vipunen/patched_sdk/lib/isolate/isolate.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.

/**
 * Concurrent programming using _isolates_:
 * independent workers that are similar to threads
 * but don't share memory,
 * communicating only via messages.
 *
 * To use this library in your code:
 *
 *     import 'dart:isolate';
 */
library dart.isolate;

import "dart:async";
import "dart:collection" show HashMap;
import "dart:_internal" hide Symbol;

part "capability.dart";

/**
 * Thrown when an isolate cannot be created.
 */
class IsolateSpawnException implements Exception {
  /** Error message reported by the spawn operation. */
  final String message;
  IsolateSpawnException(this.message);
  String toString() => "IsolateSpawnException: $message";
}

/**
 * An isolated Dart execution context.
 *
 * All Dart code runs in an isolate, and code can access classes and values
 * only from the same isolate. Different isolates can communicate by sending
 * values through ports (see [ReceivePort], [SendPort]).
 *
 * An `Isolate` object is a reference to an isolate, usually different from
 * the current isolate.
 * It represents, and can be used control, the other isolate.
 *
 * When spawning a new isolate, the spawning isolate receives an `Isolate`
 * object representing the new isolate when the spawn operation succeeds.
 *
 * Isolates run code in its own event loop, and each event may run smaller tasks
 * in a nested microtask queue.
 *
 * An `Isolate` object allows other isolates to control the event loop
 * of the isolate that it represents, and to inspect the isolate,
 * for example by pausing the isolate or by getting events when the isolate
 * has an uncaught error.
 *
 * The [controlPort] identifies and gives access to controlling the isolate,
 * and the [pauseCapability] and [terminateCapability] guard access
 * to some control operations.
 * For example, calling [pause] on an `Isolate` object created without a
 * [pauseCapability], has no effect.
 *
 * The `Isolate` object provided by a spawn operation will have the
 * control port and capabilities needed to control the isolate.
 * New isolate objects can be created without some of these capabilities
 * if necessary, using the [Isolate.Isolate] constructor.
 *
 * An `Isolate` object cannot be sent over a `SendPort`, but the control port
 * and capabilities can be sent, and can be used to create a new functioning
 * `Isolate` object in the receiving port's isolate.
 */
class Isolate {
  /** Argument to `ping` and `kill`: Ask for immediate action. */
  static const int IMMEDIATE = 0;
  /** Argument to `ping` and `kill`: Ask for action before the next event. */
  static const int BEFORE_NEXT_EVENT = 1;

  /**
   * Control port used to send control messages to the isolate.
   *
   * The control port identifies the isolate.
   *
   * An `Isolate` object allows sending control messages
   * through the control port.
   *
   * Some control messages require a specific capability to be passed along
   * with the message (see [pauseCapability] and [terminateCapability]),
   * otherwise the message is ignored by the isolate.
   */
  final SendPort controlPort;

  /**
   * Capability granting the ability to pause the isolate.
   *
   * This capability is required by [pause].
   * If the capability is `null`, or if it is not the correct pause capability
   * of the isolate identified by [controlPort],
   * then calls to [pause] will have no effect.
   *
   * If the isolate is spawned in a paused state, use this capability as
   * argument to the [resume] method in order to resume the paused isolate.
   */
  final Capability pauseCapability;

  /**
   * Capability granting the ability to terminate the isolate.
   *
   * This capability is required by [kill] and [setErrorsFatal].
   * If the capability is `null`, or if it is not the correct termination
   * capability of the isolate identified by [controlPort],
   * then calls to those methods will have no effect.
   */
  final Capability terminateCapability;

  /**
   * Create a new [Isolate] object with a restricted set of capabilities.
   *
   * The port should be a control port for an isolate, as taken from
   * another `Isolate` object.
   *
   * The capabilities should be the subset of the capabilities that are
   * available to the original isolate.
   * Capabilities of an isolate are locked to that isolate, and have no effect
   * anywhere else, so the capabilities should come from the same isolate as
   * the control port.
   *
   * Can also be used to create an [Isolate] object from a control port, and
   * any available capabilities, that have been sent through a [SendPort].
   *
   * Example:
   * ```dart
   * Isolate isolate = findSomeIsolate();
   * Isolate restrictedIsolate = new Isolate(isolate.controlPort);
   * untrustedCode(restrictedIsolate);
   * ```
   * This example creates a new `Isolate` object that cannot be used to
   * pause or terminate the isolate. All the untrusted code can do is to
   * inspect the isolate and see uncaught errors or when it terminates.
   */
  Isolate(this.controlPort, {this.pauseCapability, this.terminateCapability});

  /**
   * Return an [Isolate] object representing the current isolate.
   *
   * The current isolate for code using [current]
   * is the isolate running the code.
   *
   * The isolate object provides the capabilities required to inspect,
   * pause or kill the isolate, and allows granting these capabilities
   * to others.
   *
   * It is possible to pause the current isolate, but doing so *without*
   * first passing the ability to resume it again to another isolate,
   * is a sure way to hang your program.
   */
  static Isolate get current => _currentIsolate;

  /**
   * Returns the package root of the current isolate, if any.
   *
   * If the isolate is using a [packageConfig] or the isolate has not been
   * setup for package resolution, this getter returns `null`, otherwise it
   * returns the package root - a directory that package URIs are resolved
   * against.
   */
  static Future<Uri> get packageRoot {
    var hook = VMLibraryHooks.packageRootUriFuture;
    if (hook == null) {
      throw new UnsupportedError("Isolate.packageRoot");
    }
    return hook();
  }

  /**
   * Returns the package root of the current isolate, if any.
   *
   * If the isolate is using a [packageRoot] or the isolate has not been
   * setup for package resolution, this getter returns `null`, otherwise it
   * returns the package config URI.
   */
  static Future<Uri> get packageConfig {
    var hook = VMLibraryHooks.packageConfigUriFuture;
    if (hook == null) {
      throw new UnsupportedError("Isolate.packageConfig");
    }
    return hook();
  }

  /**
   * Maps a package: URI to a non-package Uri.
   *
   * If there is no valid mapping from the package: URI in the current
   * isolate, then this call returns `null`. Non-package: URIs are
   * returned unmodified.
   */
  static Future<Uri> resolvePackageUri(Uri packageUri) {
    var hook = VMLibraryHooks.resolvePackageUriFuture;
    if (hook == null) {
      throw new UnsupportedError("Isolate.resolvePackageUri");
    }
    return hook(packageUri);
  }

