xv6-riscv-kernel/kernel/spinlock.h

#pragma once

#include "types.h"

struct spinlock;

// spinlock.c

/**
 * Acquire the lock.
 * Loops (spins) until the lock is acquired.
 * Panics if the lock is already held by this cpu.
 */
void acquire(struct spinlock *);

/**
 * Check whether this cpu is holding the lock.
 * Interrupts must be off.
 */
int holding(struct spinlock *);

/**
 * Initialize spinlock
 */
void initlock(struct spinlock *, char *);

/**
 * Release the lock.
 * Panics if the lock is not held.
 */
void release(struct spinlock *);

/**
 * @brief push_off/pop_off are like intr_off()/intr_on() except that they are matched:
 * it takes two pop_off()s to undo two push_off()s.  Also, if interrupts
 * are initially off, then push_off, pop_off leaves them off.
 */
void push_off(void);

/** @copydoc pop_off */
void pop_off(void);

/** Mutual exclusion spin lock */
struct spinlock {
  u32 locked; // Is the lock held?

  // NOTE: Perhaps feature gate this?

  // For debugging:
  char       *name; // Name of lock.
  struct cpu *cpu;  // The cpu holding the lock.
};