lib/other/lock.c

   1 #include <lib.h>
   2 #include <errno.h>
   3 #include <sys/types.h>
   4 #include <unistd.h>
   5 #include <string.h>
   6 #include <fcntl.h>
   7 #include <stdio.h>
   8 #if _ANSI
   9 #include <stdlib.h>
  10 #endif
  11
  12 typedef enum {
  13   False, True
  14 } BOOLEAN;
  15
  16 #define LOCKDIR "/tmp/"         /* or /usr/tmp/ as the case may be */
  17 #define MAXTRIES 3
  18 #define NAPTIME (unsigned int)5
  19
  20 PRIVATE _PROTOTYPE( char *lockpath, (char *name));
  21 _PROTOTYPE( void syserr, (char *errstring));
  22 _PROTOTYPE( BOOLEAN lock, (char *name));
  23 _PROTOTYPE( void unlock, (char *name));
  24
  25 void
  26 syserr(errstring)
  27 char *errstring;
  28 {
  29         fprintf(stderr,"couldn't %s\n", errstring);
  30         exit(1);
  31 }
  32
  33 BOOLEAN lock(name)              /* acquire lock */
  34 char *name;
  35 {
  36   char *path;
  37   int fd, tries;
  38
  39   path = lockpath(name);
  40   tries = 0;
  41   while ((fd = creat(path, 0)) == -1 && errno == EACCES) {
  42         if (++tries >= MAXTRIES) return(False);
  43         sleep(NAPTIME);
  44   }
  45   if (fd == -1 || close(fd) == -1) syserr("lock");
  46   return(True);
  47 }
  48
  49 void unlock(name)               /* free lock */
  50 char *name;
  51 {
  52   if (unlink(lockpath(name)) == -1) syserr("unlock");
  53 }
  54
  55 PRIVATE char *lockpath(name)    /* generate lock file path */
  56 char *name;
  57 {
  58   PRIVATE char path[20];
  59
  60   strcpy(path, LOCKDIR);
  61   return(strcat(path, name));
  62 }