lock.h

#ifndef __LOCK_H_
#define __LOCK_H_


#include <stdint.h>

/************
 *
 * Lock module provides tools for modules to share common resources (e.g. the SPI interface)
 *
 * NOTE: the lock routines are not interrupt-safe by default, they're meant to be used from within an event loop
 *
 */
 
/**
 * Opaque type to hold the state of a lock
 */
typedef struct _lock_t {
	const void *val;
} lock_t;


/**
 * Attempts to acquire given lock. 
 *
 * @param lock Pointer to the lock to attempt to acquire
 * @param a unique value representing the code attempting to acquire the lock. An
 *        easy way to have a guaranteed unique value is to use a pointer to a function
 *        or data structure in PROGMEM
 * @return True value if the lock was acquired successfully or has already been acquired by this module
 *         False if the lock is being held by another module
 *
 */
static inline uint8_t acquire_lock(volatile lock_t *lock, const void *value) {
  if(!lock->val) {
      return !!(lock->val = value);
  } else {
      return lock->val == value;
  }
}

/**
 * Checks to see if the module defined by lock_val holds the current lock
 *
 */
static inline uint8_t has_lock(volatile lock_t *lock, const void *lock_val) {
    return lock->val == lock_val;
}

/**
 * Unlocks the given lock
 *
 */
static inline void release_lock(volatile lock_t *lock) {
    lock->val = 0;
}

static inline const void *volatile lock_ptr(volatile lock_t *lock) {
	return lock->val;
}

#endif