Add Isolate ping functionality.

tests/isolate/ping_test.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:isolate";
+import "dart:async";
+import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+
+isomain1(replyPort) {
+  RawReceivePort port = new RawReceivePort();
+  port.handler = (v) {
+    replyPort.send(v);
+    if (v == 0) port.close();
+  };
+  replyPort.send(port.sendPort);
+}
+
+void main(){
+  asyncStart();
+  var completer = new Completer();  // Completed by first reply from isolate.
+  RawReceivePort reply = new RawReceivePort(completer.complete);
+  Isolate.spawn(isomain1, reply.sendPort).then((Isolate isolate) {
+    List result = [];
+    completer.future.then((echoPort) {
+      reply.handler = (v) {
+        result.add(v);
+        if (v == 0) {
+          Expect.listEquals(["alive", "control", 4, 3, 2, "event", 1, 0],
+                            result);
+          reply.close();
+          asyncEnd();
+        }
+      };
+      echoPort.send(4);
+      isolate.ping((new ReceivePort()
+                        ..first.then((_) { result.add("alive"); })).sendPort,

[floitsch, 2014/03/04 12:12:51]

You can't guarantee that "alive" will be before 4.
If the other isolate is fast enough it will have already handled the
echoPort.send(4).

Same for the the control one.

[Lasse Reichstein Nielsen, 2014/03/06 12:47:17]

Ack, true.
Rewritten to check that  
  4 <- 3 <- 2 <- 1 <- 0   (read "<-" as "comes before")
  "alive" <- 3
  "control" <- 2
  2 <- "event" <- 1

+                   Isolate.PING_ALIVE);
+      echoPort.send(3);
+      isolate.ping((new ReceivePort()
+                        ..first.then((_) { result.add("control"); })).sendPort,
+                   Isolate.PING_CONTROL);
+      echoPort.send(2);
+      isolate.ping((new ReceivePort()
+                        ..first.then((_) { result.add("event"); })).sendPort,
+                   Isolate.PING_EVENT);
+      echoPort.send(1);
+      echoPort.send(0);
+    });
+  });
+}