tLOCK.c - plan9port - [fork] Plan 9 from user space
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       ---
       tLOCK.c (1065B)
       ---
            1 #include <u.h>
            2 #include <libc.h>
            3 
            4 /* MAXHOSTNAMELEN is in sys/param.h */
            5 #define MAXHOSTNAMELEN        64
            6 
            7 char lockstring[MAXHOSTNAMELEN+8];
            8 
            9 void
           10 main(int argc, char *argv[]) {
           11         char *lockfile;
           12         int fd, ppid, ssize;
           13         struct Dir *statbuf;
           14 
           15         if (argc != 4) {
           16                 fprint(2, "usage: LOCK lockfile hostname ppid\n");
           17                 exits("lock failed on usage");
           18         }
           19         lockfile = argv[1];
           20         if ((fd=create(lockfile, OLOCK|ORDWR, 0666)) < 0) {
           21                 exits("lock failed on create");
           22         }
           23         ppid = atoi(argv[3]);
           24         ssize = sprint(lockstring, "%s %s\n", argv[2], argv[3]);
           25         if (write(fd, lockstring, ssize) != ssize) {
           26                 fprint(2, "LOCK:write(): %r\n");
           27                 exits("lock failed on write to lockfile");
           28         }
           29 
           30         switch(fork()) {
           31         default:
           32                 exits("");
           33         case 0:
           34                 break;
           35         case -1:
           36                 fprint(2, "LOCK:fork(): %r\n");
           37                 exits("lock failed on fork");
           38         }
           39 
           40         for(;;) {
           41                 statbuf = dirfstat(fd);
           42                 if(statbuf == nil)
           43                         break;
           44                 if (statbuf->length == 0){
           45                         free(statbuf);
           46                         break;
           47                 }
           48                 free(statbuf);
           49                 if (write(fd, "", 0) < 0)
           50                         break;
           51                 sleep(3000);
           52         }
           53 
           54         close(fd);
           55         postnote(PNGROUP, ppid, "kill");
           56         exits("");
           57 }