SharedPointer.h

/*
 * Copyright (c) 2008-2014, Pedigree Developers
 *
 * Please see the CONTRIB file in the root of the source tree for a full
 * list of contributors.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
 
#ifndef SHAREDPOINTER_H
#define SHAREDPOINTER_H
 
#include "pedigree/kernel/processor/types.h"
#include "pedigree/kernel/utilities/utility.h"
 
template <class T>
class SharedPointer {
 public:
  SharedPointer();
 
  SharedPointer(T* ptr);
 
  SharedPointer(SharedPointer<T>&& other) noexcept;
 
  virtual ~SharedPointer();
 
  SharedPointer(const SharedPointer<T>& p);
 
  void reset();
  void reset(T* ptr);
 
  T* get() const;
 
  T* operator->() const;
 
  T& operator*() const;
 
  SharedPointer<T>& operator=(const SharedPointer<T>& p);
 
  SharedPointer<T>& operator=(SharedPointer<T>&& p) noexcept;
 
  explicit operator bool() const;
 
  bool unique() const;
 
  size_t refcount() const;
 
  template <class... Args>
  static SharedPointer<T> allocate(Args...);
 
  template <class... Args>
  static SharedPointer<T> tryAllocate(Args...);
 
  static SharedPointer<T> tryAdopt(T* ptr);
 
  bool operator==(const SharedPointer& p) const;
  bool operator!=(const SharedPointer& p) const;
  bool operator<(const SharedPointer& p) const;
  bool operator<=(const SharedPointer& p) const;
  bool operator>(const SharedPointer& p) const;
  bool operator>=(const SharedPointer& p) const;
 
 private:
  void release() noexcept;
 
  struct Control {
    T* ptr;
    size_t refcount;
  }* m_Control;
};
 
template <class T>
SharedPointer<T>::SharedPointer() : m_Control(0) {}
 
template <class T>
SharedPointer<T>::SharedPointer(T* ptr) : m_Control(0) {
  reset(ptr);
}
 
template <class T>
SharedPointer<T>::SharedPointer(SharedPointer<T>&& other) noexcept {
  m_Control = other.m_Control;
 
  other.m_Control = nullptr;
}
 
template <class T>
SharedPointer<T>::~SharedPointer() {
  release();
}
 
template <class T>
SharedPointer<T>::SharedPointer(const SharedPointer<T>& p) : m_Control(0) {
  if (p.m_Control) {
    __atomic_add_fetch(&p.m_Control->refcount, 1, __ATOMIC_SEQ_CST);
  }
 
  release();
 
  m_Control = p.m_Control;
}
 
template <class T>
void SharedPointer<T>::reset() {
  release();
}
 
template <class T>
void SharedPointer<T>::reset(T* ptr) {
  release();
 
  m_Control = new Control;
  m_Control->refcount = 1;
  m_Control->ptr = ptr;
}
 
template <class T>
T* SharedPointer<T>::get() const {
  if (!m_Control)
    return 0;
 
  return m_Control->ptr;
}
 
template <class T>
T* SharedPointer<T>::operator->() const {
  return get();
}
 
template <class T>
T& SharedPointer<T>::operator*() const {
  return *(get());
}
 
template <class T>
SharedPointer<T>& SharedPointer<T>::operator=(const SharedPointer<T>& p) {
  if (this == &p) {
    return *this;
  }
 
  // If the other is assigned, boost its refcount before we release. If it
  // happens that the other is in fact pointing to the same place, the counts
  // will not potentially drop to zero then back to one this way (causing a
  // bad pointer).
  if (p.m_Control) {
    __atomic_add_fetch(&p.m_Control->refcount, 1, __ATOMIC_SEQ_CST);
  }
 
  release();
 
  m_Control = p.m_Control;
 
  return *this;
}
 
template <class T>
SharedPointer<T>& SharedPointer<T>::operator=(SharedPointer<T>&& p) noexcept {
  release();
  m_Control = p.m_Control;
  p.m_Control = nullptr;
 
  return *this;
}
 
template <class T>
SharedPointer<T>::operator bool() const {
  return get() != 0;
}
 
template <class T>
bool SharedPointer<T>::unique() const {
  return refcount() == 1;
}
 
template <class T>
size_t SharedPointer<T>::refcount() const {
  if (!m_Control)
    return 0;
 
  return __atomic_load_n(&m_Control->refcount, __ATOMIC_SEQ_CST);
}
 
template <class T>
template <class... Args>
SharedPointer<T> SharedPointer<T>::allocate(Args... args) {
  SharedPointer<T> result;
  result.reset(new T(args...));
  return pedigree_std::move(result);
}
 
template <class T>
template <class... Args>
SharedPointer<T> SharedPointer<T>::tryAllocate(Args... args) {
  SharedPointer<T> result;
  result.m_Control = new Control{nullptr, 1};
  if (!result.m_Control)
    return result;
  // Enrol the control block before constructing T, so hosted exceptions also
  // release it without publishing a partially constructed shared object.
  result.m_Control->ptr = new T(args...);
  if (!result.m_Control->ptr)
    result.reset();
  return result;
}
 
template <class T>
SharedPointer<T> SharedPointer<T>::tryAdopt(T* ptr) {
  SharedPointer<T> result;
  if (!ptr)
    return result;
  result.m_Control = new Control{ptr, 1};
  if (!result.m_Control)
    delete ptr;
  return result;
}
 
template <class T>
void SharedPointer<T>::release() noexcept {
  if (!m_Control)
    return;
 
  size_t rc = __atomic_sub_fetch(&m_Control->refcount, 1, __ATOMIC_SEQ_CST);
  if (!rc) {
    delete m_Control->ptr;
    m_Control->ptr = 0;
 
    delete m_Control;
  }
 
  // We don't care about the control structure anymore. Someone else will
  // free it if we did not.
  m_Control = 0;
}
 
template <class T>
bool SharedPointer<T>::operator==(const SharedPointer& p) const {
  return get() == p.get();
}
 
template <class T>
bool SharedPointer<T>::operator!=(const SharedPointer& p) const {
  return get() != p.get();
}
 
template <class T>
bool SharedPointer<T>::operator<(const SharedPointer& p) const {
  return get() < p.get();
}
 
template <class T>
bool SharedPointer<T>::operator<=(const SharedPointer& p) const {
  return get() <= p.get();
}
 
template <class T>
bool SharedPointer<T>::operator>(const SharedPointer& p) const {
  return get() > p.get();
}
 
template <class T>
bool SharedPointer<T>::operator>=(const SharedPointer& p) const {
  return get() >= p.get();
}
 
#endif