static long dm_evalOnOtherMachineWithReturnValue_timeout = 60000;

sO dm_evalOnOtherMachineWithReturnValue(fS computerID, S code, O... _) {
  fS id = aGlobalID();
  final new Var<Either<O, S>> var;
  temp vmBus_onMessage('gotFromPrivateChat, voidfunc(S sender, S msg) {
    if (var.has() || neq(sender, computerID)) ret;
    new Matches m;
    if (!startsWith(msg, "done " + id + " ", m)) ret;
    if (neq(getAuthorOfSignedText(msg), computerID)) {
      File f = javaxCachesDir("failed-eval-msg-" + computerID);
      saveTextFile(f, msg);
      var.set((Either) eitherB("eval result from " + computerID + " did not verify, saved as " + f));
    }
    S s = firstLine(m.rest());
    if (startsWith(s, "direct: ", m))
      var.set((Either) eitherA(m.rest()));
    else if (startsWith(s, "quoted: ", m))
      var.set((Either) eitherA(unquote(m.rest())));
    else if (startsWith(s, "base64: ", m))
      var.set((Either) eitherA(base64decode(m.rest())));
    else if (startsWith(s, "error: ", m))
      var.set((Either) eitherB(m.rest()));
    else
      var.set((Either) eitherB("unknown mode"));
  });
  dm_privateChat_sendSigned(computerID, computerID + " eval "
    + (boolOptPar(_, 'realEval) ? "real " : "")
    + (boolOptPar(_, 'fresh) ? "fresh " : "")
    + id + ": " + code);
  Either<O, S> e = waitForVarToBeNotNullWithTimeout(var, dm_evalOnOtherMachineWithReturnValue_timeout);
  
  if (boolPar updateControllableFlag(_))
    dm_pcall('controllableComputerList, 'setControllableByMe, computerID, eitherIsA(e));
 
  if (e == null) fail("timeout");
  if (eitherIsB(e)) fail(eitherGetB(e));
  ret eitherGetA(e);
}

Began life as a copy of #1019606