Busy Waiting with Test-and-Set

• A test-and-set instruction provides the atomic guarantees needed to implement critical sections

Boolean Function test-and-set (var target: boolean)

begin

test-and-set := target ; return old value of target

target := true ; set target to true

end

using test-and-set(initialize aLock:= false at beginning)

while test-and-set(aLock)do no-op ; spin until lock is free (and atomically

; acquire the lock)

<do the critical section>

aLock := false ; free the lock for someone else

Previous slide

Back to first slide

View graphic version