libs/liblock/liblock.h

   1
   2 #ifndef liblock_h
   3 #define liblock_h
   4
   5 /*
   6 ** Copyright 1998 - 1999 Double Precision, Inc.  See COPYING for
   7 ** distribution information.
   8 */
   9
  10 #ifdef  __cplusplus
  11 extern "C" {
  12 #endif
  13
  14 #if     HAVE_CONFIG_H
  15 #include        "liblock/config.h"
  16 #endif
  17 #include        <sys/types.h>
  18
  19 #define ll_whence_start 0
  20 #define ll_whence_curpos 1
  21 #define ll_whence_end 2
  22
  23 #define ll_readlock     0
  24 #define ll_writelock    4
  25 #define ll_unlock       8
  26 #define ll_wait         16
  27
  28 int     ll_lockfd(int,  /* File descriptor */
  29                 int,    /* ll_ bitmask */
  30                 LL_OFFSET_TYPE, /* Start */
  31                 LL_OFFSET_TYPE);        /* Length */
  32
  33
  34 /* Some useful macros: ll_lock_ex - exclusive lock on a file,
  35                 ll_lock_ex_test - attempt an exclusive lock on a file
  36                 ll_unlock_ex - unlock a file
  37 */
  38
  39 #define ll_lock_ex(f)   \
  40         ll_lockfd( (f), ll_writelock|ll_whence_start|ll_wait, 0, 0)
  41
  42 #define ll_lock_ex_test(f)      \
  43         ll_lockfd( (f), ll_writelock|ll_whence_start, 0, 0)
  44
  45 #define ll_unlock_ex(f) \
  46         ll_lockfd( (f), ll_unlock|ll_whence_start, 0, 0)
  47
  48
  49 /*
  50 ** Value-added: functions that reliably start and stop a daemon process,
  51 ** permitting only one daemon process running.  Utilizes a lock file, and a
  52 ** pidfile.
  53 */
  54
  55 int ll_daemon_start(const char *lockfile);
  56 void ll_daemon_started(const char *pidfile, int fd);
  57 int ll_daemon_resetio();
  58 int ll_daemon_stop(const char *lockfile, const char *pidfile);
  59 int ll_daemon_restart(const char *lockfile, const char *pidfile);
  60
  61 /*
  62   The basic scenario
  63
  64 main()
  65 {
  66     if ((fd=ll_daemon_start(lockfilename)) < 0)
  67     {
  68            error();  exit(1);
  69     }
  70
  71     ... Some custom initialization here ...
  72
  73     ll_daemon_started(pidfile, fd);
  74
  75     ll_daemon_resetio();   ... this one is optional
  76 }
  77
  78 To stop this daemon:
  79
  80 ll_daemon_stop (lockfilename, pidfile)
  81
  82
  83 ll_daemon_start attempts to start a daemon process going.  It does only
  84 a partial setup.  If it detects that the daemon process is already
  85 running, it itself does an exit(0), not returning to the parent.
  86
  87 If there was a failure starting a daemon process, -1 is return, else
  88 we return a transparent file descriptor, which will have to be passed as
  89 the secodn argument to ll_daemon_started().
  90
  91 When ll_daemon_start returns, we're already running in a partially set-up
  92 daemon process.  The setup isn't complete just yet.  The parent function
  93 can perform any other custom initialization.  If initialization fails,
  94 the parent function can simply exit.  Otherwise, if the initialization
  95 completes, ll_daemon_started must be called in order to save this daemon
  96 process's pid in the pid file (2nd arg must be the return from ll_daemon_start.
  97
  98 To stop a daemon process, simply call ll_daemon_stop.  Nothing too
  99 sophisticated here.
 100
 101 To send the daemon process a SIGHUP, call ll_daemon_restart.
 102 */
 103
 104 #ifdef  __cplusplus
 105 }
 106 #endif
 107
 108 #endif