Hardware Solution - Test and Set

• Test and modify the content of a word atomically.

Function Test-and-Set( var target: boolean ) : boolean

begin

Test-and-Set := target;

target := true;

end

• Other variants exist.

Shared lock: boolean =false;

Repeat

while Test-and-Set(lock)

do no-op;

critical section

lock := false;

remainder section

Forever

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