1 // Copyright 2018 The Chromium Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_METRICS_PERSISTENT_HISTOGRAM_STORAGE_H_ 6 #define BASE_METRICS_PERSISTENT_HISTOGRAM_STORAGE_H_ 7 8 #include <string_view> 9 10 #include "base/base_export.h" 11 #include "base/files/file_path.h" 12 13 namespace base { 14 15 // This class creates a fixed sized persistent memory to allow histograms to be 16 // stored in it. When a PersistentHistogramStorage is destructed, histograms 17 // recorded during its lifetime are persisted in the directory 18 // |storage_base_dir_|/|allocator_name| (see the ctor for allocator_name). 19 // Histograms are not persisted if the storage directory does not exist on 20 // destruction. PersistentHistogramStorage should be instantiated as early as 21 // possible in the process lifetime and should never be instantiated again. 22 // Persisted histograms will eventually be reported by Chrome. 23 class BASE_EXPORT PersistentHistogramStorage { 24 public: 25 enum class StorageDirManagement { kCreate, kUseExisting }; 26 27 // Creates a process-wide storage location for histograms that will be written 28 // to a file within a directory provided by |set_storage_base_dir()| on 29 // destruction. 30 // The |allocator_name| is used both as an internal name for the allocator, 31 // well as the leaf directory name for the file to which the histograms are 32 // persisted. The string must be ASCII. 33 // |storage_dir_management| specifies if this instance reuses an existing 34 // storage directory, or is responsible for creating one. 35 PersistentHistogramStorage(std::string_view allocator_name, 36 StorageDirManagement storage_dir_management); 37 38 PersistentHistogramStorage(const PersistentHistogramStorage&) = delete; 39 PersistentHistogramStorage& operator=(const PersistentHistogramStorage&) = 40 delete; 41 42 ~PersistentHistogramStorage(); 43 44 // The storage directory isn't always known during initial construction so 45 // it's set separately. The last one wins if there are multiple calls to this 46 // method. set_storage_base_dir(const FilePath & storage_base_dir)47 void set_storage_base_dir(const FilePath& storage_base_dir) { 48 storage_base_dir_ = storage_base_dir; 49 } 50 51 // Disables histogram storage. Disable()52 void Disable() { disabled_ = true; } 53 54 private: 55 // Metrics files are written into directory 56 // |storage_base_dir_|/|allocator_name| (see the ctor for allocator_name). 57 FilePath storage_base_dir_; 58 59 // The setting of the storage directory management. 60 const StorageDirManagement storage_dir_management_; 61 62 // A flag indicating if histogram storage is disabled. It starts with false, 63 // but can be set to true by the caller who decides to throw away its 64 // histogram data. 65 bool disabled_ = false; 66 }; 67 68 } // namespace base 69 70 #endif // BASE_METRICS_PERSISTENT_HISTOGRAM_STORAGE_H_ 71