src/hotspot/share/oops/oopHandle.hpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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#ifndef SHARE_OOPS_OOPHANDLE_HPP
#define SHARE_OOPS_OOPHANDLE_HPP

#include "metaprogramming/primitiveConversions.hpp"
#include "oops/oopsHierarchy.hpp"

#include <type_traits>

class OopStorage;

// Simple classes for wrapping oop and atomically accessed oop pointers
// stored in OopStorage, or stored in the ClassLoaderData handles area.
// These classes help with allocation, release, and NativeAccess loads and
// stores with the appropriate barriers.

class OopHandle {
  friend class VMStructs;
private:
  oop* _obj;

public:
  OopHandle() : _obj(nullptr) {}
  explicit OopHandle(oop* w) : _obj(w) {}
  OopHandle(OopStorage* storage, oop obj);

  OopHandle(const OopHandle& copy) : _obj(copy._obj) {}

  OopHandle& operator=(const OopHandle& copy) {
    // Allow "this" to be junk if copy is empty; needed by initialization of
    // raw memory in hashtables.
    assert(is_empty() || copy.is_empty(), "can only copy if empty");
    _obj = copy._obj;
    return *this;
  }

  void swap(OopHandle& copy) {
    ::swap(_obj, copy._obj);
  }

  inline oop resolve() const;
  inline oop peek() const;

  bool is_empty() const { return _obj == nullptr; }

  inline void release(OopStorage* storage);

  inline void replace(oop obj);

  inline oop xchg(oop new_value);

  oop* ptr_raw() const { return _obj; }
};

// Convert OopHandle to oop*

template<>
struct PrimitiveConversions::Translate<OopHandle> : public std::true_type {
  typedef OopHandle Value;
  typedef oop* Decayed;

  static Decayed decay(Value x) { return x.ptr_raw(); }
  static Value recover(Decayed x) { return OopHandle(x); }
};

#endif // SHARE_OOPS_OOPHANDLE_HPP