  /**
   * Creates and spawns an isolate that shares the same code as the current
   * isolate.
   *
   * The argument [entryPoint] specifies the initial function to call
   * in the spawned isolate.
   * The entry-point function is invoked in the new isolate with [message]
   * as the only argument.
   *
   * The function must be a top-level function or a static method
   * that can be called with a single argument,
   * that is, a compile-time constant function value
   * which accepts at least one positional parameter
   * and has at most one required positional parameter.
   * The function may accept any number of optional parameters,
   * as long as it *can* be called with just a single argument.
   * The function must not be the value of a function expression
   * or an instance method tear-off.
   *
   * Usually the initial [message] contains a [SendPort] so
   * that the spawner and spawnee can communicate with each other.
   *
   * If the [paused] parameter is set to `true`,
   * the isolate will start up in a paused state,
   * just before calling the [entryPoint] function with the [message],
   * as if by an initial call of `isolate.pause(isolate.pauseCapability)`.
   * To resume the isolate, call `isolate.resume(isolate.pauseCapability)`.
   *
   * If the [errorAreFatal], [onExit] and/or [onError] parameters are provided,
   * the isolate will act as if, respectively, [setErrorsFatal],
   * [addOnExitListener] and [addErrorListener] were called with the
   * corresponding parameter and was processed before the isolate starts
   * running.
   *
   * If [errorsAreFatal] is omitted, the platform may choose a default behavior
   * or inherit the current isolate's behavior.
   *
   * You can also call the [setErrorsFatal], [addOnExitListener] and
   * [addErrorListener] methods on the returned isolate, but unless the
   * isolate was started as [paused], it may already have terminated
   * before those methods can complete.
   *
   * Returns a future which will complete with an [Isolate] instance if the
   * spawning succeeded. It will complete with an error otherwise.
   */
  static Future<Isolate> spawn(void entryPoint(message), var message,
      {bool paused: false,
      bool errorsAreFatal,
      SendPort onExit,
      SendPort onError}) async {
    // `paused` isn't handled yet.
    RawReceivePort readyPort;
    try {
      // Check for the type of `entryPoint` on the spawning isolate to make
      // error-handling easier.
      if (entryPoint is! _UnaryFunction) {
        throw new ArgumentError(entryPoint);
      }
      // The VM will invoke [_startIsolate] with entryPoint as argument.
      readyPort = new RawReceivePort();

      // We do not inherit the package root or package config settings
      // from the parent isolate, instead we use the values that were
      // set on the command line.
      var packageRoot = VMLibraryHooks.packageRootString;
      var packageConfig = VMLibraryHooks.packageConfigString;
      var script = VMLibraryHooks.platformScript;
      if (script == null) {
        // We do not have enough information to support spawning the new
        // isolate.
        throw new UnsupportedError("Isolate.spawn");
      }
      if (script.scheme == "package") {
        script = await Isolate.resolvePackageUri(script);
      }

      _spawnFunction(readyPort.sendPort, script.toString(), entryPoint, message,
          paused, errorsAreFatal, onExit, onError, packageRoot, packageConfig);
      return await _spawnCommon(readyPort);
    } catch (e, st) {
      if (readyPort != null) {
        readyPort.close();
      }
      return await new Future<Isolate>.error(e, st);
    }
  }

  /**
   * Creates and spawns an isolate that runs the code from the library with
   * the specified URI.
   *
   * The isolate starts executing the top-level `main` function of the library
   * with the given URI.
   *
   * The target `main` must be callable with zero, one or two arguments.
   * Examples:
   *
   * * `main()`
   * * `main(args)`
   * * `main(args, message)`
   *
   * When present, the parameter `args` is set to the provided [args] list.
   * When present, the parameter `message` is set to the initial [message].
   *
   * If the [paused] parameter is set to `true`,
   * the isolate will start up in a paused state,
   * as if by an initial call of `isolate.pause(isolate.pauseCapability)`.
   * To resume the isolate, call `isolate.resume(isolate.pauseCapability)`.
   *
   * If the [errorAreFatal], [onExit] and/or [onError] parameters are provided,
   * the isolate will act as if, respectively, [setErrorsFatal],
   * [addOnExitListener] and [addErrorListener] were called with the
   * corresponding parameter and was processed before the isolate starts
   * running.
   *
   * You can also call the [setErrorsFatal], [addOnExitListener] and
   * [addErrorListener] methods on the returned isolate, but unless the
   * isolate was started as [paused], it may already have terminated
   * before those methods can complete.
   *
   * If the [checked] parameter is set to `true` or `false`,
   * the new isolate will run code in checked mode,
   * respectively in production mode, if possible.
   * If the parameter is omitted, the new isolate will inherit the
   * value from the current isolate.
   *
   * It may not always be possible to honor the `checked` parameter.
   * If the isolate code was pre-compiled, it may not be possible to change
   * the checked mode setting dynamically.
   * In that case, the `checked` parameter is ignored.
   *
   * WARNING: The [checked] parameter is not implemented on all platforms yet.
   *
   * If the [packageRoot] parameter is provided, it is used to find the location
   * of package sources in the spawned isolate.
   *
   * The `packageRoot` URI must be a "file" or "http"/"https" URI that specifies
   * a directory. If it doesn't end in a slash, one will be added before
   * using the URI, and any query or fragment parts are ignored.
   * Package imports (like `"package:foo/bar.dart"`) in the new isolate are
   * resolved against this location, as by
   * `packageRoot.resolve("foo/bar.dart")`.
   *
   * If the [packageConfig] parameter is provided, then it is used to find the
   * location of a package resolution configuration file for the spawned
   * isolate.
   *
   * If the [automaticPackageResolution] parameter is provided, then the
   * location of the package sources in the spawned isolate is automatically
   * determined.
   *
   * The [environment] is a mapping from strings to strings which the
   * spawned isolate uses when looking up [String.fromEnvironment] values.
   * The system may add its own entries to environment as well.
   * If `environment` is omitted, the spawned isolate has the same environment
   * declarations as the spawning isolate.
   *
   * WARNING: The [environment] parameter is not implemented on all
   * platforms yet.
   *
   * Returns a future that will complete with an [Isolate] instance if the
   * spawning succeeded. It will complete with an error otherwise.
   */
  static Future<Isolate> spawnUri(Uri uri, List<String> args, var message,
      {bool paused: false,
      SendPort onExit,
      SendPort onError,
      bool errorsAreFatal,
      bool checked,
      Map<String, String> environment,
      Uri packageRoot,
      Uri packageConfig,
      bool automaticPackageResolution: false}) async {
    RawReceivePort readyPort;
    if (environment != null) {
      throw new UnimplementedError("environment");
    }

    // Verify that no mutually exclusive arguments have been passed.
    if (automaticPackageResolution) {
      if (packageRoot != null) {
        throw new ArgumentError("Cannot simultaneously request "
            "automaticPackageResolution and specify a"
            "packageRoot.");
      }
      if (packageConfig != null) {
        throw new ArgumentError("Cannot simultaneously request "
            "automaticPackageResolution and specify a"
            "packageConfig.");
      }
    } else {
      if ((packageRoot != null) && (packageConfig != null)) {
        throw new ArgumentError("Cannot simultaneously specify a "
            "packageRoot and a packageConfig.");
      }
    }
    try {
      // Resolve the uri against the current isolate's root Uri first.
      var spawnedUri = _rootUri.resolveUri(uri);

