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Synchronisation

If the task needs to output directly to the user's terminal, to switch it to `graphics' mode for example, it is necessary to ensure that the user-interface has completed output of previously sent text messages before the graphics output is sent. This is achieved by the user's code calling MSG_SYNC() which sends a MESSYS_SYNC message to the master task and waits for a MESSYS_SYNCREP message to be returned. As all messages are queued by the ADAM message system, we can be sure that all earlier message have been handled by the time the task receives the reply. Note that this only works where no other tasks can send messages to the user-interface in the meantime.

Where a control task lies between a subsidiary task and the user-interface, the messages are simply relayed.



next up previous 68
Next: Use of the TASK Library
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Previous: Re-scheduling

ADAM The Control Subsystem
Starlink System Note 77
A.J. Chipperfield
16 August 2001
E-mail:ussc@star.rl.ac.uk

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