Revert "Don't zone-register async callbacks for every await call in the VM."

runtime/lib/core_patch.dart

Index: runtime/lib/core_patch.dart
diff --git a/runtime/lib/core_patch.dart b/runtime/lib/core_patch.dart
index 79749fdbffb09c2f0c69d05c28814f6f06c1bed2..2a45ae708efed16d1b8b4276978c5a8cd8b28de5 100644
--- a/runtime/lib/core_patch.dart
+++ b/runtime/lib/core_patch.dart
@@ -8,6 +8,12 @@ import "dart:typed_data";
 // Equivalent of calling FATAL from C++ code.
 _fatal(msg) native "DartCore_fatal";
 
+// We need to pass the exception and stack trace objects as second and third
+// parameter to the continuation.  See vm/ast_transformer.cc for usage.
+void  _asyncCatchHelper(catchFunction, continuation) {
+  catchFunction((e, s) => continuation(null, e, s));
+}
+
 // The members of this class are cloned and added to each class that
 // represents an enum type.
 class _EnumHelper {
@@ -20,6 +26,132 @@ class _EnumHelper {
   int get hashCode => _enum_names[index].hashCode;
 }
 
+
+// _AsyncStarStreamController is used by the compiler to implement
+// async* generator functions.
+class _AsyncStarStreamController {
+  StreamController controller;
+  Function asyncStarBody;
+  bool isAdding = false;
+  bool onListenReceived = false;
+  bool isScheduled = false;
+  bool isSuspendedAtYield = false;
+  Completer cancellationCompleter = null;
+
+  Stream get stream => controller.stream;
+
+  void runBody() {
+    isScheduled = false;
+    isSuspendedAtYield = false;
+    asyncStarBody();
+  }
+
+  void scheduleGenerator() {
+    if (isScheduled || controller.isPaused || isAdding) {
+      return;
+    }
+    isScheduled = true;
+    scheduleMicrotask(runBody);
+  }
+
+  // Adds element to steam, returns true if the caller should terminate
+  // execution of the generator.
+  //
+  // TODO(hausner): Per spec, the generator should be suspended before
+  // exiting when the stream is closed. We could add a getter like this:
+  // get isCancelled => controller.hasListener;
+  // The generator would translate a 'yield e' statement to
+  // controller.add(e);
+  // suspend;
+  // if (controller.isCancelled) return;
+  bool add(event) {
+    if (!onListenReceived) _fatal("yield before stream is listened to!");
+    if (isSuspendedAtYield) _fatal("unexpected yield");
+    // If stream is cancelled, tell caller to exit the async generator.
+    if (!controller.hasListener) {
+      return true;
+    }
+    controller.add(event);
+    scheduleGenerator();
+    isSuspendedAtYield = true;
+    return false;
+  }
+
+  // Adds the elements of stream into this controller's stream.
+  // The generator will be scheduled again when all of the
+  // elements of the added stream have been consumed.
+  // Returns true if the caller should terminate
+  // execution of the generator.
+  bool addStream(Stream stream) {
+    if (!onListenReceived) _fatal("yield before stream is listened to!");
+    // If stream is cancelled, tell caller to exit the async generator.
+    if (!controller.hasListener) return true;
+    isAdding = true;
+    var whenDoneAdding =
+        controller.addStream(stream as Stream, cancelOnError: false);
+    whenDoneAdding.then((_) {
+      isAdding = false;
+      scheduleGenerator();
+    });
+    return false;
+  }
+
+  void addError(error, stackTrace) {
+    if ((cancellationCompleter != null) && !cancellationCompleter.isCompleted) {
+      // If the stream has been cancelled, complete the cancellation future
+      // with the error.
+      cancellationCompleter.completeError(error, stackTrace);
+      return;
+    }
+    // If stream is cancelled, tell caller to exit the async generator.
+    if (!controller.hasListener) return;
+    controller.addError(error, stackTrace);
+    // No need to schedule the generator body here. This code is only
+    // called from the catch clause of the implicit try-catch-finally
+    // around the generator body. That is, we are on the error path out
+    // of the generator and do not need to run the generator again.
+  }
+
+  close() {
+    if ((cancellationCompleter != null) && !cancellationCompleter.isCompleted) {
+      // If the stream has been cancelled, complete the cancellation future
+      // with the error.
+      cancellationCompleter.complete();
+    }
+    controller.close();
+  }
+
+  _AsyncStarStreamController(this.asyncStarBody) {
+    controller = new StreamController(onListen: this.onListen,
+                                      onResume: this.onResume,
+                                      onCancel: this.onCancel);
+  }
+
+  onListen() {
+    assert(!onListenReceived);
+    onListenReceived = true;
+    scheduleGenerator();
+  }
+
+  onResume() {
+    if (isSuspendedAtYield) {
+      scheduleGenerator();
+    }
+  }
+
+  onCancel() {
+    if (controller.isClosed) {
+      return null;
+    }
+    if (cancellationCompleter == null) {
+      cancellationCompleter = new Completer();
+      scheduleGenerator();
+    }
+    return cancellationCompleter.future;
+  }
+}
+
+
 // _SyncIterable and _syncIterator are used by the compiler to
 // implement sync* generator functions. A sync* generator allocates
 // and returns a new _SyncIterable object.