XtAppMainLoop(3)

NAME

   XtAppNextEvent, XtAppPending, XtAppPeekEvent, XtAppProcessEvent,
   XtDispatchEvent, XtAppMainLoop - query and process events and input

SYNTAX

   void XtAppNextEvent(XtAppContext app_context, XEvent *event_return);

   Boolean XtAppPeekEvent(XtAppContext app_context, XEvent *event_return);

   XtInputMask XtAppPending(XtAppContext app_context);

   void XtAppProcessEvent(XtAppContext app_context, XtInputMask mask);

   Boolean XtDispatchEvent(XEvent *event);

   void XtAppMainLoop(XtAppContext app_context);

ARGUMENTS

   app_context
             Specifies the application context that identifies the
             application.

   event     Specifies a pointer to the event structure that is to be
             dispatched to the appropriate event handler.

   event_return
             Returns the event information to the specified event
             structure.

   mask      Specifies what types of events to process.  The mask is the
             bitwise inclusive OR of any combination of XtIMXEvent,
             XtIMTimer, XtIMAlternateInput, and XtIMSignal.  As a
             convenience, the X Toolkit defines the symbolic name XtIMAll
             to be the bitwise inclusive OR of all event types.

DESCRIPTION

   If the X event queue is empty, XtAppNextEvent flushes the X output
   buffers of each Display in the application context and waits for an
   event while looking at the other input sources, timeout timeout values,
   and signal handlers and calling any callback procedures triggered by
   them.  This wait time can be used for background processing (see
   Section 7.8).

   If there is an event in the queue, XtAppPeekEvent fills in the event
   and returns a nonzero value. If no X input is on the queue,
   XtAppPeekEvent flushes the output buffer and blocks until input is
   available (possibly calling some timeout callbacks in the process).  If
   the input is an event, XtAppPeekEvent fills in the event and returns a
   nonzero value.  Otherwise, the input is for an alternate input source,
   and XtAppPeekEvent returns zero.

   The XtAppPending function returns a nonzero value if there are events
   pending from the X server, timer pending, or other input sources
   pending. The value returned is a bit mask that is the OR of XtIMXEvent,
   XtIMTimer, XtIMAlternateInput, and XtIMSignal (see XtAppProcessEvent).
   If there are no events pending, XtAppPending flushes the output buffer
   and returns zero.

   The XtAppProcessEvent function processes one timer, alternate input,
   signal source, or X event.  If there is nothing of the appropriate type
   to process, XtAppProcessEvent blocks until there is.  If there is more
   than one type of thing available to process, it is undefined which will
   get processed.  Usually, this procedure is not called by client
   applications (see XtAppMainLoop).  XtAppProcessEvent processes timer
   events by calling any appropriate timer callbacks, alternate input by
   calling any appropriate alternate input callbacks, signal source by
   calling any appropriate signal callbacks, and X events by calling
   XtDispatchEvent.

   When an X event is received, it is passed to XtDispatchEvent, which
   calls the appropriate event handlers and passes them the widget, the
   event, and client-specific data registered with each procedure.  If
   there are no handlers for that event registered, the event is ignored
   and the dispatcher simply returns.  The order in which the handlers are
   called is undefined.

   The XtDispatchEvent function sends those events to the event handler
   functions that have been previously registered with the dispatch
   routine.  XtDispatchEvent returns True if it dispatched the event to
   some handler and False if it found no handler to dispatch the event to.
   The most common use of XtDispatchEvent is to dispatch events acquired
   with the XtAppNextEvent procedure.  However, it also can be used to
   dispatch user-constructed events.  XtDispatchEvent also is responsible
   for implementing the grab semantics for XtAddGrab.

   The XtAppMainLoop function first reads the next incoming X event by
   calling XtAppNextEvent and then it dispatches the event to the
   appropriate registered procedure by calling XtDispatchEvent.  This
   constitutes the main loop of X Toolkit applications, and, as such, it
   does not return unless XtAppSetExitFlag is called.  Applications are
   expected to exit in response to some user action.  There is nothing
   special about XtAppMainLoop; it is simply an loop that calls
   XtAppNextEvent and then XtDispatchEvent, until XtAppGetExitFlag()
   returns true.

   Applications can provide their own version of this loop, which tests
   some global termination flag or tests that the number of top-level
   widgets is larger than zero before circling back to the call to
   XtAppNextEvent.

SEE ALSO

   X Toolkit Intrinsics - C Language Interface
   Xlib - C Language X Interface

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