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Shared Memory Synchronization

Semaphore s = INIT(1)
P1: loop     P2: loop
      P(s)         P(s)
      C1           C2
      V(s)         V(s)

• Counter variable holding natural number.
• Atomic operations $P$ and $V$.
• $P(s)$: if $s>0$ then else block.
• $V(s)$: if processes blocked on $s$ then release some process else .