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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: Use of the TASK Library
Up: ADAM The Control Subsystem
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