4. Other Hardware Primitives

Compare-and-swap:

  int CompareAndSwap(int *ptr, int expected, int new);

returns the old value and simultaneously updates to the new value if old == expected.

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Fetch-and-add:

  int FetchAndAdd(int *ptr);

returns the old value and simultaneously adds 1 and stores the new value.

Can be used to implement ticket lock and ensure fairness.