streams/wvlockdev.cc

   1 /*
   2  * Worldvisions Weaver Software:
   3  *   Copyright (C) 1997-2002 Net Integration Technologies, Inc.
   4  *
   5  * Some handy functions to create/remove /var/lock lockfiles.
   6  */
   7 #include "wvlockdev.h"
   8 #include "wvfile.h"
   9 #include "strutils.h"
  10 #include <signal.h>
  11 #include <string.h>
  12 #include <sys/types.h>
  13 #include <fcntl.h>
  14 #include <sys/stat.h>
  15 #include <errno.h>
  16
  17 WvLockDev::WvLockDev(WvString _devicename)
  18         : devicename(_devicename)
  19 {
  20     const char *p = strrchr(devicename, '/');
  21     if (p)
  22         p++;
  23     else
  24         p = devicename;
  25
  26     lock_count = 0;
  27     filename = WvString("/var/lock/LCK..%s", p);
  28 }
  29
  30
  31 WvLockDev::~WvLockDev()
  32 {
  33     if (lock_count)
  34     {
  35         lock_count = 1;
  36         unlock();
  37     }
  38 }
  39
  40
  41 #if USE_LOCKDEV /* use the liblockdev.a locking routines */
  42
  43 #include <lockdev.h>
  44
  45 bool WvLockDev::lock()
  46 {
  47     if (lock_count)
  48     {
  49         lock_count++;
  50         return true;
  51     }
  52
  53     if (dev_lock(devicename))
  54         return false;
  55
  56     lock_count++;
  57     return true;
  58 }
  59
  60
  61 void WvLockDev::unlock()
  62 {
  63     if (!lock_count) return;
  64
  65     if (!--lock_count)
  66         dev_unlock(devicename, getpid());
  67 }
  68
  69
  70 #else /* !USE_LOCKDEV -- implement our own locking routines */
  71
  72
  73 // note: this function uses the O_EXCL flag to open(), and thus assumes
  74 // that /var/lock is not an NFS-mounted drive (according to the open() man
  75 // page, you need to follow a special procedure to ensure successful NFS
  76 // locking)
  77 //
  78 // Actually there may be other race conditions that we should look into.
  79 bool WvLockDev::lock()
  80 {
  81     pid_t pid;
  82
  83     if (lock_count)
  84     {
  85         lock_count++;
  86         return true;
  87     }
  88
  89     WvFile fd(filename, O_RDWR | O_EXCL | O_CREAT, 0644);
  90
  91     if (fd.isok())
  92     {
  93         // We made a lock file...
  94         fd.print("%10s\n", getpid());
  95     }
  96     else if (fd.geterr() == EEXIST)
  97     {
  98         char *inbuf;
  99
 100         // Lock file is already there!  Check for staleness...
 101         sleep(1);       // preventing race condition...
 102
 103         fd.open(filename, O_RDONLY);
 104         //fprintf(stderr, "ok: %d\n", fd.isok());
 105         inbuf = trim_string(fd.blocking_getline(-1));
 106         //fprintf(stderr, "blocking_getline: '%s'\n", inbuf);
 107
 108         if (inbuf)
 109             pid = atoi(inbuf);
 110         else
 111             pid = 0;
 112
 113         //fprintf(stderr, "pid: '%d'\n", pid);
 114
 115         if (pid && pid != -1 && kill(pid, 0) == -1 && errno == ESRCH)
 116         {
 117             // we can create a lockfile now
 118             fd.close();
 119             if (unlink(filename))
 120                 return false; // cannot remove lockfile
 121             fd.open(filename, O_RDWR | O_EXCL | O_CREAT, 0644);
 122             fd.print("%10s\n", getpid());
 123         }
 124         else
 125             return false; // device already locked
 126     }
 127     else // some other unexpected error
 128         return false;
 129
 130     lock_count++;
 131     return true;
 132 }
 133
 134
 135
 136 void WvLockDev::unlock()
 137 {
 138     if (!lock_count) return;
 139
 140     if (!--lock_count)
 141         unlink(filename);
 142 }
 143
 144
 145 #endif /* !USE_LOCKDEV */