Question

I am developing a record storage system which stores scanned, indexed and encrypted records in physical boxes.

I have a method say “getAvailablePlace()” which checks what box and what seq is available for store. I want to lock this method. Ie when one user is entered into this method and he gets box:12 seq:55 as empty place..simultaneously at same time another user is accessing same method he may also get same values..box:12 seq:55 which is error prone.

So if I can lock this method when one user is already into this process?

I am using SQLite, wamp and codeigniter.

Answer 1

I have this code in use:

define('LOCK_FILE', "/path/to/your/lockfile-".$argv[1].".lock");
if( isLocked() ) die("ALREADY RUNNING !!!!\n" );

function isLocked()
{
    # If lock file exists, check if stale.  If exists and is not stale, return TRUE
    # Else, create lock file and return FALSE.

    if( file_exists( LOCK_FILE ) )
    {
        # check if it's stale
        $lockingPID = trim( file_get_contents( LOCK_FILE ) );

       # Get all active PIDs.
        $pids = explode( "\n", trim( `ps -e | awk '{print $1}'` ) );

        # If PID is still active, return true
        if( in_array( $lockingPID, $pids ) )  return true;

        # Lock-file is stale, so kill it.  Then move on to re-creating it.
        echo "Removing stale lock file.\n";
        unlink( LOCK_FILE );
    }

    file_put_contents( LOCK_FILE, getmypid() . "\n" );
    return false;
} 

You may alter it not to check the pid and just use the file as lock info.