EventWaitHandle::TryOpenExisting Method (String^, EventWaitHandleRights, EventWaitHandle^%)

.NET Framework (current version)

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Opens the specified named synchronization event, if it already exists, with the desired security access, and returns a value that indicates whether the operation succeeded.

Namespace:   System.Threading
Assembly:  mscorlib (in mscorlib.dll)

static bool TryOpenExisting(
	String^ name,
	EventWaitHandleRights rights,
	[OutAttribute] EventWaitHandle^% result


Type: System::String^

The name of the system synchronization event to open.

Type: System.Security.AccessControl::EventWaitHandleRights

A bitwise combination of the enumeration values that represent the desired security access.

Type: System.Threading::EventWaitHandle^%

When this method returns, contains a EventWaitHandle object that represents the named synchronization event if the call succeeded, or null if the call failed. This parameter is treated as uninitialized.

Return Value

Type: System::Boolean

true if the named synchronization event was opened successfully; otherwise, false.

Exception Condition

name is an empty string.


name is longer than 260 characters.


name is null.


A Win32 error occurred.


The named event exists, but the user does not have the desired security access.

If the named synchronization event does not exist, this method does not create it. To create the system event when it does not already exist, use one of the EventWaitHandle constructors that has a name parameter.

If you are uncertain whether a named synchronization event exists, use this method overload instead of the OpenExisting(String^, EventWaitHandleRights) method overload, which throws an exception if the synchronization event does not exist.

The rights parameter must include the EventWaitHandleRights::Synchronize flag to allow threads to wait on the event, and the EventWaitHandleRights::Modify flag to allow threads to call the Set and Reset methods.

Multiple calls to this method that use the same value for name do not necessarily return the same EventWaitHandle object, even though the objects that are returned represent the same named system event.


requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.

.NET Framework
Available since 4.5
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