The philosophy used in providing asynchronous input is to allow the Application Program to issue an asynchronous input request (normally coupled to the display of an menu), and to then poll for the detection of input. Once this is detected, the input line may be scanned as normal. By default only the Menu Display Subprograms and the Verb Input Subprogram may be used asynchronously, but UIPACK may be put into a mode whereby all prompted input Subprograms may be used asynchronously. Asynchronous Input is performed by the Application Program requesting asynchronous input mode (via a call to UI_INPUT_MODE, described in a later Section) and then calling the required Menu Display or Prompted Input Subprogram repeatedly until successful input is signalled. Alternatively the Input request may be initiated by calling the appropriate subprogram and then the input status may be polled by using Subprogram UI_TEST_INPUT. The original subprogram should then be recalled in order to act on the input and proceed. For VAX/VMS Systems an Application Programmer may define a Subroutine to be called automatically from the AST Handler associated with Asynchronous Input. This would allow, for example, the appropriate DAQ Package (CDF-166) Subprograms to be called to cancel outstanding ``Get Event" or ``Get Space" requests.
This Feature only implemented
for VAX/VMS Systems in Text Mode