Perl / flock oddity

[Mark Poeschl_2]

I don't know if this is a "feature" of perl, or just an oddity of perl on Tru64 but I thought I'd post here and see if it rings any bells with anyone.

Tru64 5.1B / Patch Kit 4

I'm trying to use the 'flock' system call from within a perl script. The code is attached. It turns out that if I don't explicity reset the OS_ERROR variable '$!' in the program, it never detects that the lock has been released. I.E. with the line commented out as in the attachment, the second and all subsequent invocations of the program just wait in the 15 second loop indefinitely. If you uncomment the line '$! = 0;' it works just fine.

Does this make sense to anybody? What am I missing?

TIA...

[Sreedhar_12]

Hello,

I tried executing the attached program. It works as expected (even with commenting the statement " $! == 0; ". I tested on system with V5.1B + patchkit4. Can you let us knwo the version of the perl you are using "perl -v". Logs are attached.

/Sreedhar

[Mark Poeschl_2]

Thanks Sreedhar - I'm on perl 5.8.0 as well. Your logs show only one invocation of the program. Are you seeing expected behavior with multiple invocations as well? I only have a problem with multiple simultaneous runs of the program.

[Michael Schulte zur Sur]

Mark,

as my perl book says, $! is only set in case of an os system error. You probably have to reset it yourself.

greetings,

Michael

[Sreedhar_12]

Hi Mark,

I am able to reproduce the reported problem with multiple invocations. I tested in other flavours of UNIX (Solaris and HP-UX). Logs are attached. There perl is behaving differently. No difference is seen in behaviour with/with out commenting out the statement "$! == 0".

/Sreedhar

[Michael Schulte zur Sur · Accepted solution]

Hi,

the code should work as follows.
Got that with the help of procura.

greetings,

Michael


if (flock (HANDLE, (LOCK_EX|LOCK_NB)))
{
print STDOUT "Lock acquired - sleeping for one minute\n" ;
$waiting = 0;
sleep 60 ;
} else
{
if ( $! == EWOULDBLOCK )
{
...

[Mark Poeschl_2]

Perfect - thanks Michael.