BLI_shared_cache.hh

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

 
#pragma once
 
#include "BLI_cache_mutex.hh"
 
#include <memory>
 
namespace blender {

template<typename T> class SharedCache {
  struct CacheData {
    CacheMutex mutex;
    T data;
    CacheData() = default;
    CacheData(const T &data) : data(data) {}
  };
  std::shared_ptr<CacheData> cache_;
 
 public:
  SharedCache()
  {
    /* The cache should be allocated to trigger sharing of the cached data as early as possible. */
    cache_ = std::make_shared<CacheData>();
  }

  void tag_dirty()
  {
    if (cache_.use_count() == 1) {
      cache_->mutex.tag_dirty();
    }
    else {
      cache_ = std::make_shared<CacheData>();
    }
  }

  void ensure(FunctionRef<void(T &data)> compute_cache)
  {
    cache_->mutex.ensure([&]() { compute_cache(this->cache_->data); });
  }

  void update(FunctionRef<void(T &data)> compute_cache)
  {
    if (cache_.use_count() == 1) {
      cache_->mutex.tag_dirty();
    }
    else {
      cache_ = std::make_shared<CacheData>(cache_->data);
    }
    cache_->mutex.ensure([&]() { compute_cache(this->cache_->data); });
  }

  const T &data() const
  {
    BLI_assert(cache_->mutex.is_cached());
    return cache_->data;
  }

  bool is_dirty() const
  {
    return cache_->mutex.is_dirty();
  }

  bool is_cached() const
  {
    return cache_->mutex.is_cached();
  }
};
 
}  // namespace blender