peterson’s algorithm

Registers: Turn = 0 Want0 = 0 Want1 = 0

Process A

Want0 = 1;
Turn = 1;
while(Want1 && Turn == 1) {
  critical_section();
}
Want0 = 0;

Process B

Want1 = 1;
Turn = 0;
while(Want0 && Turn == 1) {
  critical_section();
}
Want1 = 0;

Disadvantage

  • busy waiting (spinning):

    The waiting process repeatedly tests the while-loop condition, rather than going into blocked state.

  • Low level implementation

    • Error-prone
    • Mutual exclusion needs to be simplified

  • Too specific to 2 processes.

Implementing this concretely

Implementing critical section

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