typed_column.h | Explore in Territory

/*
 * Copyright (C) 2020 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef SRC_TRACE_PROCESSOR_DB_TYPED_COLUMN_H_
#define SRC_TRACE_PROCESSOR_DB_TYPED_COLUMN_H_

#include <cstdint>
#include <optional>
#include <type_traits>
#include <vector>

#include "perfetto/base/logging.h"
#include "perfetto/trace_processor/basic_types.h"
#include "src/trace_processor/containers/null_term_string_view.h"
#include "src/trace_processor/db/column.h"
#include "src/trace_processor/db/column/types.h"
#include "src/trace_processor/db/column_storage.h"
#include "src/trace_processor/db/typed_column_internal.h"

namespace perfetto::trace_processor {

// TypedColumn<T>
//
// Introduction:
// TypedColumn exists to allow efficient access to the data in a Column without
// having to go through dynamic type checking. There are two main reasons for
// this:
// 1. Performance: dynamic type checking is not free and so if this is used
//    in a particularily hot codepath, the typechecking can be a significant
//    overhead.
// 2. Ergonomics: having to convert back and forth from/to SqlValue causes
//    signifcant clutter in parts of the code which can already be quite hard
//    to follow (e.g. trackers like SequenceStackProfileTracker which perform
//    cross checking of various ids).
//
// Implementation:
// TypedColumn is implemented as a memberless subclass of Column. This allows
// us to static cast from a Column* to a TypedColumn<T> where we know the
// type T. The methods of TypedColumn are type-specialized methods of Column
// which allow callers to pass real types instead of using SqlValue.
//
// There are two helper classes (tc_internal::TypeHandler and
// tc_internal::Serializer) where we specialize behaviour which needs to be
// different based on T. See their class documentation and below for details
// on their purpose.
template <typename T>
class TypedColumn : public ColumnLegacy { … };

// Represents a column containing ids.
template <typename Id>
class IdColumn : public ColumnLegacy { … };

}  // namespace perfetto::trace_processor

#endif  // SRC_TRACE_PROCESSOR_DB_TYPED_COLUMN_H_
chromium/third_party/perfetto/src/trace_processor/db/typed_column.h