      // Inherit this isolate's package resolution setup if not overridden.
      if (!automaticPackageResolution &&
          (packageRoot == null) &&
          (packageConfig == null)) {
        if (Isolate._packageSupported()) {
          packageRoot = await Isolate.packageRoot;
          packageConfig = await Isolate.packageConfig;
        }
      }

      // Ensure to resolve package: URIs being handed in as parameters.
      if (packageRoot != null) {
        // Avoid calling resolvePackageUri if not stricly necessary in case
        // the API is not supported.
        if (packageRoot.scheme == "package") {
          packageRoot = await Isolate.resolvePackageUri(packageRoot);
        }
      } else if (packageConfig != null) {
        // Avoid calling resolvePackageUri if not strictly necessary in case
        // the API is not supported.
        if (packageConfig.scheme == "package") {
          packageConfig = await Isolate.resolvePackageUri(packageConfig);
        }
      }

      // The VM will invoke [_startIsolate] and not `main`.
      readyPort = new RawReceivePort();
      var packageRootString = packageRoot?.toString();
      var packageConfigString = packageConfig?.toString();

      _spawnUri(
          readyPort.sendPort,
          spawnedUri.toString(),
          args,
          message,
          paused,
          onExit,
          onError,
          errorsAreFatal,
          checked,
          null,
          /* environment */
          packageRootString,
          packageConfigString);
      return await _spawnCommon(readyPort);
    } catch (e, st) {
      if (readyPort != null) {
        readyPort.close();
      }
      rethrow;
    }
  }

  /**
   * Requests the isolate to pause.
   *
   * When the isolate receives the pause command, it stops
   * processing events from the event loop queue.
   * It may still add new events to the queue in response to, e.g., timers
   * or receive-port messages. When the isolate is resumed,
   * it starts handling the already enqueued events.
   *
   * The pause request is sent through the isolate's command port,
   * which bypasses the receiving isolate's event loop.
   * The pause takes effect when it is received, pausing the event loop
   * as it is at that time.
   *
   * The [resumeCapability] is used to identity the pause,
   * and must be used again to end the pause using [resume].
   * If [resumeCapability] is omitted, a new capability object is created
   * and used instead.
   *
   * If an isolate is paused more than once using the same capability,
   * only one resume with that capability is needed to end the pause.
   *
   * If an isolate is paused using more than one capability,
   * each pause must be individually ended before the isolate resumes.
   *
   * Returns the capability that must be used to end the pause.
   * This is either [resumeCapability], or a new capability when
   * [resumeCapability] is omitted.
   *
   * If [pauseCapability] is `null`, or it's not the pause capability
   * of the isolate identified by [controlPort],
   * the pause request is ignored by the receiving isolate.
   */
  Capability pause([Capability resumeCapability]) {
    resumeCapability ??= new Capability();
    _pause(resumeCapability);
    return resumeCapability;
  }

  /** Internal implementation of [pause]. */
  void _pause(Capability resumeCapability) {
    var msg = new List(4)
      ..[0] = 0 // Make room for OOB message type.
      ..[1] = _PAUSE
      ..[2] = pauseCapability
      ..[3] = resumeCapability;
    _sendOOB(controlPort, msg);
  }

  /**
   * Resumes a paused isolate.
   *
   * Sends a message to an isolate requesting that it ends a pause
   * that was previously requested.
   *
   * When all active pause requests have been cancelled, the isolate
   * will continue processing events and handling normal messages.
   *
   * If the [resumeCapability] is not one that has previously been used
   * to pause the isolate, or it has already been used to resume from
   * that pause, the resume call has no effect.
   */
  void resume(Capability resumeCapability) {
    var msg = new List(4)
      ..[0] = 0 // Make room for OOB message type.
      ..[1] = _RESUME
      ..[2] = pauseCapability
      ..[3] = resumeCapability;
    _sendOOB(controlPort, msg);
  }

  /**
   * Requests an exist message on [responsePort] when the isolate terminates.
   *
   * The isolate will send [response] as a message on [responsePort] as the last
   * thing before it terminates. It will run no further code after the message
   * has been sent.
   *
   * Adding the same port more than once will only cause it to receive one exit
   * message, using the last response value that was added,
   * and it only needs to be removed once using [removeOnExitListener].
   *
   * If the isolate has terminated before it can receive this request,
   * no exit message will be sent.
   *
   * The [response] object must follow the same restrictions as enforced by
   * [SendPort.send].
   * It is recommended to only use simple values that can be sent to all
   * isolates, like `null`, booleans, numbers or strings.
   *
   * Since isolates run concurrently, it's possible for it to exit before the
   * exit listener is established, and in that case no response will be
   * sent on [responsePort].
   * To avoid this, either use the corresponding parameter to the spawn
   * function, or start the isolate paused, add the listener and
   * then resume the isolate.
   */
  /* TODO(lrn): Can we do better? Can the system recognize this message and
   * send a reply if the receiving isolate is dead?
   */
  void addOnExitListener(SendPort responsePort, {Object response}) {
    var msg = new List(4)
      ..[0] = 0 // Make room for OOB message type.
      ..[1] = _ADD_EXIT
      ..[2] = responsePort
      ..[3] = response;
    _sendOOB(controlPort, msg);
  }

  /**
   * Stop listening for exit messages from the isolate.
   *
   * Requests for the isolate to not send exit messages on [responsePort].
   * If the isolate isn't expecting to send exit messages on [responsePort],
   * because the port hasn't been added using [addOnExitListener],
   * or because it has already been removed, the request is ignored.
   *
   * If the same port has been passed via [addOnExitListener] more than once,
   * only one call to `removeOnExitListener` is needed to stop it from receiving
   * exit messagees.
   *
   * Closing the receive port at the end of the send port will not stop the
   * isolate from sending exit messages, they are just going to be lost.
   *
   * An exit message may still be sent if the isolate terminates
   * before this request is received and processed.
   */
  void removeOnExitListener(SendPort responsePort) {
    var msg = new List(3)
      ..[0] = 0 // Make room for OOB message type.
      ..[1] = _DEL_EXIT
      ..[2] = responsePort;
    _sendOOB(controlPort, msg);
  }

