Ping-Pong with One Semaphore?

void

PingPong() {

while(not done) {

Compute();

sem->V();
sem->P();

}

}

Nachos semaphores have Mesa-like semantics:

They do not guarantee that a waiting thread wakes up “in time” to consume the count added by a V().
- semaphores are not “fair”

- no count is “reserved” for a waking thread
- uses “passive” vs. “active” implementation

sem->Init(0);

blue: { sem->P(); PingPong(); }

purple: { PingPong(); }

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