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// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/ledger/bin/app/types.h"
#include "src/ledger/bin/fidl/include/types.h"
#include "src/ledger/bin/storage/public/iterator.h"
#include "src/ledger/bin/storage/public/types.h"
#include "src/ledger/lib/coroutine/coroutine.h"
#include "src/lib/fxl/macros.h"
#include "src/lib/fxl/strings/string_view.h"
namespace ledger {
using PageWasEvicted = bool;
// The policy for evicting pages.
class PageEvictionPolicy {
PageEvictionPolicy() {}
virtual ~PageEvictionPolicy() {}
// Given an iterator over all pages currently stored on disk, chooses and
// tries to evict those that match the implementing policy. The status
// returned through the |callback| will be |IO_ERROR| in case of failure
// during trying to evict a page; |OK| otherwise. It is not an error if no
// page was evited.
virtual void SelectAndEvict(
std::unique_ptr<storage::Iterator<const PageInfo>> pages,
fit::function<void(storage::Status)> callback) = 0;
// The condition to be checked before evicting a page.
enum PageEvictionCondition {
// Indicates the page should be deleted if possible.
// Indicates the page should be deleted only if it is empty and offline.
// The delegate used for the |PageEvictionPolicy|. Provides the methods
// necessary to evict pages.
class PageEvictionDelegate {
PageEvictionDelegate() {}
virtual ~PageEvictionDelegate() {}
// Checks whether the given page can be evicted based on the given
// |condition| and if it can, evicts it. Note that evicting a page with
// |IF_EMPTY| has no observable effect for the user, i.e. doesn't break the
// offline case. |IF_POSSIBLE| on the other hand means that a completely
// synced page might be evicted, and thus become unavailable to the user, if
// offline. Returns |IO_ERROR| through the callback in case of failure while
// retrieving information on the page, or when trying to evict it; |OK|
// otherwise. The boolean in the callback indicates whether the page was
// evicted.
virtual void TryEvictPage(
fxl::StringView ledger_name, storage::PageIdView page_id,
PageEvictionCondition condition,
fit::function<void(storage::Status, PageWasEvicted)> callback) = 0;
// Creates and returns a new Least-Recently-Used policy, which evicts the least
// recently used page among those that can be evicted. The given delegate should
// outlive the returned object.
std::unique_ptr<PageEvictionPolicy> NewLeastRecentyUsedPolicy(
coroutine::CoroutineService* corroutine_service,
PageEvictionDelegate* delegate);
} // namespace ledger