
set f [open "|sleep 5" r+];
fconfigure $f -blocking 0;

proc handler {file mode} {
  puts "called handler for $file : $mode";
  if {"r"==$mode} {
    exit;
  } else {
    puts $file "123456789";
  }
}

fileevent $f writable "handler $f w";
fileevent $f readable "handler $f r";

vwait forever;
