HandlerRoutine info  Overview  Group

A HandlerRoutine function is a function that a console process specifies to handle control signals received by the process. The function can have any name.

BOOL HandlerRoutine(

DWORD dwCtrlType	// control signal type
);

Parameters

dwCtrlType

Indicates the type of control signal received by the handler. This value is one of the following:

Signal	Description
CTRL_C_EVENT	A CTRL+C signal was received, either from keyboard input or from a signal generated by the GenerateConsoleCtrlEvent function.
CTRL_BREAK_EVENT	A CTRL+BREAK signal was received, either from keyboard input or from a signal generated by GenerateConsoleCtrlEvent.
CTRL_CLOSE_EVENT	A signal that the system sends to all processes attached to a console when the user closes the console (either by choosing the Close command from the console window’s System menu, or by choosing the End Task command from the Task List).
CTRL_LOGOFF_EVENT	A signal that the system sends to all console processes when a user is logging off. This signal does not indicate which user is logging off, so no assumptions can be made.
CTRL_SHUTDOWN_EVENT	A signal that the system sends to all console processes when the system is shutting down.

Return Values

If the function handles the control signal, it should return TRUE. If it returns FALSE, the next handler function in the list of handlers for this process is used.

Remarks

Each console process has its own list of HandlerRoutine functions. Initially, this list contains only a default handler function that calls ExitProcess. A console process adds or removes additional handler functions by calling the SetConsoleCtrlHandler function, which does not affect the list of handler functions for other processes. When a console process receives any of the control signals, its handler functions are called on a last-registered, first-called basis until one of the handlers returns TRUE. If none of the handlers returns TRUE, the default handler is called.

The CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT, and CTRL_SHUTDOWN_EVENT signals give the process an opportunity to clean up before termination. A HandlerRoutine called to handle any of these signals can do one of the following after performing any cleanup operations:

• Call the ExitProcess function to terminate the process.

• Return FALSE. If none of the registered handler functions returns TRUE, the default handler terminates the process.

• Return TRUE. In this case, no other handler functions are called, and the system displays a pop-up dialog box that asks the user whether to terminate the process. The system also displays the dialog box if the process does not respond within a certain time-out period (5 seconds for CTRL_CLOSE_EVENT, and 20 seconds for CTRL_LOGOFF_EVENT and CTRL_SHUTDOWN_EVENT).

A process can use the SetProcessShutdownParameters function to prevent the CTRL_LOGOFF_EVENT and CTRL_SHUTDOWN_EVENT dialog box from being displayed. In this case, the system just terminates the process when a HandlerRoutine returns TRUE or when the time-out period elapses.

See Also

ExitProcess, GenerateConsoleCtrlEvent, GetProcessShutdownParameters, SetConsoleCtrlHandler, SetProcessShutdownParameters