CPSC 3220 - DAY 9
SEPTEMBER 28, 2017

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Lock is initially free

Always acquire before accessing shared data structure at beginning.

Always release after finishing with shared data
	-End of procedure
	-Only the lock holder can release
	-Do not throw lock for someone else to release

Never access shared data without lock

Bounded Buffer
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For simplicity, assume no wraparound on the integers front and last
	-Front = total number of items that have ever been removed; tail = 
	total number of items ever inserted

Locks at beginning of procedure; unlock at end; no access of locks

Note that we don't know whether the buffer is still empty once we release the
lock - we only know the state of the buffer while holding the lock

Condition Variables

	-Waiting inside a critical section

	-Wait: atomically release lock and relinquish processor
		-Reacquire the lock when wakened

	-Signal: wake up a waiter, if any

	-Broadcast: wake up all waiters, if any.

	-Always hold locke when calling wait, signal, broadcast
		-Condition variable is sync FOR shared state
		-ALWAYS hold lock when accessing shared state

	-Condition variable is memoryless
		-If signal when no one is waiting no op
		-If wait before signal, waiter wakes up
	-Wait atomically releases lock