Computer Science 322
Operating Systems

Lecture 08: Cooperating Processes
Date: Wednesday, February 20, 2008

Announcements
- Class and office hours are likely to be cancelled on Friday.
- CPU Simulator still due Monday, writeup on Wednesday.
Cooperating Processes
- Bounded buffer problem
- Race conditions

The lecture assignment is postponed to Monday's lecture, to be due on Wednesday. There is no new lecture assignment due on Monday, February 25.

Bounded-Buffer Producer/Consumer leaving an empty slot:

Producer process

while (1) {
  ...
  produce item;
  ...
  while (((in+1)%n) == out); /* busy wait */
  buffer[in]=item;
  in=(in+1)%n;
}

Consumer process

while (1) {
  while (in==out); /* busy wait */
  item=buffer[out];
  out=(out+1)%n;
  ...
  consume item;
  ...
}

Bounded-Buffer Producer/Consumer using a shared counter:

Shared data

int buffer[n];
int in=0;
int out=0;
int counter=0;

Producer process

while (1) {
  ...
  produce item;
  ...
  while (counter==n); /* busy wait */
  buffer[in]=item;
  in=(in+1)%n;
  counter=counter+1;
}

Consumer process

while (1) {
  while (counter==0); /* busy wait */
  item=buffer[out];
  out=(out+1)%n;
  counter=counter-1;
  ...
  consume item;
  ...
}