Signal handling, take 2.

tests/standalone/io/signals_test_script.dart

+// Copyright (c) 2013, 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:io";
+
+void main(args) {
+  int usr1Count = int.parse(args[0]);
+  int usr2Count = int.parse(args[1]);
+  var sub1;
+  var sub2;
+  void check() {
+    if (usr1Count < 0 || usr2Count < 0) exit(1);
+    if (usr1Count == 0 && usr2Count == 0) {
+      sub1.cancel();
+      sub2.cancel();
+    }
+    print("ready");
+  }
+  sub1 = ProcessSignal.SIGUSR1.watch().listen((signal) {
+    if (signal != ProcessSignal.SIGUSR1) exit(1);
+    usr1Count--;
+    check();
+  });
+  sub2 = ProcessSignal.SIGUSR2.watch().listen((signal) {
+    if (signal != ProcessSignal.SIGUSR2) exit(1);
+    usr2Count--;
+    check();
+  });
+  check();
+}