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// Copyright 2021 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_METRICS_STRUCTURED_LIB_PERSISTENT_PROTO_H_
#define COMPONENTS_METRICS_STRUCTURED_LIB_PERSISTENT_PROTO_H_
#include <concepts>
#include <memory>
#include <type_traits>
#include "components/metrics/structured/lib/persistent_proto_internal.h"
#include "third_party/protobuf/src/google/protobuf/message_lite.h"
namespace metrics::structured {
// PersistentProto wraps a proto class and persists it to disk. Usage summary.
// - Init is asynchronous, usage before |on_read| is called will crash.
// - pproto->Method() will call Method on the underlying proto.
// - Call QueueWrite() to write to disk.
//
// Reading. The backing file is read asynchronously from disk once at
// initialization, and the |on_read| callback is run once this is done. Until
// |on_read| is called, has_value is false and get() will always return nullptr.
// If no proto file exists on disk, or it is invalid, a blank proto is
// constructed and immediately written to disk.
//
// Writing. Writes must be triggered manually. QueueWrite() delays writing to
// disk for |write_delay| time, in order to batch successive writes.
// The |on_write| callback is run each time a write has completed. QueueWrite()
// should not be called until OnReadComplete() is finished, which can be
// checked with the callback |on_read_|. Calling QueueWrite() before
// OnReadComplete() has finished will result in a crash.
//
// The |on_write| callback is run each time a write has completed.
//
// This class is NOT thread-safe and access to the proto should be on the same
// sequence |this| is constructed.
template <class T>
requires(std::derived_from<T, google::protobuf::MessageLite>)
class PersistentProto : public internal::PersistentProtoInternal {
public:
using internal::PersistentProtoInternal::PersistentProtoInternal;
PersistentProto(const base::FilePath& path,
base::TimeDelta write_delay,
PersistentProtoInternal::ReadCallback on_read,
PersistentProtoInternal::WriteCallback on_write)
: internal::PersistentProtoInternal(path,
write_delay,
std::move(on_read),
std::move(on_write)),
handle_(std::make_unique<T>()) {}
~PersistentProto() override { DeallocProto(); }
T* get() { return static_cast<T*>(internal::PersistentProtoInternal::get()); }
const T* get() const {
return static_cast<T*>(internal::PersistentProtoInternal::get());
}
T* operator->() { return get(); }
const T* operator->() const { return get(); }
T& operator*() { return *get(); }
const T& operator*() const { return *get(); }
private:
google::protobuf::MessageLite* GetProto() override { return handle_.get(); }
std::unique_ptr<T> handle_;
};
} // namespace metrics::structured
#endif // COMPONENTS_METRICS_STRUCTURED_LIB_PERSISTENT_PROTO_H_
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