/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef jit_OffthreadSnapshot_h
#define jit_OffthreadSnapshot_h

#include "gc/Policy.h"
#include "gc/Tracer.h"

// Wrapper for GC things stored in snapshots for offthread compilation.
// Asserts the GC pointer is not nursery-allocated.
// These pointers must be traced using TraceOffthreadGCPtr.
template <typename T>
class OffthreadGCPtr {
  // Note: no pre-barrier is needed because after being initialized to a
  // non-empty OffthreadGCPtr this is a constant. No post-barrier is needed
  // because the value is always tenured.
  T ptr_ = JS::SafelyInitialized<T>::create();

 public:
  constexpr OffthreadGCPtr() = default;

  explicit OffthreadGCPtr(const T& ptr) : ptr_(ptr) {
    MOZ_ASSERT(JS::GCPolicy<T>::isTenured(ptr),
               "OffthreadSnapshot pointers must be tenured");
  }
  OffthreadGCPtr(const OffthreadGCPtr<T>& other) = default;

  operator T() const { return ptr_; }
  T operator->() const { return ptr_; }

  void init(T& ptr) {
    MOZ_ASSERT(JS::GCPolicy<T>::isTenured(ptr),
               "OffthreadSnapshot pointers must be tenured");
    MOZ_ASSERT(ptr_ == JS::SafelyInitialized<T>::create(),
               "init can only be called on empty OffthreadGCPtr");
    ptr_ = ptr;
  }

 private:
  void operator=(OffthreadGCPtr<T>& other) = delete;
};

template <typename T>
inline void TraceOffthreadGCPtr(JSTracer* trc, const OffthreadGCPtr<T>& thing,
                                const char* name) {
  T thingRaw = thing;
  js::TraceManuallyBarrieredEdge(trc, &thingRaw, name);
  MOZ_ASSERT(static_cast<T>(thing) == thingRaw, "Unexpected moving GC!");
}

#endif /* jit_OffthreadSnapshot_h */