APM: Perl and C Semaphores

[Brian Michalk]

I posted this to comp.lang.perl  Maybe someone here has a suggestion?

From: michalk at awpi.com (Brian K. Michalk)
Newsgroups: comp.lang.perl
Subject: Semaphore from Perl, used in C (semget problems)
NNTP-Posting-Host: 66.134.114.52
Message-ID: <c30723e3.0211271209.e723ea5 at posting.google.com>

I have a subroutine in a perl module:

    543 ################################################################
    544 sub new_semaphore() {
    545   my $self = shift; if($self->sd(@_)) {return undef;}
    546
    547   if (@_) {
    548     my $s = new IPC::Semaphore(IPC_PRIVATE, 1, S_IRWXU | S_IRWXG |
S_IROTH | IPC_CREAT);
    549     $self->{semaphore} = $s;
    550   }
    551   if (defined $self->{semaphore}) {
    552     return $self->{semaphore}->id();
    553   }
    554 }
    555 ################################################################

That is called from the perl code:
 45 my $sid = $gpr->new_semaphore(1);
 46 $gpr->set_executable($ARGV[0]." -m $id -s $sid -q");

Where ARGV[0] is the name of the C program to run, and the semaphore
id is passed via "-s" on the command line.  My C program looks like
this:

... declarations ...
     61 key_t sem_key = 0;            // semaphore key
... down in the main program ...
    188 main(int argc, char *argv[])
    189 {
...snip...
    194   union semun {
    195     int val;        /* value for SETVAL */
    196     struct semid_ds *buf;    /* buffer for IPC_STAT, IPC_SET */
    197     unsigned short int *array;  /* array for GETALL, SETALL */
    198     struct seminfo *__buf;     /* buffer for IPC_INFO */
    199   } arg;
...process arguments...

    215   while ((argc > 1) && (argv[1][0] == '-')) {
    216     switch (argv[1][1]) {
...snip...
    235       case 's':
    236         argv++;
    237         --argc;
    238         printf("processing S\n");
    239         instring = argv[1];   // memory ID
    240         sem_key = atoi(instring);
    241         printf("sem_key: %d \n", sem_key);
    242         break;
    243     }
    244     argv++;
    245     --argc;
    246   }
... finally to the semget...
    253 #define PERM S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH |
S_IWOTH
    254  sem_id = semget(sem_key, , PERM );
    256  if (sem_id = -1) perror("semget failed--");

When I run the whole mess, I get the following:
semget failed--: No such file or directory
which is the message for ENOENT which according to the semget(2) manpage:
"No semaphore set exists for key and semflg wasn't asserting IPC_CREAT."

I am at a loss.  I've tried many permutations, and trying to attach to
a semaphore listed by ipcs doesn't work either.  I've even gotten a
semget() = -1 result with errno set to success, whatever that means.