Greetings, follow Monks.

I've been tinkering with some code which flock()s a semaphore file.

With some help from bart in the CB, it appears that shared locks are not available. To quote perldoc -f flock:

Note that the emulation built with lockf(3) doesn't provide shared locks, and it requires that FILEHANDLE be open with write intent. These are the semantics that lockf(3) implements. Most if not all systems implement lockf(3) in terms of fcntl(2) locking, though, so the differing semantics shouldn’t bite too many people.

Unfortunately, I seem to have been bitten. I need both exclusive (LOCK_EX) and shared locks (LOCK_SH).
Changing the permissions on the open statement also causes exclusive locks to fail, as foretold by the perldoc.

I tried recompiling my Perl binary with sh Configure -Ud_flock, but the problem persists.

The test code is shown below. It works as expected on Linux, but not Solaris. I have tried both 5.6.1 and 5.8.0.

On Solaris, the code fails with a Bad file number error.

#!/usr/bin/perl

use strict;
use warnings;

use Fcntl qw(:flock);

my $file = shift;

open (F, "> $file") or die "Unable to open $file: $!";

my $lock_p = flock(F, LOCK_SH | LOCK_NB);

if ($lock_p) {
    print "Got shared lock on semaphore file!";
    my $wait = <>; # For testing - hold lock.
    flock(F, LOCK_UN) or warn "Problems unlocking $file: $!";
    exit 0;
} else {
    die "Ack! Didn't get a shared lock on $file: $!";
}
[download]

My questions are as follows:

• Is there a way to make both shared and exclusive locks work using Perl's flock on Solaris?
• Have I done all that needs to be done with the recompile, or did I miss something?
• Will I have to resort to Inline::C?
• If I have to use Inline::C, can I mix plain perl flock() for exclusive locks with Inline::C code for shared locks, or am I better just handling all locking from the C side? (The latter is tidier, if nothing else).

Cheers in advance,

BazB

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