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Monitor

Background

• OS semaphore

Model

• Hasen
• Hoare
• MESA

Issues

• Exclusion
• Synchronization

Solution

• Waiting Queue
  • Synchronizer
  • Condition Object

MESA wait

lock { // synchronized or lock.lock()
    while(!condition) {
        wait();
    }
}

• Why lock
  • ensure condition consistent
• Why while
  • condition may has been modified by other threads who holds the lock

When to notify()

• the same condition
• the same action
• need only one thread to wake up

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