Perl: Use of “flock”

daniel — Wed, 10 Dec 2008 21:31:39 +0000

This is a small example on flock. It may help you to prevent multiple running instances of the same script. Assume you run the script via cron and it may not be finished when cron attempts to start it again. This few lines of code solve this issue.

if ( ! open( LOCK, ">/var/run/my_app.lock" ) ) {
    print "Failed to open lock file: $!\n";
    exit(1);
}
 
## Create exclusive, non blocking lock: LOCK_EX(2) + LOCK_NB(4)
if ( ! flock( LOCK, 6 ) ) {
    close( LOCK );
 
    if ( ! open( PID, " ) ) {
 
        print "Failed to read PID file: $!\n";
        exit(1);
    }
 
    my $pid = ;
    close( PID );
 
    print "Failed to accquire lock. Another instance (PID $pid) running!\n";
    exit(1);
}
else {
    if ( ! open( PID, ">/var/run/my_app.pid" ) ) {
 
        print "Failed to open pid file: $!\n";
        exit(1);
    }
 
    print PID $$;
 
    if ( ! close( PID ) ) {
        print "Failed to write PID file: $!\n";
        exit(1);
    }
}

That’s it!

Portage: Patch existing Perl module ebuild by using a overlay

daniel — Wed, 10 Dec 2008 19:19:09 +0000

You may have had the same issue as i some time ago. You install a perl module from Portage but you have to modify the module’s code. Of course you don’t want to patch and install manually. Assuming the module is named “foobar” here’s how i solved it:

Create a Portage Overlay (refer to the official documentation) and enable it in /etc/make.conf
Create a new category directory within your overlay dir (mkdir /usr/local/portage/my-ebuilds)
Create application directory (mkdir /usr/local/portage/my-ebuilds/foobar)
Copy the existing ebuild to the new app directory
Create a files directory and put the patch there
Modify the ebuild to apply your patch

...
 
# This is the magic line:
PATCHES="${FILESDIR}/my_patch.patch"
 
...

After you finished these tasks you have to (re)generate the Manifest:

ebuild [OVERLAY_PATH]/my-ebuilds/foobar/foobar-1.0.0.ebuild digest

That’s it. If you have trouble feel free to contact me: daniel@linuxaddicted.de

My two ¢'s » Perl

Perl: Use of “flock”

Portage: Patch existing Perl module ebuild by using a overlay