Bounded buffer problem

producer consumer problem

issues

no data in buffe: consumer has nothing to consume: data race
buffer is full: no space for producer to produce: busy waiting

private vars

in: next pos in buf to be writted
out: next pos in buf to be read

shared variables

buffer
counter: number of items in buffer

waiting

busy: proces keeps checking (if buffer is still full) wasting CPU time
non busy: suspend the process

soution with shared array

PRODUCER: repeat 
		...
		produce an item in nextp 
		...
		while counter = n do no-op;
		buffer[in] := nextp;
		in := in+1 mod n;
		counter := counter+1;
	until false;	
CONSUMER: repeat 
		while counter = 0 do no-op;
		nextc := buffer[out];
		out := out+1 mod n;
		counter := counter-1;

		...
		consume the item in nextc 
		...
	until false;

counter is a shared variable - causes a data race problem

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Bounded buffer problem

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