api: introduce SealHandleScope

When debugging Handle leaks in io.js we found it very convenient to be
able to Seal some specific (root in our case) scope to prevent Handle
allocations in it, and easily find leakage.

R=yangguo
BUG=

Review URL: https://codereview.chromium.org/1079713002

Cr-Commit-Position: refs/heads/master@{#27766}

diff --git a/include/v8.h b/include/v8.h
index 8019a45..d94e9b3 100644 (file)
--- a/include/v8.h
+++ b/include/v8.h
@@ -1018,6 +1018,24 @@ class V8_EXPORT EscapableHandleScope : public HandleScope {
   internal::Object** escape_slot_;
 };
 
+class V8_EXPORT SealHandleScope {
+ public:
+  SealHandleScope(Isolate* isolate);
+  ~SealHandleScope();
+
+ private:
+  // Make it hard to create heap-allocated or illegal handle scopes by
+  // disallowing certain operations.
+  SealHandleScope(const SealHandleScope&);
+  void operator=(const SealHandleScope&);
+  void* operator new(size_t size);
+  void operator delete(void*, size_t);
+
+  internal::Isolate* isolate_;
+  int prev_level_;
+  internal::Object** prev_limit_;
+};
+
 
 // --- Special objects ---
 

diff --git a/src/api.cc b/src/api.cc
index 28c8410..733214e 100644 (file)
--- a/src/api.cc
+++ b/src/api.cc
@@ -674,6 +674,27 @@ i::Object** EscapableHandleScope::Escape(i::Object** escape_value) {
 }
 
 
+SealHandleScope::SealHandleScope(Isolate* isolate) {
+  i::Isolate* internal_isolate = reinterpret_cast<i::Isolate*>(isolate);
+
+  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();

diff --git a/src/api.h b/src/api.h
index fa8682b..7fce3e3 100644 (file)
--- a/src/api.h
+++ b/src/api.h
@@ -661,7 +661,7 @@ void HandleScopeImplementer::DeleteExtensions(internal::Object** prev_limit) {
   while (!blocks_.is_empty()) {
     internal::Object** block_start = blocks_.last();
     internal::Object** block_limit = block_start + kHandleBlockSize;
-#ifdef DEBUG
+
     // SealHandleScope may make the prev_limit to point inside the block.
     if (block_start <= prev_limit && prev_limit <= block_limit) {
 #ifdef ENABLE_HANDLE_ZAPPING
@@ -669,9 +669,6 @@ void HandleScopeImplementer::DeleteExtensions(internal::Object** prev_limit) {
 #endif
       break;
     }
-#else
-    if (prev_limit == block_limit) break;
-#endif
 
     blocks_.RemoveLast();
 #ifdef ENABLE_HANDLE_ZAPPING

diff --git a/test/cctest/cctest.status b/test/cctest/cctest.status
index 34cbab1..2fcf8a5 100644 (file)
--- a/test/cctest/cctest.status
+++ b/test/cctest/cctest.status
@@ -40,6 +40,7 @@
   # they don't fail then test.py has failed.
   'test-serialize/TestThatAlwaysFails': [FAIL],
   'test-serialize/DependentTestThatAlwaysFails': [FAIL],
+  'test-api/SealHandleScope': [FAIL],
 
   # This test always fails.  It tests that LiveEdit causes abort when turned off.
   'test-debug/LiveEditDisabled': [FAIL],

diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index f7cbb82..5f9612e 100644 (file)
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -21900,3 +21900,35 @@ TEST(NewStringRangeError) {
   }
   free(buffer);
 }
+
+
+TEST(SealHandleScope) {
+  v8::Isolate* isolate = CcTest::isolate();
+  v8::HandleScope handle_scope(isolate);
+  LocalContext env;
+
+  v8::SealHandleScope seal(isolate);
+
+  // Should fail
+  v8::Local<v8::Object> obj = v8::Object::New(isolate);
+
+  USE(obj);
+}
+
+
+TEST(SealHandleScopeNested) {
+  v8::Isolate* isolate = CcTest::isolate();
+  v8::HandleScope handle_scope(isolate);
+  LocalContext env;
+
+  v8::SealHandleScope seal(isolate);
+
+  {
+    v8::HandleScope handle_scope(isolate);
+
+    // Should work
+    v8::Local<v8::Object> obj = v8::Object::New(isolate);
+
+    USE(obj);
+  }
+}