Mutex Constructor (Boolean, String, Boolean, MutexSecurity)
Initializes a new instance of the Mutex class with a Boolean value that indicates whether the calling thread should have initial ownership of the mutex, a string that is the name of the mutex, a Boolean variable that, when the method returns, indicates whether the calling thread was granted initial ownership of the mutex, and the access control security to be applied to the named mutex.
Assembly: mscorlib (in mscorlib.dll)
new : initiallyOwned:bool * name:string * createdNew:bool byref * mutexSecurity:MutexSecurity -> Mutex
- Type: System.Boolean
true to give the calling thread initial ownership of the named system mutex if the named system mutex is created as a result of this call; otherwise, false.
- Type: System.String
The name of the system mutex. If the value is a null reference (Nothing in Visual Basic), the Mutex is unnamed.
- Type: System.Boolean
When this method returns, contains a Boolean that is true if a local mutex was created (that is, if name is a null reference (Nothing in Visual Basic) or an empty string) or if the specified named system mutex was created; false if the specified named system mutex already existed. This parameter is passed uninitialized.
A Win32 error occurred.
The named mutex exists and has access control security, but the user does not have MutexRights.FullControl.
The named mutex cannot be created, perhaps because a wait handle of a different type has the same name.
name is longer than 260 characters.
If name is not a null reference (Nothing in Visual Basic) and initiallyOwned is true, the calling thread owns the named mutex only if createdNew is true after the call. Otherwise the thread can request the mutex by calling the WaitOne method.
Use this constructor to apply access control security to a named system mutex when it is created, preventing other code from taking control of the mutex.
If the named system mutex does not exist, it is created with the specified access control security. If the named mutex exists, the specified access control security is ignored.
The caller has full control over the newly created Mutex object even if mutexSecurity denies or fails to grant some access rights to the current user. However, if the current user attempts to get another Mutex object to represent the same named mutex, using either a constructor or the OpenExisting method, Windows access control security is applied.
If the named mutex has already been created with access control security, and the caller does not have MutexRights.FullControl, an exception is thrown. To open an existing named mutex with only those permissions needed for synchronizing thread activities, see the OpenExisting method.
If you specify a null reference (Nothing in Visual Basic) or an empty string for name, a local mutex is created, as if you had called the Mutex(Boolean) constructor. In this case, createdNew is always true.
Because they are system-wide, named mutexes can be used to coordinate resource use across process boundaries.
On a server that is running Terminal Services, a named system mutex can have two levels of visibility. If its name begins with the prefix "Global\", the mutex is visible in all terminal server sessions. If its name begins with the prefix "Local\", the mutex is visible only in the terminal server session where it was created. In that case, a separate mutex with the same name can exist in each of the other terminal server sessions on the server. If you do not specify a prefix when you create a named mutex, it takes the prefix "Local\". Within a terminal server session, two mutexes whose names differ only by their prefixes are separate mutexes, and both are visible to all processes in the terminal server session. That is, the prefix names "Global\" and "Local\" describe the scope of the mutex name relative to terminal server sessions, not relative to processes.
The following code example demonstrates the cross-process behavior of a named mutex with access control security. The example uses the OpenExisting(String) method overload to test for the existence of a named mutex.
If the mutex does not exist, it is created with initial ownership and access control security that denies the current user the right to use the mutex, but grants the right to read and change permissions on the mutex.
If you run the compiled example from two command windows, the second copy will throw an access violation exception on the call to OpenExisting(String). The exception is caught, and the example uses the OpenExisting(String, MutexRights) method overload to open the mutex with the rights needed to read and change the permissions.
After the permissions are changed, the mutex is opened with the rights required to enter and release it. If you run the compiled example from a third command window, it runs using the new permissions.
Requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.