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Transactions

AMS communications are carried out as a series of `transactions'. A transaction consists of an initial message and a number of further messages (replies) in either direction, associated with the initial message. Separate transactions are used to set up a communications path and to carry out the business of obeying a command. A command transaction is started by calling ams_send and is terminated as described under `Getting Expected Replies'.

When sending a message, the user specifies a message_function and a message_status which are passed as arguments to functions ams_send or ams_reply.

The value of message_function may be:

MESSYS__INIT
Used to ask for a communications link to another task. (ams_send only)1.
MESSYS__DE_INIT
Used to close a communications link to another task.
MESSYS__MESSAGE
Used for all other purposes and qualified by the message_status and possibly other arguments.



next up previous 199
Next: Task Initialisation
Up: AMS The Unix ADAM Message System
Previous: Introduction

AMS The Unix ADAM Message System
Starlink User Note 241
B D Kelly (ROE)
A J Chipperfield (RAL)
16 August 2001
E-mail:ussc@star.rl.ac.uk

Copyright © 2000 Council for the Central Laboratory of the Research Councils