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/* $Id: liblock.h,v 1.4 2000/04/26 22:31:10 mrsam Exp $ */

#ifndef liblock_h
#define liblock_h

** Copyright 1998 - 1999 Double Precision, Inc.  See COPYING for
** distribution information.

#ifdef      __cplusplus
extern "C" {

#include    <sys/types.h>

#include    "config.h"

#define     ll_whence_start   0
#define     ll_whence_curpos 1
#define     ll_whence_end 2

#define     ll_readlock 0
#define     ll_writelock      4
#define     ll_unlock   8
#define     ll_wait           16

int   ll_lockfd(int,    /* File descriptor */
            int,  /* ll_ bitmask */
            LL_OFFSET_TYPE,   /* Start */
            LL_OFFSET_TYPE);  /* Length */

/* Some useful macros: ll_lock_ex - exclusive lock on a file,
            ll_lock_ex_test - attempt an exclusive lock on a file
            ll_unlock_ex - unlock a file

#define     ll_lock_ex(f)     \
      ll_lockfd( (f), ll_writelock|ll_whence_start|ll_wait, 0, 0)

#define     ll_lock_ex_test(f)      \
      ll_lockfd( (f), ll_writelock|ll_whence_start, 0, 0)

#define     ll_unlock_ex(f)   \
      ll_lockfd( (f), ll_unlock|ll_whence_start, 0, 0)

** Value-added: functions that reliably start and stop a daemon process,
** permitting only one daemon process running.  Utilizes a lock file, and a
** pidfile.

int ll_daemon_start(const char *lockfile);
void ll_daemon_started(const char *pidfile, int fd);
int ll_daemon_resetio();
int ll_daemon_stop(const char *lockfile, const char *pidfile);
int ll_daemon_restart(const char *lockfile, const char *pidfile);

  The basic scenario

    if ((fd=ll_daemon_start(lockfilename)) < 0)
           error();  exit(1);

    ... Some custom initialization here ...

    ll_daemon_started(pidfile, fd);

    ll_daemon_resetio();   ... this one is optional

To stop this daemon:

ll_daemon_stop (lockfilename, pidfile)

ll_daemon_start attempts to start a daemon process going.  It does only
a partial setup.  If it detects that the daemon process is already
running, it itself does an exit(0), not returning to the parent.

If there was a failure starting a daemon process, -1 is return, else
we return a transparent file descriptor, which will have to be passed as
the secodn argument to ll_daemon_started().

When ll_daemon_start returns, we're already running in a partially set-up
daemon process.  The setup isn't complete just yet.  The parent function
can perform any other custom initialization.  If initialization fails,
the parent function can simply exit.  Otherwise, if the initialization
completes, ll_daemon_started must be called in order to save this daemon
process's pid in the pid file (2nd arg must be the return from ll_daemon_start.

To stop a daemon process, simply call ll_daemon_stop.  Nothing too
sophisticated here.

To send the daemon process a SIGHUP, call ll_daemon_restart.

#ifdef      __cplusplus
} ;


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