What is a good pattern for using a Global Mutex in C

Question

The Mutex class is very misunderstood  and Global mutexes even more so   What is good  safe pattern to use when creating Global mutexes   One that will work   Regardless of the locale my machine is in Is guaranteed to release the mutex properly Optionally does not hang forever if the mutex is not acquired Deals with cases where other processes abandon the mutex

User · Answer

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
        }
    }
}

User · Answer

Neither Mutex nor WinApi CreateMutex   works for me   An alternate solution   static class Program        STAThread      static void Main                 if  SingleApplicationDetector IsRunning                  return                     Application Run new MainForm              SingleApplicationDetector Close              And the 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      Reason to use Semaphore instead of Mutex      The Mutex class enforces thread identity  so a mutex can be released only by the thread that acquired it  By contrast  the Semaphore class does not enforce thread identity        lt  lt  System Threading Mutex   Ref  Semaphore OpenExisting

User · Answer

A solution  for WPF  without WaitOne because it can cause an AbandonedMutexException  This solution uses the Mutex constructor that returns the createdNew boolean to check if the mutex is already created  It also uses the GetType   GUID so renaming an executable doesn t allow multiple instances  Global vs local mutex see note in  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     quot Global   GetType   GUID  quot       mutex   new Mutex true  mutexId  out mutexCreated      protected override void OnStartup StartupEventArgs e        base OnStartup e       if   mutexCreated                MessageBox Show  quot Already started  quot            Shutdown             Because Mutex implements IDisposable it is released automatically but for completeness call dispose  protected override void OnExit ExitEventArgs e        base OnExit e       mutex Dispose       Move everything into a base class and add the allowEveryoneRule from the accepted answer  Also added ReleaseMutex though it doesn t look like it s really needed because it is released automatically by the OS  what if the application crashes and never calls ReleaseMutex would you need to reboot    public class SingleApplication   Application       private Mutex mutex      private bool mutexCreated       public SingleApplication                 string mutexId     quot Global   GetType   GUID  quot            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  quot Already started  quot                Shutdown

User · Answer

There is a race condition in the accepted answer when 2 processes running under 2 different users trying to initialize the mutex at the same time  After the first process initializes the mutex  if the second process tries to initialize the mutex before the first process sets the access rule to everyone  an unauthorized exception will be thrown by the second process   See below for corrected answer   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

User · Answer

A solution  for WPF  without WaitOne because it can cause an AbandonedMutexException  This solution uses the Mutex constructor that returns the createdNew boolean to check if the mutex is already created  It also uses the GetType   GUID so renaming an executable doesn t allow multiple instances  Global vs local mutex see note in  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     quot Global   GetType   GUID  quot       mutex   new Mutex true  mutexId  out mutexCreated      protected override void OnStartup StartupEventArgs e        base OnStartup e       if   mutexCreated                MessageBox Show  quot Already started  quot            Shutdown             Because Mutex implements IDisposable it is released automatically but for completeness call dispose  protected override void OnExit ExitEventArgs e        base OnExit e       mutex Dispose       Move everything into a base class and add the allowEveryoneRule from the accepted answer  Also added ReleaseMutex though it doesn t look like it s really needed because it is released automatically by the OS  what if the application crashes and never calls ReleaseMutex would you need to reboot    public class SingleApplication   Application       private Mutex mutex      private bool mutexCreated       public SingleApplication                 string mutexId     quot Global   GetType   GUID  quot            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  quot Already started  quot                Shutdown

User · Answer

This example will exit after 5 seconds if another instance is already running      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

User · Answer

I want to make sure this is out there  because it s so hard to get right   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

User · Answer

Using the accepted answer I create a helper class so you could use it in a similar way you would use the Lock statement  Just thought I d share    Use    using  new SingleGlobalInstance 1000     1000ms timeout on global lock         Only 1 of these runs at a time     RunSomeStuff        And the helper class   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  lt  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

User · Answer

I want to make sure this is out there  because it s so hard to get right   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

User · Answer

Using the accepted answer I create a helper class so you could use it in a similar way you would use the Lock statement  Just thought I d share    Use    using  new SingleGlobalInstance 1000     1000ms timeout on global lock         Only 1 of these runs at a time     RunSomeStuff        And the helper class   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  lt  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

