third_party/protobuf/3.6.1/python/google/protobuf/pyext/thread_unsafe_shared_ptr.h

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// ThreadUnsafeSharedPtr<T> is the same as shared_ptr<T> without the locking
// overhread (and thread-safety).
#ifndef GOOGLE_PROTOBUF_PYTHON_CPP_THREAD_UNSAFE_SHARED_PTR_H__
#define GOOGLE_PROTOBUF_PYTHON_CPP_THREAD_UNSAFE_SHARED_PTR_H__

#include <algorithm>
#include <utility>

#include <google/protobuf/stubs/logging.h>
#include <google/protobuf/stubs/common.h>

namespace google {
namespace protobuf {
namespace python {

template <typename T>
class ThreadUnsafeSharedPtr {
 public:
  // Takes ownership.
  explicit ThreadUnsafeSharedPtr(T* ptr)
      : ptr_(ptr), refcount_(ptr ? new RefcountT(1) : nullptr) {
  }

  ThreadUnsafeSharedPtr(const ThreadUnsafeSharedPtr& other)
      : ThreadUnsafeSharedPtr(nullptr) {
    *this = other;
  }

  ThreadUnsafeSharedPtr& operator=(const ThreadUnsafeSharedPtr& other) {
    if (other.refcount_ == refcount_) {
      return *this;
    }
    this->~ThreadUnsafeSharedPtr();
    ptr_ = other.ptr_;
    refcount_ = other.refcount_;
    if (refcount_) {
      ++*refcount_;
    }
    return *this;
  }

  ~ThreadUnsafeSharedPtr() {
    if (refcount_ == nullptr) {
      GOOGLE_DCHECK(ptr_ == nullptr);
      return;
    }
    if (--*refcount_ == 0) {
      delete refcount_;
      delete ptr_;
    }
  }

  void reset(T* ptr = nullptr) { *this = ThreadUnsafeSharedPtr(ptr); }

  T* get() { return ptr_; }
  const T* get() const { return ptr_; }

  void swap(ThreadUnsafeSharedPtr& other) {
    using std::swap;
    swap(ptr_, other.ptr_);
    swap(refcount_, other.refcount_);
  }

 private:
  typedef int RefcountT;
  T* ptr_;
  RefcountT* refcount_;
};

}  // namespace python
}  // namespace protobuf

}  // namespace google
#endif  // GOOGLE_PROTOBUF_PYTHON_CPP_THREAD_UNSAFE_SHARED_PTR_H__