  /**
   * Set whether uncaught errors will terminate the isolate.
   *
   * If errors are fatal, any uncaught error will terminate the isolate
   * event loop and shut down the isolate.
   *
   * This call requires the [terminateCapability] for the isolate.
   * If the capability is absent or incorrect, no change is made.
   *
   * Since isolates run concurrently, it's possible for it to exit due to an
   * error before errors are set non-fatal.
   * To avoid this, either use the corresponding parameter to the spawn
   * function, or start the isolate paused, set errors non-fatal and
   * then resume the isolate.
   */
  void setErrorsFatal(bool errorsAreFatal) {
    var msg = new List(4)
      ..[0] = 0 // Make room for OOB message type.
      ..[1] = _ERROR_FATAL
      ..[2] = terminateCapability
      ..[3] = errorsAreFatal;
    _sendOOB(controlPort, msg);
  }

  /**
   * Requests the isolate to shut down.
   *
   * The isolate is requested to terminate itself.
   * The [priority] argument specifies when this must happen.
   *
   * The [priority], when provided, must be one of [IMMEDIATE] or
   * [BEFORE_NEXT_EVENT] (the default).
   * The shutdown is performed at different times depending on the priority:
   *
   * * `IMMEDIATE`: The isolate shuts down as soon as possible.
   *     Control messages are handled in order, so all previously sent control
   *     events from this isolate will all have been processed.
   *     The shutdown should happen no later than if sent with
   *     `BEFORE_NEXT_EVENT`.
   *     It may happen earlier if the system has a way to shut down cleanly
   *     at an earlier time, even during the execution of another event.
   * * `BEFORE_NEXT_EVENT`: The shutdown is scheduled for the next time
   *     control returns to the event loop of the receiving isolate,
   *     after the current event, and any already scheduled control events,
   *     are completed.
   *
   * If [terminateCapability] is `null`, or it's not the terminate capability
   * of the isolate identified by [controlPort],
   * the kill request is ignored by the receiving isolate.
   */
  void kill({int priority: BEFORE_NEXT_EVENT}) {
    var msg = new List(4)
      ..[0] = 0 // Make room for OOB message type.
      ..[1] = _KILL
      ..[2] = terminateCapability
      ..[3] = priority;
    _sendOOB(controlPort, msg);
  }

  /**
   * Request that the isolate send [response] on the [responsePort].
   *
   * The [response] object must follow the same restrictions as enforced by
   * [SendPort.send].
   * It is recommended to only use simple values that can be sent to all
   * isolates, like `null`, booleans, numbers or strings.
   *
   * If the isolate is alive, it will eventually send `response`
   * (defaulting to `null`) on the response port.
   *
   * The [priority] must be one of [IMMEDIATE] or [BEFORE_NEXT_EVENT].
   * The response is sent at different times depending on the ping type:
   *
   * * `IMMEDIATE`: The isolate responds as soon as it receives the
   *     control message. This is after any previous control message
   *     from the same isolate has been received and processed,
   *     but may be during execution of another event.
   * * `BEFORE_NEXT_EVENT`: The response is scheduled for the next time
   *     control returns to the event loop of the receiving isolate,
   *     after the current event, and any already scheduled control events,
   *     are completed.
   */
  void ping(SendPort responsePort, {Object response, int priority: IMMEDIATE}) {
    var msg = new List(5)
      ..[0] = 0 // Make room for OOM message type.
      ..[1] = _PING
      ..[2] = responsePort
      ..[3] = priority
      ..[4] = response;
    _sendOOB(controlPort, msg);
  }

  /**
   * Requests that uncaught errors of the isolate are sent back to [port].
   *
   * The errors are sent back as two elements lists.
   * The first element is a `String` representation of the error, usually
   * created by calling `toString` on the error.
   * The second element is a `String` representation of an accompanying
   * stack trace, or `null` if no stack trace was provided.
   * To convert this back to a [StackTrace] object, use [StackTrace.fromString].
   *
   * Listening using the same port more than once does nothing.
   * A port will only receive each error once,
   * and will only need to be removed once using [removeErrorListener].
   *
   * Since isolates run concurrently, it's possible for it to exit before the
   * error listener is established. To avoid this, start the isolate paused,
   * add the listener and then resume the isolate.
   */
  void addErrorListener(SendPort port) {
    var msg = new List(3)
      ..[0] = 0 // Make room for OOB message type.
      ..[1] = _ADD_ERROR
      ..[2] = port;
    _sendOOB(controlPort, msg);
  }

  /**
   * Stop listening for uncaught errors from the isolate.
   *
   * Requests for the isolate to not send uncaught errors on [responsePort].
   * If the isolate isn't expecting to send uncaught errors on [responsePort],
   * because the port hasn't been added using [addErrorListener],
   * or because it has already been removed, the request is ignored.
   *
   * If the same port has been passed via [addErrorListener] more than once,
   * only one call to `removeErrorListener` is needed to stop it from receiving
   * unaught errors.
   *
   * Closing the receive port at the end of the send port will not stop the
   * isolate from sending uncaught errors, they are just going to be lost.
   *
   * Uncaught errors message may still be sent by the isolate
   * until this request is received and processed.
   */
  void removeErrorListener(SendPort port) {
    var msg = new List(3)
      ..[0] = 0 // Make room for OOB message type.
      ..[1] = _DEL_ERROR
      ..[2] = port;
    _sendOOB(controlPort, msg);
  }

  /**
   * Returns a broadcast stream of uncaught errors from the isolate.
   *
   * Each error is provided as an error event on the stream.
   *
   * The actual error object and stackTraces will not necessarily
   * be the same object types as in the actual isolate, but they will
   * always have the same [Object.toString] result.
   *
   * This stream is based on [addErrorListener] and [removeErrorListener].
   */
  Stream get errors {
    StreamController controller;
    RawReceivePort port;
    void handleError(message) {
      String errorDescription = message[0];
      String stackDescription = message[1];
      var error = new RemoteError(errorDescription, stackDescription);
      controller.addError(error, error.stackTrace);
    }

    controller = new StreamController.broadcast(
        sync: true,
        onListen: () {
          port = new RawReceivePort(handleError);
          this.addErrorListener(port.sendPort);
        },
        onCancel: () {
          this.removeErrorListener(port.sendPort);
          port.close();
          port = null;
        });
    return controller.stream;
  }

  static const _PAUSE = 1;

  static Future<Isolate> _spawnCommon(RawReceivePort readyPort) {
    Completer completer = new Completer<Isolate>.sync();
    readyPort.handler = (readyMessage) {
      readyPort.close();
      if (readyMessage is List && readyMessage.length == 2) {
        SendPort controlPort = readyMessage[0];
        List capabilities = readyMessage[1];
        completer.complete(new Isolate(controlPort,
            pauseCapability: capabilities[0],
            terminateCapability: capabilities[1]));
      } else if (readyMessage is String) {
        // We encountered an error while starting the new isolate.
        completer.completeError(new IsolateSpawnException(
            'Unable to spawn isolate: ${readyMessage}'));
      } else {
        // This shouldn't happen.
        completer.completeError(new IsolateSpawnException(
            "Internal error: unexpected format for ready message: "
            "'${readyMessage}'"));
      }
    };
    return completer.future;
  }

