Semaphore Constructor (Int32, Int32, String, Boolean, SemaphoreSecurity)
Initializes a new instance of the Semaphore class, specifying the maximum number of concurrent entries, optionally reserving some entries for the calling thread, optionally specifying the name of a system semaphore object, specifying a variable that receives a value indicating whether a new system semaphore was created, and specifying security access control for the system semaphore.
Assembly: System (in System.dll)
new : initialCount:int * maximumCount:int * name:string * createdNew:bool byref * semaphoreSecurity:SemaphoreSecurity -> Semaphore
- Type: System.Int32
The initial number of requests for the semaphore that can be satisfied concurrently.
- Type: System.Int32
The maximum number of requests for the semaphore that can be satisfied concurrently.
- Type: System.String
The name of a named system semaphore object.
- Type: System.Boolean
When this method returns, contains true if a local semaphore was created (that is, if name is a null reference (Nothing in Visual Basic) or an empty string) or if the specified named system semaphore was created; false if the specified named system semaphore already existed. This parameter is passed uninitialized.
initialCount is greater than maximumCount.
name is longer than 260 characters.
maximumCount is less than 1.
initialCount is less than 0.
The named semaphore exists and has access control security, and the user does not have SemaphoreRights.FullControl.
A Win32 error occurred.
The named semaphore cannot be created, perhaps because a wait handle of a different type has the same name.
Use this constructor to apply access control security to a named system semaphore when it is created, preventing other code from taking control of the semaphore.
If the named system semaphore does not exist, it is created with the specified access control security. If the named semaphore exists, the specified access control security is ignored.
The caller has full control over the newly created Semaphore object even if semaphoreSecurity denies or fails to grant some access rights to the current user. However, if the current user attempts to get another Semaphore object to represent the same named semaphore, using either a constructor or the OpenExisting method, Windows access control security is applied.
If the named system semaphore does not exist, it is created with the initial count and maximum count specified by initialCount and maximumCount. If the named system semaphore already exists, initialCount and maximumCount are not used, although invalid values still cause exceptions. Use the createdNew parameter to determine whether the system semaphore was created by this constructor.
If initialCount is less than maximumCount, and createdNew is true, the effect is the same as if the current thread had called WaitOne (maximumCount minus initialCount) times.
If you specify a null reference (Nothing in Visual Basic) or an empty string for name, a local semaphore is created, as if you had called the Semaphore(Int32, Int32) constructor overload. In this case, createdNew is always true.
Because named semaphores are visible throughout the operating system, they can be used to coordinate resource use across process boundaries.
The following code example demonstrates the cross-process behavior of a named semaphore with access control security. The example uses the OpenExisting(String) method overload to test for the existence of a named semaphore. If the semaphore does not exist, it is created with a maximum count of two and with access control security that denies the current user the right to use the semaphore but grants the right to read and change permissions on the semaphore. If you run the compiled example from two command windows, the second copy will throw an access violation exception on the call to the OpenExisting(String) method. The exception is caught, and the example uses the OpenExisting(String, SemaphoreRights) method overload to open the semaphore with the rights needed to read and change the permissions.
After the permissions are changed, the semaphore is opened with the rights required to enter and release. If you run the compiled example from a third command window, it runs using the new permissions.
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.