#!/usr/bin/perl
#
# This is the file locking routines which come with Agora.  Code is
# either partially modified or directly ripped from that program.
#
# Agora is by Arthur Secret <secret@w3.org> and Hugh Sasse
# <hgs@dmu.ac.uk>.  Agora's copyright is at
# http://www.w3.org/hypertext/COPYRIGHT.html.
#


# SetLockFile(Directory, Filename)
#
# Returns 1 on success, 0 on error.
sub SetLockFile
{
    local($Dir, $FileName) = @_;
    local($have_exclusive_lock) = 0;

    srand $$;

    while(!$have_exclusive_lock)
    {
        # Is there a lockfile?
        opendir(LOCKDIR, "$Dir") || return 0;
        @lockfiles = readdir(LOCKDIR);
        closedir(LOCKDIR);

        @lockfiles = grep(($_ =~ /${FileName}_[0-9]+.lck/i), @lockfiles);

        if( $#lockfiles == -1)
        {
            # there are none here already, so we can create one.
            open(LOCKFILE, ">$Dir/${FileName}_$$.lck") ||
	        return 0;
            print LOCKFILE "Lock file\n";
            close(LOCKFILE);

            ## So we have now created a lock file.  We
            # may still not have an exclusive lock. Another
	    # process may have got the lock at the same time.

            opendir(LOCKDIR, "$Dir") || return 0;
	    @lockfiles = readdir(LOCKDIR);  
	    closedir(LOCKDIR); 
 
	    @lockfiles = grep(($_ =~ /${FileName}_[0-9]+.lck/i),
		@lockfiles);

            if($#lockfiles == 0)
            {
               # there is only one lock file so it must be
	       # ours.
               $have_exclusive_lock = 1;
            } 
            else
            {
               # we need to remove the lockfile we have made...
               unlink("$Dir/${FileName}_$$.lck") || return 0;
               # and wait a random length of time.
               sleep(rand($$ % 3));
            }; # end if $#lockfiles == 0 ...else..
        }
        else
        {
            # there is a lock file.
            # wait a random length of time.
            sleep(rand($$ % 3));
        }; # end if ($#lockfiles == -1) ... else....

    }; # end while(!$have_exclusive_lock)

    # there is only one lockfile -- ours -- so we can proceed
    return "$Dir/${FileName}_$$.lck";
}; # end sub quota_write_file();

1;  # Must be the last line