User · Answer

I want to make sure this is out there  because it s so hard to get right   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

User · Answer

There is a race condition in the accepted answer when 2 processes running under 2 different users trying to initialize the mutex at the same time  After the first process initializes the mutex  if the second process tries to initialize the mutex before the first process sets the access rule to everyone  an unauthorized exception will be thrown by the second process   See below for corrected answer   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

User · Answer

A global Mutex is not only to ensure to have only one instance of an application  I personally prefer using Microsoft VisualBasic to ensure single instance application like described in What is the correct way to create a single-instance WPF application   Dale Ragan answer     I found that s easier to pass arguments received on new application startup to the initial single instance application   But regarding some previous code in this thread  I would prefer to not create a Mutex each time I want to have a lock on it  It could be fine for a single instance application but in other usage it appears to me has overkill   That s why I suggest this implementation instead   Usage   static MutexGlobal  globalMutex   null  static MutexGlobal GlobalMutexAccessEMTP       get               if   globalMutex    null                         globalMutex   new MutexGlobal                      return  globalMutex           using  GlobalMutexAccessEMTP GetAwaiter                     Mutex Global Wrapper   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 lt int  bool gt  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     0      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                                                                                                                            lt summary gt                            lt  summary gt               lt param name  timeOut  gt  lt  param gt               lt returns gt  lt  returns gt          public MutexGlobalAwaiter GetAwaiter int timeOut                        return new MutexGlobalAwaiter this  timeOut                                                                                                               lt summary gt                            lt  summary gt               lt param name  timeOut  gt  lt  param gt               lt returns gt  lt  returns gt          public MutexGlobalAwaiter GetAwaiter                         return new MutexGlobalAwaiter this  DefaultTimeOut                                                                                                               lt summary gt              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                lt  summary gt               lt param name  timeOutUsed  gt  lt  param gt               lt returns gt  lt  returns gt          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                                                                                                                            Awaiter  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

User · Answer

A global Mutex is not only to ensure to have only one instance of an application  I personally prefer using Microsoft VisualBasic to ensure single instance application like described in What is the correct way to create a single-instance WPF application   Dale Ragan answer     I found that s easier to pass arguments received on new application startup to the initial single instance application   But regarding some previous code in this thread  I would prefer to not create a Mutex each time I want to have a lock on it  It could be fine for a single instance application but in other usage it appears to me has overkill   That s why I suggest this implementation instead   Usage   static MutexGlobal  globalMutex   null  static MutexGlobal GlobalMutexAccessEMTP       get               if   globalMutex    null                         globalMutex   new MutexGlobal                      return  globalMutex           using  GlobalMutexAccessEMTP GetAwaiter                     Mutex Global Wrapper   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 lt int  bool gt  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     0      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                                                                                                                            lt summary gt                            lt  summary gt               lt param name  timeOut  gt  lt  param gt               lt returns gt  lt  returns gt          public MutexGlobalAwaiter GetAwaiter int timeOut                        return new MutexGlobalAwaiter this  timeOut                                                                                                               lt summary gt                            lt  summary gt               lt param name  timeOut  gt  lt  param gt               lt returns gt  lt  returns gt          public MutexGlobalAwaiter GetAwaiter                         return new MutexGlobalAwaiter this  DefaultTimeOut                                                                                                               lt summary gt              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                lt  summary gt               lt param name  timeOutUsed  gt  lt  param gt               lt returns gt  lt  returns gt          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                                                                                                                            Awaiter  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

User · Answer

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
        }
    }
}

User · Answer

Neither Mutex nor WinApi CreateMutex   works for me   An alternate solution   static class Program        STAThread      static void Main                 if  SingleApplicationDetector IsRunning                  return                     Application Run new MainForm              SingleApplicationDetector Close              And the 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      Reason to use Semaphore instead of Mutex      The Mutex class enforces thread identity  so a mutex can be released only by the thread that acquired it  By contrast  the Semaphore class does not enforce thread identity        lt  lt  System Threading Mutex   Ref  Semaphore OpenExisting

User · Answer

I want to make sure this is out there  because it s so hard to get right   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

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This example will exit after 5 seconds if another instance is already running      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

[c#] What is a good pattern for using a Global Mutex in C#?

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