Semaphore Implementation

• Semaphore is a record:

type semaphore = record

value: integer;

L : list of process;

end;

• Assumes two operations:

  • block suspends the process that invokes it.
  • Wakeup(p) resumes the execution of a blocked process p.

Atomic operations:

• Wait(s):

S.value := S.value -1;

if S.value < 0

add this process to S.L;

block;

end;

• Signal(s):

S.value := S.value + 1;

if S.value ? 0

remove a process P from S.L;

wakeup(P);

end;

Previous slide

Next slide

Back to first slide

View graphic version