XtAppNextEvent(3Xt)X Version 11 (Release 6.6) XtAppNextEvent(3Xt)


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

     SYNTAX
          void XtAppNextEvent(app_context, event_return)
                XtAppContext app_context;
                XEvent *event_return;

          Boolean XtAppPeekEvent(app_context, event_return)
                XtAppContext app_context;
                XEvent *event_return;

          XtInputMask XtAppPending(app_context)
                XtAppContext app_context;

          void XtAppProcessEvent(app_context, mask)
                XtAppContext app_context;
                XtInputMask mask;

          Boolean XtDispatchEvent(event)
                XEvent *event;

          void XtAppMainLoop(app_context)
                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.
          Applications are expected to exit in response to some user
          action.  There is nothing special about XtAppMainLoop; it is
          simply an infinite loop that calls XtAppNextEvent and then
          XtDispatchEvent.

          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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