linux/include/linux/completion.h

#ifndef __LINUX_COMPLETION_H
#define __LINUX_COMPLETION_H

/*
 * (C) Copyright 2001 Linus Torvalds
 *
 * Atomic wait-for-completion handler data structures.
 * See kernel/sched.c for details.
 */

#include <linux/wait.h>

struct completion {
	unsigned int done;
	wait_queue_head_t wait;
};

#define COMPLETION_INITIALIZER(work) \
	{ 0, __WAIT_QUEUE_HEAD_INITIALIZER((work).wait) }

#define COMPLETION_INITIALIZER_ONSTACK(work) \
	({ init_completion(&work); work; })

#define DECLARE_COMPLETION(work) \
	struct completion work = COMPLETION_INITIALIZER(work)

/*
 * Lockdep needs to run a non-constant initializer for on-stack
 * completions - so we use the _ONSTACK() variant for those that
 * are on the kernel stack:
 */
#ifdef CONFIG_LOCKDEP
# define DECLARE_COMPLETION_ONSTACK(work) \
	struct completion work = COMPLETION_INITIALIZER_ONSTACK(work)
#else
# define DECLARE_COMPLETION_ONSTACK(work) DECLARE_COMPLETION(work)
#endif

static inline void init_completion(struct completion *x)
{
	x->done = 0;
	init_waitqueue_head(&x->wait);
}

extern void wait_for_completion(struct completion *);
extern int wait_for_completion_interruptible(struct completion *x);
extern int wait_for_completion_killable(struct completion *x);
extern unsigned long wait_for_completion_timeout(struct completion *x,
						   unsigned long timeout);
extern unsigned long wait_for_completion_interruptible_timeout(
			struct completion *x, unsigned long timeout);

extern void complete(struct completion *);
extern void complete_all(struct completion *);

#define INIT_COMPLETION(x)	((x).done = 0)


/**
 *	try_wait_for_completion - try to decrement a completion without blocking
 *	@x:	completion structure
 *
 *	Returns: 0 if a decrement cannot be done without blocking
 *		 1 if a decrement succeeded.
 *
 *	If a completion is being used as a counting completion,
 *	attempt to decrement the counter without blocking. This
 *	enables us to avoid waiting if the resource the completion
 *	is protecting is not available.
 */
static inline bool try_wait_for_completion(struct completion *x)
{
	int ret = 1;

	spin_lock_irq(&x->wait.lock);
	if (!x->done)
		ret = 0;
	else
		x->done--;
	spin_unlock_irq(&x->wait.lock);
	return ret;
}

/**
 *	completion_done - Test to see if a completion has any waiters
 *	@x:	completion structure
 *
 *	Returns: 0 if there are waiters (wait_for_completion() in progress)
 *		 1 if there are no waiters.
 *
 */
static inline bool completion_done(struct completion *x)
{
	int ret = 1;

	spin_lock_irq(&x->wait.lock);
	if (!x->done)
		ret = 0;
	spin_unlock_irq(&x->wait.lock);
	return ret;
}

#endif