  static final _currentIsolate = _getCurrentIsolate();

  static const _RESUME = 2;

  static const _PING = 3;

  static const _KILL = 4;

  static const _ADD_EXIT = 5;

  static const _DEL_EXIT = 6;

  static const _ADD_ERROR = 7;

  static const _DEL_ERROR = 8;

  static const _ERROR_FATAL = 9;

  static void _spawnFunction(
      SendPort readyPort,
      String uri,
      Function topLevelFunction,
      var message,
      bool paused,
      bool errorsAreFatal,
      SendPort onExit,
      SendPort onError,
      String packageRoot,
      String packageConfig) native "Isolate_spawnFunction";

  static void _spawnUri(
      SendPort readyPort,
      String uri,
      List<String> args,
      var message,
      bool paused,
      SendPort onExit,
      SendPort onError,
      bool errorsAreFatal,
      bool checked,
      List environment,
      String packageRoot,
      String packageConfig) native "Isolate_spawnUri";

  static void _sendOOB(port, msg) native "Isolate_sendOOB";

  static Isolate _getCurrentIsolate() {
    List portAndCapabilities = _getPortAndCapabilitiesOfCurrentIsolate();
    return new Isolate(portAndCapabilities[0],
        pauseCapability: portAndCapabilities[1],
        terminateCapability: portAndCapabilities[2]);
  }

  static List _getPortAndCapabilitiesOfCurrentIsolate()
      native "Isolate_getPortAndCapabilitiesOfCurrentIsolate";

  static Uri _getCurrentRootUri() {
    try {
      return Uri.parse(_getCurrentRootUriStr());
    } catch (e, s) {
      return null;
    }
  }

  static String _getCurrentRootUriStr() native "Isolate_getCurrentRootUriStr";

  static final _rootUri = _getCurrentRootUri();

  static bool _packageSupported() =>
      (VMLibraryHooks.packageRootUriFuture != null) &&
      (VMLibraryHooks.packageConfigUriFuture != null) &&
      (VMLibraryHooks.resolvePackageUriFuture != null);
}

/**
 * Sends messages to its [ReceivePort]s.
 *
 * [SendPort]s are created from [ReceivePort]s. Any message sent through
 * a [SendPort] is delivered to its corresponding [ReceivePort]. There might be
 * many [SendPort]s for the same [ReceivePort].
 *
 * [SendPort]s can be transmitted to other isolates, and they preserve equality
 * when sent.
 */
abstract class SendPort implements Capability {
  /**
   * Sends an asynchronous [message] through this send port, to its
   * corresponding `ReceivePort`.
   *
   * The content of [message] can be: primitive values (null, num, bool, double,
   * String), instances of [SendPort], and lists and maps whose elements are any
   * of these. List and maps are also allowed to be cyclic.
   *
   * In the special circumstances when two isolates share the same code and are
   * running in the same process (e.g. isolates created via [Isolate.spawn]), it
   * is also possible to send object instances (which would be copied in the
   * process). This is currently only supported by the dartvm.  For now, the
   * dart2js compiler only supports the restricted messages described above.
   *
   * The send happens immediately and doesn't block.  The corresponding receive
   * port can receive the message as soon as its isolate's event loop is ready
   * to deliver it, independently of what the sending isolate is doing.
   */
  void send(var message);

  /**
   * Tests whether [other] is a [SendPort] pointing to the same
   * [ReceivePort] as this one.
   */
  bool operator ==(var other);

  /**
   * Returns an immutable hash code for this send port that is
   * consistent with the == operator.
   */
  int get hashCode;
}

/**
 * Together with [SendPort], the only means of communication between isolates.
 *
 * [ReceivePort]s have a `sendPort` getter which returns a [SendPort].
 * Any message that is sent through this [SendPort]
 * is delivered to the [ReceivePort] it has been created from. There, the
 * message is dispatched to the `ReceivePort`'s listener.
 *
 * A [ReceivePort] is a non-broadcast stream. This means that it buffers
 * incoming messages until a listener is registered. Only one listener can
 * receive messages. See [Stream.asBroadcastStream] for transforming the port
 * to a broadcast stream.
 *
 * A [ReceivePort] may have many [SendPort]s.
 */
abstract class ReceivePort implements Stream {
  /**
   * Opens a long-lived port for receiving messages.
   *
   * A [ReceivePort] is a non-broadcast stream. This means that it buffers
   * incoming messages until a listener is registered. Only one listener can
   * receive messages. See [Stream.asBroadcastStream] for transforming the port
   * to a broadcast stream.
   *
   * A receive port is closed by canceling its subscription.
   */
  factory ReceivePort() = _ReceivePortImpl;

  /**
   * Creates a [ReceivePort] from a [RawReceivePort].
   *
   * The handler of the given [rawPort] is overwritten during the construction
   * of the result.
   */
  factory ReceivePort.fromRawReceivePort(RawReceivePort rawPort) =
      _ReceivePortImpl.fromRawReceivePort;

  /**
   * Inherited from [Stream].
   *
   * Note that [onError] and [cancelOnError] are ignored since a ReceivePort
   * will never receive an error.
   *
   * The [onDone] handler will be called when the stream closes.
   * The stream closes when [close] is called.
   */
  StreamSubscription listen(void onData(var message),
      {Function onError, void onDone(), bool cancelOnError});

  /**
   * Closes `this`.
   *
   * If the stream has not been canceled yet, adds a close-event to the event
   * queue and discards any further incoming messages.
   *
   * If the stream has already been canceled this method has no effect.
   */
  void close();

  /**
   * Returns a [SendPort] that sends to this receive port.
   */
  SendPort get sendPort;
}

abstract class RawReceivePort {
  /**
   * Opens a long-lived port for receiving messages.
   *
   * A [RawReceivePort] is low level and does not work with [Zone]s. It
   * can not be paused. The data-handler must be set before the first
   * event is received.
   */
  factory RawReceivePort([void handler(event)]) {
    _RawReceivePortImpl result = new _RawReceivePortImpl();
    result.handler = handler;
    return result;
  }

  /**
   * Sets the handler that is invoked for every incoming message.
   *
   * The handler is invoked in the root-zone ([Zone.ROOT]).
   */
  void set handler(Function newHandler);

  /**
   * Closes the port.
   *
   * After a call to this method any incoming message is silently dropped.
   */
  void close();

  /**
   * Returns a [SendPort] that sends to this raw receive port.
   */
  SendPort get sendPort;
}

