svsem/svsem_op.c

This is svsem/svsem_op.c (Listing 47-8, page 982), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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  Cover of The Linux Programming Interface
+/* svsem_op.c
+
+   Perform groups of operations on a System V semaphore set.
+
+   Usage as shown in usageError().
+*/
 #include <sys/types.h>
 #include <sys/sem.h>
 #include <ctype.h>
 #include "curr_time.h"          /* Declaration of currTime() */
 #include "tlpi_hdr.h"
 
 #define MAX_SEMOPS 1000         /* Maximum operations that we permit for
                                    a single semop() */
 
 static void
 usageError(const char *progName)
 {
     fprintf(stderr, "Usage: %s semid op[,op...] ...\n\n", progName);
     fprintf(stderr, "'op' is either: <sem#>{+|-}<value>[n][u]\n");
     fprintf(stderr, "            or: <sem#>=0[n]\n");
     fprintf(stderr, "       \"n\" means include IPC_NOWAIT in 'op'\n");
     fprintf(stderr, "       \"u\" means include SEM_UNDO in 'op'\n\n");
     fprintf(stderr, "The operations in each argument are "
                     "performed in a single semop() call\n\n");
     fprintf(stderr, "e.g.: %s 12345 0+1,1-2un\n", progName);
     fprintf(stderr, "      %s 12345 0=0n 1+1,2-1u 1=0\n", progName);
     exit(EXIT_FAILURE);
 }
 
 /* Parse comma-delimited operations in 'arg', returning them in the
    array 'sops'. Return number of operations as function result. */
 
 static int
 parseOps(char *arg, struct sembuf sops[])
 {
     char *comma, *sign, *remaining, *flags;
     int numOps;                 /* Number of operations in 'arg' */
 
     for (numOps = 0, remaining = arg; ; numOps++) {
         if (numOps >= MAX_SEMOPS)
             cmdLineErr("Too many operations (maximum=%d): \"%s\"\n",
                         MAX_SEMOPS, arg);
 
         if (*remaining == '\0')
             fatal("Trailing comma or empty argument: \"%s\"", arg);
         if (!isdigit((unsigned char) *remaining))
             cmdLineErr("Expected initial digit: \"%s\"\n", arg);
 
         sops[numOps].sem_num = strtol(remaining, &sign, 10);
 
         if (*sign == '\0' || strchr("+-=", *sign) == NULL)
             cmdLineErr("Expected '+', '-', or '=' in \"%s\"\n", arg);
         if (!isdigit((unsigned char) *(sign + 1)))
             cmdLineErr("Expected digit after '%c' in \"%s\"\n", *sign, arg);
 
         sops[numOps].sem_op = strtol(sign + 1, &flags, 10);
 
         if (*sign == '-')                       /* Reverse sign of operation */
             sops[numOps].sem_op = - sops[numOps].sem_op;
         else if (*sign == '=')                  /* Should be '=0' */
             if (sops[numOps].sem_op != 0)
                 cmdLineErr("Expected \"=0\" in \"%s\"\n", arg);
 
         sops[numOps].sem_flg = 0;
         for (;; flags++) {
             if (*flags == 'n')
                 sops[numOps].sem_flg |= IPC_NOWAIT;
             else if (*flags == 'u')
                 sops[numOps].sem_flg |= SEM_UNDO;
             else
                 break;
         }
 
         if (*flags != ',' && *flags != '\0')
             cmdLineErr("Bad trailing character (%c) in \"%s\"\n", *flags, arg);
 
         comma = strchr(remaining, ',');
         if (comma == NULL)
             break;                              /* No comma --> no more ops */
         else
             remaining = comma + 1;
     }
 
     return numOps + 1;
 }
 
 int
 main(int argc, char *argv[])
 {
     struct sembuf sops[MAX_SEMOPS];
     int ind, nsops;
 
     if (argc < 2 || strcmp(argv[1], "--help") == 0)
         usageError(argv[0]);
 
     for (ind = 2; argv[ind] != NULL; ind++) {
         nsops = parseOps(argv[ind], sops);
 
         printf("%5ld, %s: about to semop()  [%s]\n", (long) getpid(),
                 currTime("%T"), argv[ind]);
 
         if (semop(getInt(argv[1], 0, "semid"), sops, nsops) == -1)
             errExit("semop (PID=%ld)", (long) getpid());
 
         printf("%5ld, %s: semop() completed [%s]\n", (long) getpid(),
                 currTime("%T"), argv[ind]);
     }
 
     exit(EXIT_SUCCESS);
 }

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