fcn reader(fileName,out){
   n:=0; foreach line in (File(fileName)) { out.write(line); n+=1; }
   out.close();	// signal done
   Atomic.waitFor(out.Property("isOpen")); // wait for other thread to reopen Pipe
   out.write(n);
}
fcn writer(in){
   Utils.zipWith(fcn(n,line){ "%3d: %s".fmt(n,line).print() },[1..],in);
   in.open();  // signal other thread to send num lines read
   println("Other thread read ",in.read()," lines");
}

p:=Thread.Pipe();  // NOT Unix pipes, thread safe channel between threads
reader.launch("input.txt",p);
writer.future(p).noop();  // noop forces eval, ie sleep until writer finished