Browse Prior Art Database

Inter-task Communication through File Access on MVS/ESA

IP.com Disclosure Number: IPCOM000110595D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 2 page(s) / 94K

Publishing Venue

IBM

Related People

Schmidt, DW: AUTHOR

Abstract

A program is disclosed that transparently captures application I/O requests on an MVS/ESA* platform and transforms those requests into a form of inter-task communication. The power in this redirection of both input and output files lies in the fact that it is done without the application's knowledge. The entire I/O capture process is established through JCL modifications.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Inter-task Communication through File Access on MVS/ESA

       A program is disclosed that transparently captures
application I/O requests on an MVS/ESA* platform and transforms those
requests into a form of inter-task communication.  The power in this
redirection of both input and output files lies in the fact that it
is done without the application's knowledge.  The entire I/O capture
process is established through JCL modifications.

      Since the MVS I/O capturing services provide the ability to
capture I/O requests to all programming languages, this concept could
easily be generalized such that all high-level language routines
could perform inter-task communication as if they were accessing
files.  No compiler changes would be required.  To complete the
package, a generalized inter-task communication facility, as
described in [*], could be used.

      The MVS I/O capturing services allow an MVS subsystem routine
to get control at the time an application opens/reads/writes to a
specific DDcard.  Once these routines get control, they can do
anything they want to satisfy the logical I/O request.  These
routines transparently gain control in place of the normal access
method routines that would be used to access disk files.
Conceptually, this MVS support allows subsystems to define their own
access methods.  This support is available to both files that are
allocated using JCL, and files that are dynamically allocated.  Part
of the service allows subsystem specific parameters to be specified
as part of the DDcard.  These parameters could be used to state
whether input or output is anticipated by the application, as
described in the following simplistic application flow.
     TSK1's JCL states that it wants read access to a logical file.
Upon first read, the application is blocked waiting for another task
to send data.
     At some point later, TSK2 opens a DDcard whose JCL requests a
connection to the TSK1 task.  The connection is automatically
established as part of the open processing.
     TSK2 could then write to that DDcard, causing TSK1's read(s) to
be satisfied.

      In the previous example, there was only one active connection
associated with each task.  However, t...