include/linux/call_once.h

Source file repositories/reference/linux-study-clean/include/linux/call_once.h

File Facts

System
Linux kernel
Corpus path
include/linux/call_once.h
Extension
.h
Size
1707 bytes
Lines
67
Domain
Core OS
Bucket
Core Kernel Interface
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

struct once {
        atomic_t state;
        struct mutex lock;
};

static inline void __once_init(struct once *once, const char *name,
			       struct lock_class_key *key)
{
        atomic_set(&once->state, ONCE_NOT_STARTED);
        __mutex_init(&once->lock, name, key);
}

#define once_init(once)							\
do {									\
	static struct lock_class_key __key;				\
	__once_init((once), #once, &__key);				\
} while (0)

/*
 * call_once - Ensure a function has been called exactly once
 *
 * @once: Tracking struct
 * @cb: Function to be called
 *
 * If @once has never completed successfully before, call @cb and, if
 * it returns a zero or positive value, mark @once as completed.  Return
 * the value returned by @cb
 *
 * If @once has completed successfully before, return 0.
 *
 * The call to @cb is implicitly surrounded by a mutex, though for
 * efficiency the * function avoids taking it after the first call.
 */
static inline int call_once(struct once *once, int (*cb)(struct once *))
{
	int r, state;

	/* Pairs with atomic_set_release() below.  */
	if (atomic_read_acquire(&once->state) == ONCE_COMPLETED)
		return 0;

	guard(mutex)(&once->lock);
	state = atomic_read(&once->state);
	if (unlikely(state != ONCE_NOT_STARTED))
		return WARN_ON_ONCE(state != ONCE_COMPLETED) ? -EINVAL : 0;

	atomic_set(&once->state, ONCE_RUNNING);
	r = cb(once);
	if (r < 0)
		atomic_set(&once->state, ONCE_NOT_STARTED);
	else
		atomic_set_release(&once->state, ONCE_COMPLETED);
	return r;
}

#endif /* _LINUX_CALL_ONCE_H */

Annotation

Implementation Notes