api: introduce SealHandleScope

src/api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 668 matching lines @@
                   "Escape value set twice");
   if (escape_value == NULL) {
     *escape_slot_ = heap->undefined_value();
     return NULL;
   }
   *escape_slot_ = *escape_value;
   return escape_slot_;
 }
 
 
+SealHandleScope::SealHandleScope(Isolate* isolate) {
+  i::Isolate* internal_isolate = reinterpret_cast<i::Isolate*>(isolate);
+  // We do not want to check the correct usage of the Locker class all over the
+  // place, so we do it only here: Without a HandleScope, an embedder can do
+  // almost nothing, so it is enough to check in this central place.
+  // We make an exception if the serializer is enabled, which means that the
+  // Isolate is exclusively used to create a snapshot.
+  Utils::ApiCheck(
+      !v8::Locker::IsActive() ||
+          internal_isolate->thread_manager()->IsLockedByCurrentThread() ||
+          internal_isolate->serializer_enabled(),
+      "SealHandleScope::SealHandleScope",
+      "Entering the V8 API without proper locking in place");

[Yang, 2015/03/13 07:18:20]

Do we actually need this check here? If you want to create a handle, what you
need is a HandleScope, which would check for locking. By having a
SealHandleScope, we would explicitly require a new HandleScope if someone wants
to create a handle.

+
+  isolate_ = internal_isolate;
+  i::HandleScopeData* current = internal_isolate->handle_scope_data();
+  prev_limit_ = current->limit;
+  current->limit = current->next;
+  prev_level_ = current->level;
+  current->level = 0;
+}
+
+
+SealHandleScope::~SealHandleScope() {
+  i::HandleScopeData* current = isolate_->handle_scope_data();
+  DCHECK_EQ(0, current->level);
+  current->level = prev_level_;
+  DCHECK_EQ(current->next, current->limit);
+  current->limit = prev_limit_;
+}
+
+
 void Context::Enter() {
   i::Handle<i::Context> env = Utils::OpenHandle(this);
   i::Isolate* isolate = env->GetIsolate();
   ENTER_V8(isolate);
   i::HandleScopeImplementer* impl = isolate->handle_scope_implementer();
   impl->EnterContext(env);
   impl->SaveContext(isolate->context());
   isolate->set_context(*env);
 }
 
@@ skipping 7299 matching lines @@
   Isolate* isolate = reinterpret_cast<Isolate*>(info.GetIsolate());
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 } }  // namespace v8::internal