Explicit Posix/Notify() vs Guards

[Dale Stanbrough <dale@goanna.cs.rmit.EDU.AU>]

The Posix/Threads model (and Java) provide explicit notification schemes
for informing sleeping threads when to reevaluate any barrier conditions.
Ada provide guards on entries, and relies on the run time system to 
recognise when the condition associated with a guard _may_ have changed.

Clearly the Ada model may end up being overly conservative,
recalculating the barrier condition more often than is needed.
In some ways it may be less flexible in that other tasks may be
unable to cause reevaluation of the guards, in the same way
that an explicit notify would.

Is this a reasonable analysis, and what benefits are gained from
Ada's model?


Dale