Big merge from experimental to bleeding edge.

tests/lib/async/slow_consumer_test.dart

+// Copyright (c) 2012, 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.
+
+// VMOptions=--old_gen_heap_size=32
+
+import 'dart:async';
+import 'dart:isolate';
+
+const int KB = 1024;
+const int MB = KB * KB;
+const int GB = KB * KB * KB;
+
+class SlowConsumer extends StreamConsumer {
+  var current = new Future.immediate(0);
+  final int bytesPerSecond;
+
+  SlowConsumer(int this.bytesPerSecond);
+
+  Future consume(Stream stream) {
+    Completer completer = new Completer();
+    var subscription;
+    subscription = stream.listen(
+      (List<int> data) {
+        current = current
+          .then((count) {
+            // Simulated amount of time it takes to handle the data.
+            int ms = data.length * 1000 ~/ bytesPerSecond;
+            subscription.pause();
+            return new Future.delayed(ms, () {
+              subscription.resume();
+              // Make sure we use data here to keep tracking it.
+              return count + data.length;
+            });
+          });
+        },
+      onDone: () { current.then((count) { completer.complete(count); }); });
+    return completer.future;
+  }
+}
+
+class DataProvider extends StreamController {
+  final int chunkSize;
+  final int bytesPerSecond;
+  int sentCount = 0;
+  int targetCount;
+
+  DataProvider(int this.bytesPerSecond, int this.targetCount, this.chunkSize) {
+    new Timer(0, (_) => send());
+  }
+
+  send() {
+    if (isPaused) return;
+    if (sentCount == targetCount) {
+      close();
+      return;
+    }
+    int listSize = chunkSize;
+    sentCount += listSize;
+    if (sentCount > targetCount) {
+      listSize -= sentCount - targetCount;
+      sentCount = targetCount;
+    }
+    add(new List.fixedLength(listSize));
+    int ms = listSize * 1000 ~/ bytesPerSecond;
+    if (!isPaused) new Timer(ms, (_) => send());
+  }
+
+  onPauseStateChange() {
+    // We don't care if we just unpaused or paused. In either case we just
+    // call send which will test it for us.
+    send();
+  }
+}
+
+main() {
+  var port = new ReceivePort();
+  // The data provider can deliver 800MB/s of data. It sends 100MB of data to
+  // the slower consumer who can only read 200MB/s. The data is sent in 1MB
+  // chunks.
+  //
+  // This test is limited to 32MB of heap-space (see VMOptions on top of the
+  // file). If the consumer doesn't pause the data-provider it will run out of
+  // heap-space.
+
+  new DataProvider(800 * MB, 100 * MB, 1 * MB)
+    .pipe(new SlowConsumer(200 * MB))
+    .then((count) {
+      port.close();
+      Expect.equals(100 * MB, count);
+    });
+}