/**
 * Description of an error from another isolate.
 *
 * This error has the same `toString()` and `stackTrace.toString()` behavior
 * as the original error, but has no other features of the original error.
 */
class RemoteError implements Error {
  final String _description;
  final StackTrace stackTrace;
  RemoteError(String description, String stackDescription)
      : _description = description,
        stackTrace = new StackTrace.fromString(stackDescription);
  String toString() => _description;
}

class _CapabilityImpl implements Capability {
  factory _CapabilityImpl() native "CapabilityImpl_factory";

  bool operator ==(var other) {
    return (other is _CapabilityImpl) && _equals(other);
  }

  int get hashCode {
    return _get_hashcode();
  }

  _equals(other) native "CapabilityImpl_equals";
  _get_hashcode() native "CapabilityImpl_get_hashcode";
}
class _ReceivePortImpl extends Stream implements ReceivePort {
  _ReceivePortImpl() : this.fromRawReceivePort(new RawReceivePort());

  _ReceivePortImpl.fromRawReceivePort(this._rawPort) {
    _controller = new StreamController(onCancel: close, sync: true);
    _rawPort.handler = _controller.add;
  }

  SendPort get sendPort {
    return _rawPort.sendPort;
  }

  StreamSubscription listen(void onData(var message),
      {Function onError, void onDone(), bool cancelOnError}) {
    return _controller.stream.listen(onData,
        onError: onError, onDone: onDone, cancelOnError: cancelOnError);
  }

  close() {
    _rawPort.close();
    _controller.close();
  }

  final RawReceivePort _rawPort;
  StreamController _controller;
}
typedef void _ImmediateCallback();
/// The callback that has been registered through `scheduleImmediate`.
_ImmediateCallback _pendingImmediateCallback;
/// The closure that should be used as scheduleImmediateClosure, when the VM
/// is responsible for the event loop.
void _isolateScheduleImmediate(void callback()) {
  assert(_pendingImmediateCallback == null);
  _pendingImmediateCallback = callback;
}
void _runPendingImmediateCallback() {
  if (_pendingImmediateCallback != null) {
    var callback = _pendingImmediateCallback;
    _pendingImmediateCallback = null;
    callback();
  }
}
_ImmediateCallback _removePendingImmediateCallback() {
  var callback = _pendingImmediateCallback;
  _pendingImmediateCallback = null;
  return callback;
}
/// The embedder can execute this function to get hold of
/// [_isolateScheduleImmediate] above.
Function _getIsolateScheduleImmediateClosure() {
  return _isolateScheduleImmediate;
}
class _RawReceivePortImpl implements RawReceivePort {
  factory _RawReceivePortImpl() native "RawReceivePortImpl_factory";

  close() {
    // Close the port and remove it from the handler map.
    _handlerMap.remove(this._closeInternal());
  }

  SendPort get sendPort {
    return _get_sendport();
  }

  bool operator ==(var other) {
    return (other is _RawReceivePortImpl) &&
        (this._get_id() == other._get_id());
  }

  int get hashCode {
    return sendPort.hashCode;
  }

  /**** Internal implementation details ****/
  int _get_id() native "RawReceivePortImpl_get_id";
  SendPort _get_sendport() native "RawReceivePortImpl_get_sendport";

  // Called from the VM to retrieve the handler for a message.
  static _lookupHandler(int id) {
    var result = _handlerMap[id];
    return result;
  }

  // Called from the VM to dispatch to the handler.
  static void _handleMessage(Function handler, var message) {
    // TODO(floitsch): this relies on the fact that any exception aborts the
    // VM. Once we have non-fatal global exceptions we need to catch errors
    // so that we can run the immediate callbacks.
    handler(message);
    _runPendingImmediateCallback();
  }

  // Call into the VM to close the VM maintained mappings.
  int _closeInternal() native "RawReceivePortImpl_closeInternal";

  void set handler(Function value) {
    _handlerMap[this._get_id()] = value;
  }

  // TODO(iposva): Ideally keep this map in the VM.
  // id to handler mapping.
  static Map<int, Function> _initHandlerMap() {
    // TODO(18511): Workaround bad CheckSmi hoisting.
    return new HashMap<int, Function>();
  }

  static final Map<int, Function> _handlerMap = _initHandlerMap();
}
class _SendPortImpl implements SendPort {
  /*--- public interface ---*/
  void send(var message) {
    _sendInternal(message);
  }

  bool operator ==(var other) {
    return (other is _SendPortImpl) && (this._get_id() == other._get_id());
  }

  int get hashCode {
    return _get_hashcode();
  }

  /*--- private implementation ---*/
  _get_id() native "SendPortImpl_get_id";
  _get_hashcode() native "SendPortImpl_get_hashcode";

  // Forward the implementation of sending messages to the VM.
  void _sendInternal(var message) native "SendPortImpl_sendInternal_";
}
typedef _NullaryFunction();
typedef _UnaryFunction(args);
typedef _BinaryFunction(args, message);
/**
 * Takes the real entry point as argument and invokes it with the
 * initial message.  Defers execution of the entry point until the
 * isolate is in the message loop.
 */
void _startMainIsolate(Function entryPoint, List<String> args) {
  _startIsolate(
      null, // no parent port
      entryPoint,
      args,
      null, // no message
      true, // isSpawnUri
      null, // no control port
      null); // no capabilities
}
/**
 * Takes the real entry point as argument and invokes it with the initial
 * message.
 */
void _startIsolate(
    SendPort parentPort,
    Function entryPoint,
    List<String> args,
    var message,
    bool isSpawnUri,
    RawReceivePort controlPort,
    List capabilities) {
  // The control port (aka the main isolate port) does not handle any messages.
  if (controlPort != null) {
    controlPort.handler = (_) {}; // Nobody home on the control port.
  }

  if (parentPort != null) {
    // Build a message to our parent isolate providing access to the
    // current isolate's control port and capabilities.
    //
    // TODO(floitsch): Send an error message if we can't find the entry point.
    var readyMessage = new List(2);
    readyMessage[0] = controlPort.sendPort;
    readyMessage[1] = capabilities;

    // Out of an excess of paranoia we clear the capabilities from the
    // stack.  Not really necessary.
    capabilities = null;
    parentPort.send(readyMessage);
  }
  assert(capabilities == null);

  // Delay all user code handling to the next run of the message loop. This
  // allows us to intercept certain conditions in the event dispatch, such as
  // starting in paused state.
  RawReceivePort port = new RawReceivePort();
  port.handler = (_) {
    port.close();

    if (isSpawnUri) {
      if (entryPoint is _BinaryFunction) {
        entryPoint(args, message);
      } else if (entryPoint is _UnaryFunction) {
        entryPoint(args);
      } else {
        entryPoint();
      }
    } else {
      entryPoint(message);
    }
  };
  // Make sure the message handler is triggered.
  port.sendPort.send(null);
}
class _TimerHeap {
  List<_Timer> _list;
  int _used = 0;

  _TimerHeap([int initSize = 7]) : _list = new List<_Timer>(initSize);

  bool get isEmpty => _used == 0;

