Rework standalone to use a synchronous loader that does not invoke Dart code

runtime/bin/loader.h

+// Copyright (c) 2016, 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.
+
+#ifndef BIN_LOADER_H_
+#define BIN_LOADER_H_
+
+#include "bin/isolate_data.h"
+#include "include/dart_api.h"
+#include "include/dart_native_api.h"
+#include "platform/assert.h"
+#include "platform/globals.h"
+#include "bin/thread.h"
+
+namespace dart {
+namespace bin {
+
+class Loader {
+ public:
+  explicit Loader(IsolateData* isolate_data);
+  ~Loader();
+
+  // A static tag handler that hides all usage of a loader for an isolate.
+  static Dart_Handle LibraryTagHandler(Dart_LibraryTag tag,
+                                       Dart_Handle library,
+                                       Dart_Handle url);
+
+  Dart_Handle error() const {
+    return error_;
+  }
+
+ private:
+  // The port assigned to our native message handler.
+  Dart_Port port_;
+  // Each Loader is associated with an Isolate via its IsolateData.
+  IsolateData* isolate_data_;
+  // Remember the first error that occurs during loading.
+  Dart_Handle error_;
+
+  // This monitor is used to protect the pending operations count and the
+  // I/O result queue.
+  Monitor* monitor_;
+
+  // The number of operations dispatched to the service isolate for loading.
+  // Must be accessed with monitor_ held.
+  intptr_t pending_operations_;
+
+  // The result of an I/O request to the service isolate. Payload is either
+  // a UInt8Array or a C string containing an error message.
+  struct IOResult {
+    uint8_t* payload;
+    intptr_t payload_length;
+    char* library_uri;
+    char* uri;
+    int8_t tag;
+
+    void Setup(Dart_CObject* message);
+    void Cleanup();
+  };
+  // An array of I/O results queued from the service isolate.
+  IOResult* results_;
+  intptr_t results_length_;
+  intptr_t results_capacity_;
+
+  intptr_t results_length() {
+    return *static_cast<volatile intptr_t*>(&results_length_);
+  }
+
+  // Send the loader init request to the service isolate.
+  void Init(const char* package_root,
+            const char* packages_file,
+            const char* working_directory);
+
+  // Send a request from the tag handler to the service isolate.
+  void SendRequest(Dart_LibraryTag tag,
+                   Dart_Handle url,
+                   Dart_Handle library_url);
+
+  /// Queue |message| and notify the loader that a message is available.
+  void QueueMessage(Dart_CObject* message);
+
+  /// Blocks the caller until the loader is finished.
+  void BlockUntilComplete();
+
+  /// Returns false if |result| is an error and the loader should quit.
+  bool ProcessResultLocked(IOResult* result);
+
+  /// Returns false if an error occurred and the loader should quit.
+  bool ProcessQueueLocked();
+
+  // Special inner tag handler for dart: uris.
+  static Dart_Handle DartColonLibraryTagHandler(Dart_LibraryTag tag,
+                                                Dart_Handle library,
+                                                Dart_Handle url,
+                                                const char* library_url_string,
+                                                const char* url_string);
+
+  // We use one native message handler callback for N loaders. The native
+  // message handler callback provides us with the Dart_Port which we use as a
+  // key into our map of active loaders from |port| to |isolate_data|.
+
+  // Static information to map Dart_Port back to the isolate in question.
+  struct LoaderInfo {
+    Dart_Port port;
+    IsolateData* isolate_data;
+  };
+
+  // The map of active loaders.
+  static Mutex loader_infos_lock_;
+  static LoaderInfo* loader_infos_;
+  static intptr_t loader_infos_length_;
+  static intptr_t loader_infos_capacity_;
+
+  static void AddLoader(Dart_Port port, IsolateData* data);
+  static void RemoveLoader(Dart_Port port);
+  static intptr_t LoaderIndexFor(Dart_Port port);
+  static Loader* LoaderFor(Dart_Port port);
+
+  // This is the global callback for the native message handlers.
+  static void NativeMessageHandler(Dart_Port dest_port_id,
+                                   Dart_CObject* message);
+};
+
+}  // namespace bin
+}  // namespace dart
+
+#endif  // BIN_LOADER_H_