util/lock/ipc_lock.h

/* Copyright 2012, Google Inc.
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 * modification, are permitted provided that the following conditions are
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 *
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 *      notice, this list of conditions and the following disclaimer.
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 *      copyright notice, this list of conditions and the following
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 *      with the distribution.
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 *      from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 */

#ifndef __UTIL_IPC_LOCK_H
#define __UTIL_IPC_LOCK_H

struct ipc_lock {
	int is_held;	/* internal */
	char *filename;	/* provided by the developer */
	int fd;		/* internal */
};

/* don't use C99 initializers here, so this can be used in C++ code */
#define LOCKFILE_INIT(lockfile) \
	{ \
		0,		/* is_held */	\
		lockfile,	/* filename */	\
		-1,		/* fd */	\
	}

/*
 * acquire_lock: acquire a lock
 *
 * timeout <0 = no timeout (try forever)
 * timeout 0  = do not wait (return immediately)
 * timeout >0 = wait up to $timeout milliseconds (subject to kernel scheduling)
 *
 * return 0   = lock acquired
 * return >0  = lock was already held
 * return <0  = failed to acquire lock
 */
extern int acquire_lock(struct ipc_lock *lock, int timeout_msecs);

/*
 * release_lock: release a lock
 *
 * returns 0 if lock was released successfully
 * returns -1 if lock had not been held before the call
 */
extern int release_lock(struct ipc_lock *lock);

#endif /* __UTIL_IPC_LOCK_H */