  _Timer get first => _list[0];

  bool isFirst(_Timer timer) => timer._indexOrNext == 0;

  void add(_Timer timer) {
    if (_used == _list.length) {
      _resize();
    }
    timer._indexOrNext = _used++;
    _list[timer._indexOrNext] = timer;
    _bubbleUp(timer);
  }

  _Timer removeFirst() {
    var f = first;
    remove(f);
    return f;
  }

  void remove(_Timer timer) {
    _used--;
    if (isEmpty) {
      _list[0] = null;
      timer._indexOrNext = null;
      return;
    }
    var last = _list[_used];
    if (!identical(last, timer)) {
      last._indexOrNext = timer._indexOrNext;
      _list[last._indexOrNext] = last;
      if (last._compareTo(timer) < 0) {
        _bubbleUp(last);
      } else {
        _bubbleDown(last);
      }
    }
    _list[_used] = null;
    timer._indexOrNext = null;
  }

  void _resize() {
    var newList = new List(_list.length * 2 + 1);
    newList.setRange(0, _used, _list);
    _list = newList;
  }

  void _bubbleUp(_Timer timer) {
    while (!isFirst(timer)) {
      Timer parent = _parent(timer);
      if (timer._compareTo(parent) < 0) {
        _swap(timer, parent);
      } else {
        break;
      }
    }
  }

  void _bubbleDown(_Timer timer) {
    while (true) {
      int leftIndex = _leftChildIndex(timer._indexOrNext);
      int rightIndex = _rightChildIndex(timer._indexOrNext);
      _Timer newest = timer;
      if (leftIndex < _used && _list[leftIndex]._compareTo(newest) < 0) {
        newest = _list[leftIndex];
      }
      if (rightIndex < _used && _list[rightIndex]._compareTo(newest) < 0) {
        newest = _list[rightIndex];
      }
      if (identical(newest, timer)) {
        // We are where we should be, break.
        break;
      }
      _swap(newest, timer);
    }
  }

  void _swap(_Timer first, _Timer second) {
    int tmp = first._indexOrNext;
    first._indexOrNext = second._indexOrNext;
    second._indexOrNext = tmp;
    _list[first._indexOrNext] = first;
    _list[second._indexOrNext] = second;
  }

  Timer _parent(_Timer timer) => _list[_parentIndex(timer._indexOrNext)];
  Timer _leftChild(_Timer timer) => _list[_leftChildIndex(timer._indexOrNext)];
  Timer _rightChild(_Timer timer) =>
      _list[_rightChildIndex(timer._indexOrNext)];

  static int _parentIndex(int index) => (index - 1) ~/ 2;
  static int _leftChildIndex(int index) => 2 * index + 1;
  static int _rightChildIndex(int index) => 2 * index + 2;
}
class _Timer implements Timer {
  // Cancels the timer in the event handler.
  static const _NO_TIMER = -1;

  // We distinguish what kind of message arrived based on the value being sent.
  static const _ZERO_EVENT = 1;
  static const _TIMEOUT_EVENT = null;

  // Timers are ordered by wakeup time. Timers with a timeout value of > 0 do
  // end up on the TimerHeap. Timers with a timeout of 0 are queued in a list.
  static _TimerHeap _heap = new _TimerHeap();
  static _Timer _firstZeroTimer;
  static _Timer _lastZeroTimer;

  // We use an id to be able to sort timers with the same expiration time.
  // ids are recycled after ID_MASK enqueues or when the timer queue is empty.
  static const _ID_MASK = 0x1fffffff;
  static int _idCount = 0;

  static RawReceivePort _receivePort;
  static SendPort _sendPort;
  static int _scheduledWakeupTime;

  static bool _handlingCallbacks = false;

  Function _callback; // Closure to call when timer fires. null if canceled.
  int _wakeupTime; // Expiration time.
  final int _milliSeconds; // Duration specified at creation.
  final bool _repeating; // Indicates periodic timers.
  var _indexOrNext; // Index if part of the TimerHeap, link otherwise.
  int _id; // Incrementing id to enable sorting of timers with same expiry.

  // Get the next available id. We accept collisions and reordering when the
  // _idCount overflows and the timers expire at the same millisecond.
  static int _nextId() {
    var result = _idCount;
    _idCount = (_idCount + 1) & _ID_MASK;
    return result;
  }

  _Timer._internal(
      this._callback, this._wakeupTime, this._milliSeconds, this._repeating)
      : _id = _nextId();

  static Timer _createTimer(
      void callback(Timer timer), int milliSeconds, bool repeating) {
    // Negative timeouts are treated as if 0 timeout.
    if (milliSeconds < 0) {
      milliSeconds = 0;
    }
    // Add one because DateTime.now() is assumed to round down
    // to nearest millisecond, not up, so that time + duration is before
    // duration milliseconds from now. Using microsecond timers like
    // Stopwatch allows detecting that the timer fires early.
    int now = VMLibraryHooks.timerMillisecondClock();
    int wakeupTime = (milliSeconds == 0) ? now : (now + 1 + milliSeconds);

    _Timer timer =
        new _Timer._internal(callback, wakeupTime, milliSeconds, repeating);
    // Enqueue this newly created timer in the appropriate structure and
    // notify if necessary.
    timer._enqueue();
    return timer;
  }

  factory _Timer(int milliSeconds, void callback(Timer timer)) {
    return _createTimer(callback, milliSeconds, false);
  }

  factory _Timer.periodic(int milliSeconds, void callback(Timer timer)) {
    return _createTimer(callback, milliSeconds, true);
  }

  bool get _isInHeap => _indexOrNext is int;

  int _compareTo(_Timer other) {
    int c = _wakeupTime - other._wakeupTime;
    if (c != 0) return c;
    return _id - other._id;
  }

  bool get isActive => _callback != null;

  // Cancels a set timer. The timer is removed from the timer heap if it is a
  // non-zero timer. Zero timers are kept in the list as they need to consume
  // the corresponding pending message.
  void cancel() {
    _callback = null;
    // Only heap timers are really removed. Zero timers need to consume their
    // corresponding wakeup message so they are left in the queue.
    if (!_isInHeap) return;
    bool update = _heap.isFirst(this);
    _heap.remove(this);
    if (update) {
      _notifyEventHandler();
    }
  }

  void _advanceWakeupTime() {
    // Recalculate the next wakeup time. For repeating timers with a 0 timeout
    // the next wakeup time is now.
    _id = _nextId();
    if (_milliSeconds > 0) {
      _wakeupTime += _milliSeconds;
    } else {
      _wakeupTime = VMLibraryHooks.timerMillisecondClock();
    }
  }

  // Adds a timer to the heap or timer list. Timers with the same wakeup time
  // are enqueued in order and notified in FIFO order.
  void _enqueue() {
    if (_milliSeconds == 0) {
      if (_firstZeroTimer == null) {
        _lastZeroTimer = this;
        _firstZeroTimer = this;
      } else {
        _lastZeroTimer._indexOrNext = this;
        _lastZeroTimer = this;
      }
      // Every zero timer gets its own event.
      _notifyZeroHandler();
    } else {
      _heap.add(this);
      if (_heap.isFirst(this)) {
        _notifyEventHandler();
      }
    }
  }

