Create read only handles for empty_array and sentinel objects

vm/dart.cc

 // 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.
 
 #include "vm/dart.h"
 
 #include "vm/code_observers.h"
 #include "vm/dart_api_state.h"
 #include "vm/flags.h"
 #include "vm/freelist.h"
@@ skipping 15 matching lines @@
 DEFINE_FLAG(bool, heap_profile_initialize, false,
             "Writes a heap profile on isolate initialization.");
 DECLARE_FLAG(bool, heap_trace);
 DECLARE_FLAG(bool, print_bootstrap);
 DECLARE_FLAG(bool, print_class_table);
 DECLARE_FLAG(bool, trace_isolates);
 
 Isolate* Dart::vm_isolate_ = NULL;
 ThreadPool* Dart::thread_pool_ = NULL;
 DebugInfo* Dart::pprof_symbol_generator_ = NULL;
+ReadOnlyHandles* Dart::predefined_handles_ = NULL;
 
 // An object visitor which will mark all visited objects. This is used to
 // premark all objects in the vm_isolate_ heap.
 class PremarkingVisitor : public ObjectVisitor {
  public:
   explicit PremarkingVisitor(Isolate* isolate) : ObjectVisitor(isolate) {}
 
   void VisitObject(RawObject* obj) {
     // RawInstruction objects are premarked on allocation.
     if (!obj->IsMarked()) {
       obj->SetMarkBit();
     }
   }
 };
 
 
+// Structure for managing read only global handles allocation used for
+// creating global read only handles that are pre created and initialized
+// for use across all isolates. Having these global pre created handles
+// stored in the vm isolate ensures that we don't constantly create and
+// destroy handles for read only objects referred in the VM code
+// (e.g: symbols, null object, empty array etc.

[Ivan Posva, 2012/12/20 23:43:52]

Maybe explain why this is wrapped in an object in itself and not just a static
VMHandles?

[siva, 2012/12/21 02:28:06]

Done.

+class ReadOnlyHandles {
+ public:
+  ReadOnlyHandles() { }
+
+ private:
+  VMHandles handles_;
+
+  friend class Dart;
+  DISALLOW_COPY_AND_ASSIGN(ReadOnlyHandles);
+};
+
+
 // TODO(turnidge): We should add a corresponding Dart::Cleanup.
 const char* Dart::InitOnce(Dart_IsolateCreateCallback create,
                            Dart_IsolateInterruptCallback interrupt,
                            Dart_IsolateUnhandledExceptionCallback unhandled,
                            Dart_IsolateShutdownCallback shutdown,
                            Dart_FileOpenCallback file_open,
                            Dart_FileWriteCallback file_write,
                            Dart_FileCloseCallback file_close) {
   // TODO(iposva): Fix race condition here.
   if (vm_isolate_ != NULL || !Flags::Initialized()) {
     return "VM already initialized.";
   }
   Isolate::SetFileCallbacks(file_open, file_write, file_close);
   OS::InitOnce();
   VirtualMemory::InitOnce();
   Isolate::InitOnce();
   PortMap::InitOnce();
   FreeListElement::InitOnce();
   Api::InitOnce();
   CodeObservers::InitOnce();
+  // Create the read only handles area.
+  ASSERT(predefined_handles_ == NULL);
+  predefined_handles_ = new ReadOnlyHandles();
   // Create the VM isolate and finish the VM initialization.
   ASSERT(thread_pool_ == NULL);
   thread_pool_ = new ThreadPool();
   {
     ASSERT(vm_isolate_ == NULL);
     ASSERT(Flags::Initialized());
     vm_isolate_ = Isolate::Init("vm-isolate");
     StackZone zone(vm_isolate_);
     HandleScope handle_scope(vm_isolate_);
     Heap::Init(vm_isolate_);
@@ skipping 121 matching lines @@
   isolate->Shutdown();
   delete isolate;
 
   Dart_IsolateShutdownCallback callback = Isolate::ShutdownCallback();
   if (callback != NULL) {
     (callback)(callback_data);
   }
 }
 
 
+uword Dart::AllocateReadOnlyHandle() {
+  ASSERT(predefined_handles_ != NULL);
+  return predefined_handles_->handles_.AllocateScopedHandle();
+}
+
+
+bool Dart::IsReadOnlyHandle(uword address) {
+  ASSERT(predefined_handles_ != NULL);
+  return predefined_handles_->handles_.IsValidScopedHandle(address);
+}
+
 }  // namespace dart