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- In computer science, the test-and-set CPU instruction is used to implement mutual exclusion in multiprocessor environments. Although a correct lock can be implemented with test-and-set, it can lead to resource contention in busy lock (caused by bus locking and cache invalidation when test-and-set operation needs to access memory atomically). To lower the overhead a more elaborate locking protocol test and test-and-set is used. Given a lock: boolean locked := false // shared lock variable Entry protocol is: procedure EnterCritical { do { while ( locked == true ) skip // spin until the lock seems free } while ( TestAndSet(locked) == true ) // attempt actual atomic locking using the test-and-set instruction} Exit protocol is: procedure ExitCritical { locked := false} The entry protocol uses normal memory reads to wait for the lock to become free. Test-and-set is only used to try to get the lock when normal memory read says it's free. Thus the expensive atomic memory operations happen less often than in a simple spin around test-and-set. If the programming language used supports short-circuit evaluation, the entry protocol could be implemented as: procedure EnterCritical { while ( locked == true or TestAndSet(locked) == true ) skip // spin until locked } (en)
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- 2527 (xsd:nonNegativeInteger)
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- In computer science, the test-and-set CPU instruction is used to implement mutual exclusion in multiprocessor environments. Although a correct lock can be implemented with test-and-set, it can lead to resource contention in busy lock (caused by bus locking and cache invalidation when test-and-set operation needs to access memory atomically). To lower the overhead a more elaborate locking protocol test and test-and-set is used. Given a lock: boolean locked := false // shared lock variable Entry protocol is: Exit protocol is: procedure ExitCritical { locked := false} (en)
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- Test and test-and-set (en)
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