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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef COMPONENTS_PERSISTENT_CACHE_PERSISTENT_CACHE_H_
#define COMPONENTS_PERSISTENT_CACHE_PERSISTENT_CACHE_H_
#include <memory>
#include <string_view>
#include <utility>
#include "base/component_export.h"
#include "base/containers/span.h"
#include "base/files/file.h"
#include "components/persistent_cache/backend_params.h"
#include "components/persistent_cache/entry_metadata.h"
namespace persistent_cache {
class Entry;
class Backend;
// Use PersistentCache to store and retrieve key-value pairs across processes or
// threads.
//
// Example:
// // Create a persistent cache backend.
// BackendParams backend_params = AcquireParams();
// auto PersistentCache persistent_cache =
// PersistentCache::Open(backend_params);
// if(!persistent_cache){
// // Handle error.
// }
//
// // Add a key-value pair.
// persistent_cache->Insert("foo", base::byte_span_from_cstring("1"));
//
// // Retrieve a value. The presence of the key and its value are guaranteed
// // during the lifetime of `entry`.
// {
// auto entry = persistent_cache->Find("foo");
//
// // Warning: The value may have changed since insertion (because the
// // cache is multi-thread/multi-process), been evicted by the backend, or
// // the initial insertion may have failed.
// if (entry) {
// UseEntry(entry);
// }
// }
//
// // Inserting again overwrites anything in there if present.
// persistent_cache->Insert("foo", base::byte_span_from_cstring("2"));
//
// Use PersistentCache to store and retrieve key-value pairs across processes or
// threads.
class COMPONENT_EXPORT(PERSISTENT_CACHE) PersistentCache {
public:
explicit PersistentCache(std::unique_ptr<Backend> backend);
~PersistentCache();
// Not copyable or moveable.
PersistentCache(const PersistentCache&) = delete;
PersistentCache(PersistentCache&&) = delete;
PersistentCache& operator=(const PersistentCache&) = delete;
PersistentCache& operator=(PersistentCache&&) = delete;
// Used to open a cache with a backend of type `impl`. Returns nullptr in
// case of failure.
static std::unique_ptr<PersistentCache> Open(BackendParams backend_params);
// Used to get a handle to entry associated with `key`. Returns `nullptr` if
// `key` is not found. Returned entry will remain valid and its contents will
// be accessible for its entire lifetime. Note: Persistent caches have to
// outlive entries they vend.
//
// Thread-safe.
std::unique_ptr<Entry> Find(std::string_view key);
// Used to add an entry containing `content` and associated with `key`.
//
// Thread-safe.
void Insert(std::string_view key,
base::span<const uint8_t> content,
EntryMetadata metadata = EntryMetadata{});
Backend* GetBackendForTesting();
private:
std::unique_ptr<Backend> backend_;
};
} // namespace persistent_cache
#endif // COMPONENTS_PERSISTENT_CACHE_PERSISTENT_CACHE_H_
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