Test and test-and-set: Difference between revisions

Revision as of 13:20, 28 September 2006

Revision as of 14:54, 9 November 2006

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To lower the overhead a more elaborate locking protocol ''Test and Test-and-set''

is used. The main idea is '''not''' to [[Busy waiting|spin]] in [[test-and-set]] but increase the likelihood of successful [[test-and-set]] by using following entry protocol to the lock:

''boolean'' locked := false ''// shared lock variable''

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}

The entry protocol uses normal memory reads to [[spin]], and waitwaiting for the lock to become free. [[Test-and-set]] is only used to try to get the lock when normal memory read says its free. Thus the expensive atomic memory operations happens less often than in simple spin around [[Test-and-set]].

If the [[programming language]] used supports [[Lazy evaluation#Minimal evaluation|minimal evaluation]], the entry protocol could be implemented as: