SemaphoreAccessRule Class
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SemaphoreAccessRule Class

Represents a set of access rights allowed or denied for a user or group. This class cannot be inherited.

Namespace:  System.Security.AccessControl
Assembly:  System (in System.dll)

public ref class SemaphoreAccessRule sealed : public AccessRule

The SemaphoreAccessRule class is one of a set of classes that the .NET Framework provides for managing Windows access control security on named system semaphores. For an overview of these classes, and their relationship to the underlying Windows access control structures, see SemaphoreSecurity.


Windows access control security is meaningful only for named system semaphores. If a Semaphore object represents a local semaphore, access control is irrelevant.

To get a list of the rules currently applied to a named semaphore, use the Semaphore::GetAccessControl method to get a SemaphoreSecurity object, then use its GetAccessRules method to obtain a collection of SemaphoreAccessRule objects.

SemaphoreAccessRule objects do not map one-to-one with access control entries in the underlying discretionary access control list (DACL). When you get the set of all access rules for a semaphore, the set contains the minimum number of rules currently required to express all the access control entries.


The underlying access control entries change as you apply and remove rules. The information in rules is merged if possible, to maintain the smallest number of access control entries. Thus, when you read the current list of rules, it might not look exactly like the list of all the rules you have added.

Use SemaphoreAccessRule objects to specify access rights to allow or deny to a user or group. A SemaphoreAccessRule object always represents either allowed access or denied access, never both.

To apply a rule to a named system semaphore, use the Semaphore::GetAccessControl method to get the SemaphoreSecurity object. Modify the SemaphoreSecurity object by using its methods to add the rule, and then use the Semaphore::SetAccessControl method to reattach the security object.

Important noteImportant Note:

Changes you make to a SemaphoreSecurity object do not affect the access levels of the named semaphore until you call the Semaphore::SetAccessControl method to assign the altered security object to the named semaphore.

SemaphoreAccessRule objects are immutable. Security for a semaphore is modified using the methods of the SemaphoreSecurity class to add or remove rules; as you do this, the underlying access control entries are modified.


Security on synchronization objects is not supported for Windows 98 or Windows Millennium Edition.

The following code example demonstrates the separation between Allow rules and Deny rules, and shows the combination of rights in compatible rules. The example creates a SemaphoreSecurity object, adds rules that allow and deny various rights for the current user, and displays the resulting pair of rules. The example then allows new rights for the current user and displays the result, showing that the new rights are merged with the existing Allow rule.


This example does not attach the security object to a Semaphore object. Examples that attach security objects can be found in Semaphore::GetAccessControl and Semaphore::SetAccessControl.

No code example is currently available or this language may not be supported.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

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