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// Copyright 2018 The Chromium 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 "base/base_export.h"
#include "base/files/file_path.h"
#include "base/macros.h"
#include "base/strings/string_piece.h"
namespace base {
// This class creates a fixed sized persistent memory to allow histograms to be
// stored in it. When a PersistentHistogramStorage is destructed, histograms
// recorded during its lifetime are persisted in the directory
// |storage_base_dir_|/|allocator_name| (see the ctor for allocator_name).
// Histograms are not persisted if the storage directory does not exist on
// destruction. PersistentHistogramStorage should be instantiated as early as
// possible in the process lifetime and should never be instantiated again.
// Persisted histograms will eventually be reported by Chrome.
class BASE_EXPORT PersistentHistogramStorage {
enum class StorageDirManagement { kCreate, kUseExisting };
// Creates a process-wide storage location for histograms that will be written
// to a file within a directory provided by |set_storage_base_dir()| on
// destruction.
// The |allocator_name| is used both as an internal name for the allocator,
// well as the leaf directory name for the file to which the histograms are
// persisted. The string must be ASCII.
// |storage_dir_management| specifies if this instance reuses an existing
// storage directory, or is responsible for creating one.
PersistentHistogramStorage(StringPiece allocator_name,
StorageDirManagement storage_dir_management);
// The storage directory isn't always known during initial construction so
// it's set separately. The last one wins if there are multiple calls to this
// method.
void set_storage_base_dir(const FilePath& storage_base_dir) {
storage_base_dir_ = storage_base_dir;
// Disables histogram storage.
void Disable() { disabled_ = true; }
// Metrics files are written into directory
// |storage_base_dir_|/|allocator_name| (see the ctor for allocator_name).
FilePath storage_base_dir_;
// The setting of the storage directory management.
const StorageDirManagement storage_dir_management_;
// A flag indicating if histogram storage is disabled. It starts with false,
// but can be set to true by the caller who decides to throw away its
// histogram data.
bool disabled_ = false;
} // namespace base