Log.Log.Instance.AddEntry(Log.LogType.LogWarning, $"Mutex {Name} timeout: {timeOutUsed}.");
            return true; // retry
        }

        // ************************************************************************
        public void Dispose()
        {
            if (Mutex != null)
            {
                Mutex.ReleaseMutex();
                Mutex.Close();
            }
        }

        // ************************************************************************

    }
}

侍者

using System;

namespace HQ.Util.General.Threading
{
    public class MutexGlobalAwaiter : IDisposable
    {
        MutexGlobal _mutexGlobal = null;

        public bool HasTimedOut { get; set; } = false;

        internal MutexGlobalAwaiter(MutexGlobal mutexEx, int timeOut)
        {
            _mutexGlobal = mutexEx;

            do
            {
                HasTimedOut = !_mutexGlobal.Mutex.WaitOne(timeOut, false);
                if (! HasTimedOut) // Signal received
                {
                    return;
                }
            } while (_mutexGlobal.FuncTimeOutRetry(timeOut));
        }

        #region IDisposable Support
        private bool disposedValue = false; // To detect redundant calls

        protected virtual void Dispose(bool disposing)
        {
            if (!disposedValue)
            {
                if (disposing)
                {
                    _mutexGlobal.Mutex.ReleaseMutex();
                }

                // TODO: free unmanaged resources (unmanaged objects) and override a finalizer below.
                // TODO: set large fields to null.

                disposedValue = true;
            }
        }
        // TODO: override a finalizer only if Dispose(bool disposing) above has code to free unmanaged resources.
        // ~MutexExAwaiter()
        // {
        //   // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
        //   Dispose(false);
        // }

        // This code added to correctly implement the disposable pattern.
        public void Dispose()
        {
            // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
            Dispose(true);
            // TODO: uncomment the following line if the finalizer is overridden above.
            // GC.SuppressFinalize(this);
        }
        #endregion
    }
}

Answer 8

没有WaitOne的解决方案（用于WPF），因为它可能导致AbandonedMutexException。此解决方案使用Mutex构造函数，该构造函数返回createdNew布尔值，以检查是否已创建互斥体。它还使用GetType（）。GUID，因此重命名可执行文件不允许多个实例。

全局vs本地互斥锁，请参见： https://docs.microsoft.com/en-us/dotnet/api/system.threading.mutex?view=netframework-4.8

private Mutex mutex;
private bool mutexCreated;

public App()
{
    string mutexId = $"Global\\{GetType().GUID}";
    mutex = new Mutex(true, mutexId, out mutexCreated);
}

protected override void OnStartup(StartupEventArgs e)
{
    base.OnStartup(e);
    if (!mutexCreated)
    {
        MessageBox.Show("Already started!");
        Shutdown();
    }
}

由于Mutex实现IDisposable，因此它会自动释放，但出于完整性的考虑，请处置：

protected override void OnExit(ExitEventArgs e)
{
    base.OnExit(e);
    mutex.Dispose();
}

将所有内容移至基类，然后从接受的答案中添加allowEveryoneRule。还添加了ReleaseMutex，虽然看起来好像不是真正需要它，因为它是由操作系统自动释放的（如果应用程序崩溃并且从不调用ReleaseMutex，那您需要重新启动吗？）。

public class SingleApplication : Application
{
    private Mutex mutex;
    private bool mutexCreated;

    public SingleApplication()
    {
        string mutexId = $"Global\\{GetType().GUID}";

        MutexAccessRule allowEveryoneRule = new MutexAccessRule(
            new SecurityIdentifier(WellKnownSidType.WorldSid, null),
            MutexRights.FullControl, 
            AccessControlType.Allow);
        MutexSecurity securitySettings = new MutexSecurity();
        securitySettings.AddAccessRule(allowEveryoneRule);

        // initiallyOwned: true == false + mutex.WaitOne()
        mutex = new Mutex(initiallyOwned: true, mutexId, out mutexCreated, securitySettings);        }

    protected override void OnExit(ExitEventArgs e)
    {
        base.OnExit(e);
        if (mutexCreated)
        {
            try
            {
                mutex.ReleaseMutex();
            }
            catch (ApplicationException ex)
            {
                MessageBox.Show(ex.Message, ex.GetType().FullName, MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }
        mutex.Dispose();
    }

    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);
        if (!mutexCreated)
        {
            MessageBox.Show("Already started!");
            Shutdown();
        }
    }
}

在C＃中使用Global Mutex有什么好的模式？

8 个答案: