void setCallback( SV *cb1, SV* cb2, SV *cb3, SV *cb4 ) {
    int i;
    saved = Perl_get_context();
    callbacks[0] = cb1; SvREFCNT_inc( cb1 );
    callbacks[1] = cb2; SvREFCNT_inc( cb2 );
    callbacks[2] = cb3; SvREFCNT_inc( cb2 );
    callbacks[3] = cb4; SvREFCNT_inc( cb2 );
    for( i=1; i < 4; ++i ) InitializeSRWLock( &locks[ i ] );
    _beginthread( &thread1, 0, NULL );
    _beginthread( &thread2, 0, NULL );
    return;
}

END_C
$|++;

{
    package fred;
    my @c = (0) x 4;

    sub callback1 { ++$c[0]; print "PCB1: $_[0] ($c[0])"; return; }
    sub callback2 { ++$c[1]; print "PCB2: $_[0] ($c[1])"; return; }
    sub callback3 { ++$c[2]; print "PCB3: $_[0] ($c[2])"; return; }
    sub callback4 { ++$c[3]; print "PCB4: $_[0] ($c[3])"; return; }
}

setCallback( \&fred::callback1, \&fred::callback2, \&fred::callback3, \&fred::callback4 );

sleep 100;