[wasm] Managed<T> ensures T's lifetime does not leak past Isolate's

src/isolate.h

 // 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.
 
 #ifndef V8_ISOLATE_H_
 #define V8_ISOLATE_H_
 
 #include <memory>
 #include <queue>
 
@@ skipping 1182 matching lines @@
 
   PRINTF_FORMAT(2, 3) void PrintWithTimestamp(const char* format, ...);
 
 #ifdef USE_SIMULATOR
   base::Mutex* simulator_i_cache_mutex() { return &simulator_i_cache_mutex_; }
 #endif
 
   void set_allow_atomics_wait(bool set) { allow_atomics_wait_ = set; }
   bool allow_atomics_wait() { return allow_atomics_wait_; }
 
+  // List of native heap values allocated by the runtime as part of its
+  // implementation
+  // that must be freed at isolate deinit.
+  class ManagedLifeline final {

[titzer, 2017/02/08 23:32:47]

Please just make this a struct, forward declare it, and put it in the isolate.cc
file.

[titzer, 2017/02/08 23:32:48]

ManagedObjectList?

[Mircea Trofin, 2017/02/08 23:52:35]

Maybe - although the fact it's a list is an implementation detail to its
consumer. The consumer sees it as something that it can get a value from and can
be deleted. It's a handle, rather, but that term is something else in V8 :)

[Mircea Trofin, 2017/02/08 23:52:36]

The user of this needs to call the value() API (see managed.h, get()). 

+   public:
+    typedef void (*Deleter)(void*);
+    ~ManagedLifeline();
+    void* value() const { return value_; }
+
+   private:
+    friend class Isolate;
+
+    ManagedLifeline()
+        : prev_(nullptr), next_(nullptr), deleter_(nullptr), value_(nullptr) {}

[titzer, 2017/02/08 23:32:47]

I think you can use the inline initializer for these fields now.

[Mircea Trofin, 2017/02/08 23:52:36]

Acknowledged.

+    void Clear();
+    void CallDeleter();
+
+    ManagedLifeline* prev_;
+    ManagedLifeline* next_;
+    Deleter deleter_;
+    void* value_;
+  };
+
+  ManagedLifeline* AddManagedObject(void* value,
+                                    ManagedLifeline::Deleter deleter);
+
  protected:
   explicit Isolate(bool enable_serializer);
   bool IsArrayOrObjectPrototype(Object* object);
 
  private:
   friend struct GlobalState;
   friend struct InitializeGlobalState;
 
   // These fields are accessed through the API, offsets must be kept in sync
   // with v8::internal::Internals (in include/v8.h) constants. This is also
@@ skipping 261 matching lines @@
 
   v8::Isolate::AbortOnUncaughtExceptionCallback
       abort_on_uncaught_exception_callback_;
 
 #ifdef USE_SIMULATOR
   base::Mutex simulator_i_cache_mutex_;
 #endif
 
   bool allow_atomics_wait_;
 
+  ManagedLifeline managed_lifelines_root_;
+
   friend class ExecutionAccess;
   friend class HandleScopeImplementer;
   friend class HeapTester;
   friend class OptimizingCompileDispatcher;
   friend class SweeperThread;
   friend class ThreadManager;
   friend class Simulator;
   friend class StackGuard;
   friend class ThreadId;
   friend class v8::Isolate;
@@ skipping 216 matching lines @@
 
   EmbeddedVector<char, 128> filename_;
   FILE* file_;
   int scope_depth_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ISOLATE_H_