  // Enqeue one message for each zero timer. To be able to distinguish from
  // EventHandler messages we send a _ZERO_EVENT instead of a _TIMEOUT_EVENT.
  static void _notifyZeroHandler() {
    if (_sendPort == null) {
      _createTimerHandler();
    }
    _sendPort.send(_ZERO_EVENT);
  }

  // Handle the notification of a zero timer. Make sure to also execute non-zero
  // timers with a lower expiration time.
  static List _queueFromZeroEvent() {
    var pendingTimers = new List();
    assert(_firstZeroTimer != null);
    // Collect pending timers from the timer heap that have an expiration prior
    // to the currently notified zero timer.
    var timer;
    while (!_heap.isEmpty && (_heap.first._compareTo(_firstZeroTimer) < 0)) {
      timer = _heap.removeFirst();
      pendingTimers.add(timer);
    }
    // Append the first zero timer to the pending timers.
    timer = _firstZeroTimer;
    _firstZeroTimer = timer._indexOrNext;
    timer._indexOrNext = null;
    pendingTimers.add(timer);
    return pendingTimers;
  }

  static void _notifyEventHandler() {
    if (_handlingCallbacks) {
      // While we are already handling callbacks we will not notify the event
      // handler. _handleTimeout will call _notifyEventHandler once all pending
      // timers are processed.
      return;
    }

    // If there are no pending timers. Close down the receive port.
    if ((_firstZeroTimer == null) && _heap.isEmpty) {
      // No pending timers: Close the receive port and let the event handler
      // know.
      if (_sendPort != null) {
        _cancelWakeup();
        _shutdownTimerHandler();
      }
      return;
    } else if (_heap.isEmpty) {
      // Only zero timers are left. Cancel any scheduled wakeups.
      _cancelWakeup();
      return;
    }

    // Only send a message if the requested wakeup time differs from the
    // already scheduled wakeup time.
    var wakeupTime = _heap.first._wakeupTime;
    if ((_scheduledWakeupTime == null) ||
        (wakeupTime != _scheduledWakeupTime)) {
      _scheduleWakeup(wakeupTime);
    }
  }

  static List _queueFromTimeoutEvent() {
    var pendingTimers = new List();
    if (_firstZeroTimer != null) {
      // Collect pending timers from the timer heap that have an expiration
      // prior to the next zero timer.
      // By definition the first zero timer has been scheduled before the
      // current time, meaning all timers which are "less than" the first zero
      // timer are expired. The first zero timer will be dispatched when its
      // corresponding message is delivered.
      var timer;
      while (!_heap.isEmpty && (_heap.first._compareTo(_firstZeroTimer) < 0)) {
        timer = _heap.removeFirst();
        pendingTimers.add(timer);
      }
    } else {
      // Collect pending timers from the timer heap which have expired at this
      // time.
      var currentTime = VMLibraryHooks.timerMillisecondClock();
      var timer;
      while (!_heap.isEmpty && (_heap.first._wakeupTime <= currentTime)) {
        timer = _heap.removeFirst();
        pendingTimers.add(timer);
      }
    }
    return pendingTimers;
  }

  static void _runTimers(List pendingTimers) {
    // If there are no pending timers currently reset the id space before we
    // have a chance to enqueue new timers.
    if (_heap.isEmpty && (_firstZeroTimer == null)) {
      _idCount = 0;
    }

    // Fast exit if no pending timers.
    if (pendingTimers.length == 0) {
      return;
    }

    // Trigger all of the pending timers. New timers added as part of the
    // callbacks will be enqueued now and notified in the next spin at the
    // earliest.
    _handlingCallbacks = true;
    try {
      for (var i = 0; i < pendingTimers.length; i++) {
        // Next pending timer.
        var timer = pendingTimers[i];
        timer._indexOrNext = null;

        // One of the timers in the pending_timers list can cancel
        // one of the later timers which will set the callback to
        // null. Or the pending zero timer has been canceled earlier.
        if (timer._callback != null) {
          var callback = timer._callback;
          if (!timer._repeating) {
            // Mark timer as inactive.
            timer._callback = null;
          }
          callback(timer);
          // Re-insert repeating timer if not canceled.
          if (timer._repeating && (timer._callback != null)) {
            timer._advanceWakeupTime();
            timer._enqueue();
          }
          // Execute pending micro tasks.
          var immediateCallback = _removePendingImmediateCallback();
          if (immediateCallback != null) {
            immediateCallback();
          }
        }
      }
    } finally {
      _handlingCallbacks = false;
    }
  }

  static void _handleMessage(msg) {
    var pendingTimers;
    if (msg == _ZERO_EVENT) {
      pendingTimers = _queueFromZeroEvent();
      assert(pendingTimers.length > 0);
    } else {
      assert(msg == _TIMEOUT_EVENT);
      _scheduledWakeupTime = null; // Consumed the last scheduled wakeup now.
      pendingTimers = _queueFromTimeoutEvent();
    }
    _runTimers(pendingTimers);
    // Notify the event handler or shutdown the port if no more pending
    // timers are present.
    _notifyEventHandler();
  }

  // Tell the event handler to wake this isolate at a specific time.
  static void _scheduleWakeup(int wakeupTime) {
    if (_sendPort == null) {
      _createTimerHandler();
    }
    VMLibraryHooks.eventHandlerSendData(null, _sendPort, wakeupTime);
    _scheduledWakeupTime = wakeupTime;
  }

  // Cancel pending wakeups in the event handler.
  static void _cancelWakeup() {
    assert(_sendPort != null);
    VMLibraryHooks.eventHandlerSendData(null, _sendPort, _NO_TIMER);
    _scheduledWakeupTime = null;
  }

  // Create a receive port and register a message handler for the timer
  // events.
  static void _createTimerHandler() {
    assert(_receivePort == null);
    assert(_sendPort == null);
    _receivePort = new RawReceivePort(_handleMessage);
    _sendPort = _receivePort.sendPort;
    _scheduledWakeupTime = null;
  }

  static void _shutdownTimerHandler() {
    _receivePort.close();
    _receivePort = null;
    _sendPort = null;
    _scheduledWakeupTime = null;
  }

  // The Timer factory registered with the dart:async library by the embedder.
  static Timer _factory(
      int milliSeconds, void callback(Timer timer), bool repeating) {
    if (repeating) {
      return new _Timer.periodic(milliSeconds, callback);
    }
    return new _Timer(milliSeconds, callback);
  }
}
_setupHooks() {
  VMLibraryHooks.timerFactory = _Timer._factory;
}