Browse Prior Art Database

Event Signalling to Multiple Processes

IP.com Disclosure Number: IPCOM000014693D
Original Publication Date: 1999-Dec-01
Included in the Prior Art Database: 2003-Jun-20
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Geoffrey Winn: AUTHOR [+2]

Abstract

This invention solves the problem of efficiently notifying a set of processes of the occurence of an event, where the membership of the set is not known to the entity signalling the event. The solution is applicable to the OpenVMS* operating system. The invention uses OpenVMS mailboxes and write-attention (WRTATTN) ASTs. A mailbox is a pseudo-device, normally used for OpenVMS processes to exchange data. A write attention AST is effectively a process-private interrupt. A process with an interest in a mailbox can declare that a named procedure within the process (referred to as an AST routine) is to be run when data is written to the mailbox. The process then continues executing, without having to poll the mailbox or otherwise stall, knowing that the AST routine will execute when data is available in the mailbox. The normal use of this mechanism is for one process to write data into a mailbox and another to read from it, prompted to do so by the AST mechanism. The mailbox then functions as a buffer.

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Event Signalling to Multiple Processes

This invention solves the problem of efficiently notifying a set of processes
of the occurence of an event, where the membership of the set is not known to
the entity signalling the event. The solution is applicable to the OpenVMS*
operating system.

      The invention uses OpenVMS mailboxes and
write-attention (WRTATTN) ASTs.

      - A mailbox is a pseudo-device, normally used
for OpenVMS processes to exchange data.

      - A write attention AST is effectively a
process-private interrupt. A process with an
interest in a mailbox can declare that a named
procedure within the process (referred to as an AST
routine) is to be run when data is written to the
mailbox. The process then continues executing,
without having to poll the mailbox or otherwise
stall, knowing that the AST routine will execute
when data is available in the mailbox. The normal
use of this mechanism is for one process to write
data into a mailbox and another to read from it,
prompted to do so by the AST mechanism. The mailbox
then functions as a buffer.

      This invention uses the mailbox and AST
mechanism for multi-process synchronisation rather
than data exchange. A mailbox is created for each
event. Every process that is interested in a
particular event declares a write attention AST for
the corresponding mailbox. When a process wishes to
signal an event, it writes a single byte to the
appropriate mailbox. (The value of the byte is
unimportant.) This write triggers the AST routines
of all the registered processes, effectively
notifying them of the event. Since the byte remains
in the mailbox until it is read, even a process
which requests a write attention AST after the
write has ha...