CPU often provides atomic instructions for lock implementations. For example, x86s xchg instruction atomically exchanges the contents of two memory addresses. Implement a spin lock with this instruction, assuming xchg has been provided as a library function

// xchg sets the memory (addr) to newval, and returns the old value.

extern int xchg (int *addr, int newval);

struct spinlock { unsigned int locked;

};

{

}

void spinlock_release (struct spinlock *lock)

{

void spinlock_acquire (struct spinlock *lock)

}