互斥锁类很容易被误解，而全局互斥锁更是如此。
在创建全局互斥对象时使用什么是好的、安全的模式?
一个会起作用的
不管我的机器在什么地方 是否保证正确释放互斥锁 如果没有获取互斥锁，则可选地不会永远挂起 处理其他进程放弃互斥锁的情况
当前回答
一个没有WaitOne的解决方案，因为它会导致一个AbandonedMutexException。 这个解决方案使用互斥量构造函数返回createdNew布尔值来检查互斥量是否已经创建。它还使用GetType()。GUID，因此重命名一个可执行文件不允许多个实例。
全局互斥与局部互斥参见: https://learn.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();
}
}
因为互斥锁实现了IDisposable，所以它被自动释放，但是为了完整性，调用dispose:
protected override void OnExit(ExitEventArgs e)
{
base.OnExit(e);
mutex.Dispose();
}
将所有内容移动到基类中，并从接受的答案中添加allowEveryoneRule。还添加了ReleaseMutex，虽然它看起来不像真的需要，因为它是由操作系统自动释放的(如果应用程序崩溃了，你需要重新启动ReleaseMutex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();
}
}
}
其他回答
Sometimes learning by example helps the most. Run this console application in three different console windows. You'll see that the application you ran first acquires the mutex first, while the other two are waiting their turn. Then press enter in the first application, you'll see that application 2 now continues running by acquiring the mutex, however application 3 is waiting its turn. After you press enter in application 2 you'll see that application 3 continues. This illustrates the concept of a mutex protecting a section of code to be executed only by one thread (in this case a process) like writing to a file as an example.
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
}
}
}
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();
}
}
和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类强制线程标识，因此只有获得互斥锁的线程才能释放它。相反，Semaphore类并不强制执行线程标识。 < < System.Threading.Mutex
裁判:Semaphore.OpenExisting ()
使用已接受的答案，我创建了一个帮助类，以便您可以以类似于使用Lock语句的方式使用它。只是想分享一下。
使用:
using (new SingleGlobalInstance(1000)) //1000ms timeout on global lock
{
//Only 1 of these runs at a time
RunSomeStuff();
}
helper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();
}
}
}
如果另一个实例已经在运行，则此示例将在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();
}
}
}
一个没有WaitOne的解决方案，因为它会导致一个AbandonedMutexException。 这个解决方案使用互斥量构造函数返回createdNew布尔值来检查互斥量是否已经创建。它还使用GetType()。GUID，因此重命名一个可执行文件不允许多个实例。
全局互斥与局部互斥参见: https://learn.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();
}
}
因为互斥锁实现了IDisposable，所以它被自动释放，但是为了完整性，调用dispose:
protected override void OnExit(ExitEventArgs e)
{
base.OnExit(e);
mutex.Dispose();
}
将所有内容移动到基类中，并从接受的答案中添加allowEveryoneRule。还添加了ReleaseMutex，虽然它看起来不像真的需要，因为它是由操作系统自动释放的(如果应用程序崩溃了，你需要重新启动ReleaseMutex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();
}
}
}
