CreateEvent

The CreateEvent function creates a named or an unnamed event object.

HANDLE CreateEvent( 
LPSECURITY_ATTRIBUTES lpEventAttributes, 
BOOL bManualReset, 
BOOL bInitialState, 
LPTSTR lpName); 

Parameters

• lpEventAttributes
  Ignored. Must be NULL.

• bManualReset
  Boolean that specifies whether a manual-reset or auto-reset event object is created. If TRUE, then you must use the ResetEvent function to manually reset the state to nonsignaled. If FALSE, the system automatically resets the state to nonsignaled after a single waiting thread has been released.

• bInitialState
  Boolean that specifies the initial state of the event object. If TRUE, the initial state is signaled; otherwise, it is nonsignaled.

• lpName
  Pointer to a null-terminated string that specifies the name of the event object. The name is limited to MAX_PATH characters and can contain any character except the backslash path-separator character (\). Name comparison is case sensitive.

  If lpName matches the name of an existing named event object, the bManualReset and bInitialState parameters are ignored because they have already been set by the creating process.

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

  If lpName matches the name of 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 name space.

Return Values

A handle to the event object indicates success. 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. NULL indicates failure. To get extended error information, call GetLastError.

Remarks

The handle returned by CreateEvent has EVENT_ALL_ACCESS access to the new event object and can be used in any function that requires a handle to an event object.

Any thread of the calling process can specify the event-object handle in a call to one of the wait functions. The single-object wait functions return when the state of the specified object is signaled. The multiple-object wait functions can be instructed to return either when any one of the specified objects are signaled. When a wait function returns, the waiting thread is released to continue its execution.

The initial state of the event object is specified by the bInitialState parameter. Use the SetEvent function to set the state of an event object to signaled. Use the ResetEvent function to reset the state of an event object to nonsignaled.

When the state of a manual-reset event object is signaled, it remains signaled until it is explicitly reset to nonsignaled by the ResetEvent function. Any number of waiting threads, or threads that subsequently begin wait operations for the specified event object, can be released while the objects state is signaled.

When the state of an auto-reset event object is signaled, it remains signaled until a single waiting thread is released; the system then automatically resets the state to nonsignaled. If no threads are waiting, the event objects state remains signaled.

Multiple processes can have handles of the same event object, enabling use of the object for interprocess synchronization. The following object-sharing mechanism is available: a process can specify the name of an event object in a call to the CreateEvent function.

Use the CloseHandle function to close the handle. The system closes the handle automatically when the process terminates. The event object is destroyed when its last handle has been closed.

Requirements

Note   This API is part of the complete Windows CE OS package as provided by Microsoft. The functionality of a particular platform is determined by the original equipment manufacturer (OEM) and some devices may not support this API.

See Also

CloseHandle, ResetEvent, SetEvent, WaitForSingleObject

 Last updated on Tuesday, July 13, 2004

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