NAME

initiate_request −  start request process without waiting for result

SYNOPSIS

C Syntax:

void initiate_request(fildes,class,ordinal,valid);
int fildes,class,ordinal,*valid;

FORTRAN77 Syntax:

subroutine initiate_request(fildes,class,ordinal,valid)
integer*4 fildes,class,ordinal,valid

Pascal Syntax:

procedure initiate_request(fildes,class,ordinal:integer;
var valid:integer);

DESCRIPTION

Input Parameters

fildes Integer file descriptor returned by gopen when an I/O path to a graphics device is opened. 

class One of the following device classes: LOCATOR or CHOICE.  The integer values assigned for these class designators are found in the Starbase include file used with your program. 

ordinal Logical device number ranging from 1 to the number of devices in this class. 

OUTPUT PARAMETER

valid If the device is not initialized or requests are not supported on a specific device, valid is set to FALSE (0).  Otherwise it is set to TRUE (1).  When Pascal is used, 0 and 1 are returned because TRUE and FALSE are reserved words in that programming language. 

DESCRIPTION

If the device is supported, initiate_request posts a request against it.  The request is completed when the device is triggered (in a device-dependent manner) or when the request is cancelled by receipt of a corresponding request_choice or request_locator that times out. 

A request can be performed on an input device while it is enabled for event generation.  The events-enabled mode is saved by the device and restored after the request has been executed. 

Request data is not sent to the event queue, but is placed instead in a separate virtual register.  Inquire_request_status can be used to determine whether any request data is present.  Request data can be read by using request_choice or request_locator (request_choice and request_locator do not require an earlier call to initiate_request before they can be used). 

Initiate_request provides a means for better utilizing devices that support asynchronous sampling during a pending request.  Thus, a program can initiate a request then continue other operations without waiting for its completion. 

SEE ALSO

inquire_request_status(3G), request_choice(3G), request_locator(3G). 
 

Hewlett-Packard Company  —  May 11, 2021