Semaphore.TryOpenExisting Method

Definition

Opens a specified named semaphore, if it already exists, and returns a value that indicates whether the operation succeeded.

Overloads

TryOpenExisting(String, Semaphore)

Opens the specified named semaphore, if it already exists, and returns a value that indicates whether the operation succeeded.

TryOpenExisting(String, SemaphoreRights, Semaphore)

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

TryOpenExisting(String, Semaphore)

Opens the specified named semaphore, if it already exists, and returns a value that indicates whether the operation succeeded.

public:
 static bool TryOpenExisting(System::String ^ name, [Runtime::InteropServices::Out] System::Threading::Semaphore ^ % result);
public static bool TryOpenExisting (string name, out System.Threading.Semaphore result);
[System.Runtime.Versioning.SupportedOSPlatform("windows")]
public static bool TryOpenExisting (string name, out System.Threading.Semaphore? result);
public static bool TryOpenExisting (string name, out System.Threading.Semaphore? result);
static member TryOpenExisting : string * Semaphore -> bool
[<System.Runtime.Versioning.SupportedOSPlatform("windows")>]
static member TryOpenExisting : string * Semaphore -> bool
Public Shared Function TryOpenExisting (name As String, ByRef result As Semaphore) As Boolean

Parameters

name
String

The name of the synchronization object to be shared with other processes. The name is case-sensitive.

result
Semaphore

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

Returns

Boolean

true if the named semaphore was opened successfully; otherwise, false. In some cases, false may be returned for invalid names.

Attributes

Exceptions

name is an empty string.

-or-

.NET Framework only: name is longer than MAX_PATH (260 characters).

name is null.

name is invalid. This can be for various reasons, including some restrictions that may be placed by the operating system, such as an unknown prefix or invalid characters. Note that the name and common prefixes "Global" and "Local" are case-sensitive. For some invalid names, the method may return false instead.

-or-

There was some other error. The HResult property may provide more information.

The name is too long. Length restrictions may depend on the operating system or configuration.

The named semaphore exists, but the user does not have the security access required to use it.

Remarks

The name may be prefixed with Global\ or Local\ to specify a namespace. When the Global namespace is specified, the synchronization object may be shared with any processes on the system. When the Local namespace is specified, which is also the default when no namespace is specified, the synchronization object may be shared with processes in the same session. On Windows, a session is a login session, and services typically run in a different non-interactive session. On Unix-like operating systems, each shell has its own session. Session-local synchronization objects may be appropriate for synchronizing between processes with a parent/child relationship where they all run in the same session. For more information about synchornization object names on Windows, see Object Names.

If a synchronization object of the requested type exists in the namespace, the existing synchronization object is opened. If a synchronization object does not exist in the namespace, or a synchronization object of a different type exists in the namespace, false is returned.

To create the system semaphore when it does not already exist, use one of the Semaphore constructors that has a name parameter.

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

This method overload is equivalent to calling the TryOpenExisting method overload and specifying SemaphoreRights.Synchronize and SemaphoreRights.Modify rights, combined by using the bitwise OR operation. Specifying the SemaphoreRights.Synchronize flag allows a thread to enter the semaphore, and specifying the SemaphoreRights.Modify flag allows a thread to call the Release method.

Applies to

TryOpenExisting(String, SemaphoreRights, Semaphore)

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

public:
 static bool TryOpenExisting(System::String ^ name, System::Security::AccessControl::SemaphoreRights rights, [Runtime::InteropServices::Out] System::Threading::Semaphore ^ % result);
public static bool TryOpenExisting (string name, System.Security.AccessControl.SemaphoreRights rights, out System.Threading.Semaphore result);
static member TryOpenExisting : string * System.Security.AccessControl.SemaphoreRights * Semaphore -> bool
Public Shared Function TryOpenExisting (name As String, rights As SemaphoreRights, ByRef result As Semaphore) As Boolean

Parameters

name
String

The name of the synchronization object to be shared with other processes. The name is case-sensitive.

rights
SemaphoreRights

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

result
Semaphore

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

Returns

Boolean

true if the named semaphore was opened successfully; otherwise, false. In some cases, false may be returned for invalid names.

Exceptions

name is an empty string.

-or-

.NET Framework only: name is longer than MAX_PATH (260 characters).

name is null.

name is invalid. This can be for various reasons, including some restrictions that may be placed by the operating system, such as an unknown prefix or invalid characters. Note that the name and common prefixes "Global" and "Local" are case-sensitive. For some invalid names, the method may return false instead.

-or-

There was some other error. The HResult property may provide more information.

The name is too long. Length restrictions may depend on the operating system or configuration.

The named semaphore exists, but the user does not have the security access required to use it.

Remarks

The name may be prefixed with Global\ or Local\ to specify a namespace. When the Global namespace is specified, the synchronization object may be shared with any processes on the system. When the Local namespace is specified, which is also the default when no namespace is specified, the synchronization object may be shared with processes in the same session. On Windows, a session is a login session, and services typically run in a different non-interactive session. On Unix-like operating systems, each shell has its own session. Session-local synchronization objects may be appropriate for synchronizing between processes with a parent/child relationship where they all run in the same session. For more information about synchornization object names on Windows, see Object Names.

If a synchronization object of the requested type exists in the namespace, the existing synchronization object is opened. If a synchronization object does not exist in the namespace, or a synchronization object of a different type exists in the namespace, false is returned.

To create the system semaphore when it does not already exist, use one of the Semaphore constructors that has a name parameter.

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

The rights parameter must include the SemaphoreRights.Synchronize flag to allow threads to enter the semaphore, and the SemaphoreRights.Modify flag to allow threads to call the Release method.

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

Applies to