CreateEvent

Description

Creates or opens a named or unnamed event object.

To specify an access mask for the object, use the CreateEventEx function.

Syntax

HANDLE WINAPI CreateEvent(
  _In_opt_ LPSECURITY_ATTRIBUTES lpEventAttributes,
  _In_     BOOL                  bManualReset,
  _In_     BOOL                  bInitialState,
  _In_opt_ LPCTSTR               lpName
);

Parameters

lpEventAttributes [in, optional]

A pointer to a SECURITY_ATTRIBUTES structure. If this parameter is NULL, the handle cannot be inherited by child processes.

The lpSecurityDescriptor member of the structure specifies a security descriptor for the new event. If lpEventAttributes is NULL, the event gets a default security descriptor. The ACLs in the default security descriptor for an event come from the primary or impersonation token of the creator.

bManualReset [in]

If this parameter is TRUE, the function creates a manual-reset event object, which requires the use of the ResetEvent function to set the event state to nonsignaled. If this parameter is FALSE, the function creates an auto-reset event object, and system automatically resets the event state to nonsignaled after a single waiting thread has been released.

bInitialState [in]

If this parameter is TRUE, the initial state of the event object is signaled; otherwise, it is nonsignaled.

lpName [in, optional]

The name of the event object. The name is limited to MAX_PATH characters. Name comparison is case sensitive.

If lpName matches the name of an existing named event object, this function requests the EVENT_ALL_ACCESS access right. In this case, the bManualReset and bInitialState parameters are ignored because they have already been set by the creating process. If the lpEventAttributes parameter is not NULL, it determines whether the handle can be inherited, but its security-descriptor member is ignored.

If lpName is NULL, the event object is created without a name.

If lpName matches the name of another kind of object in the same namespace (such as an existing semaphore, mutex, waitable timer, job, or file-mapping object), the function fails and the GetLastError function returns ERROR_INVALID_HANDLE. This occurs because these objects share the same namespace.

The name can have a "Global\" or "Local\" prefix to explicitly create the object in the global or session namespace. The remainder of the name can contain any character except the backslash character (\). Fast user switching is implemented using Terminal Services sessions. Kernel object names must follow the guidelines outlined for Terminal Services so that applications can support multiple users.

The object can be created in a private namespace.

Return value

If the function succeeds, the return value is a handle to the event object. If the named event object existed before the function call, the function returns a handle to the existing object and GetLastError returns ERROR_ALREADY_EXISTS.

If the function fails, the return value is NULL. To get extended error information, call GetLastError.