1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 // 5 // A StatsTable is a table of statistics. It can be used across multiple 6 // processes and threads, maintaining cheap statistics counters without 7 // locking. 8 // 9 // The goal is to make it very cheap and easy for developers to add 10 // counters to code, without having to build one-off utilities or mechanisms 11 // to track the counters, and also to allow a single "view" to display 12 // the contents of all counters. 13 // 14 // To achieve this, StatsTable creates a shared memory segment to store 15 // the data for the counters. Upon creation, it has a specific size 16 // which governs the maximum number of counters and concurrent 17 // threads/processes which can use it. 18 // 19 20 #ifndef BASE_METRICS_STATS_TABLE_H_ 21 #define BASE_METRICS_STATS_TABLE_H_ 22 #pragma once 23 24 #include <string> 25 26 #include "base/base_api.h" 27 #include "base/basictypes.h" 28 #include "base/hash_tables.h" 29 #include "base/synchronization/lock.h" 30 #include "base/threading/thread_local_storage.h" 31 32 namespace base { 33 34 class BASE_API StatsTable { 35 public: 36 // Create a new StatsTable. 37 // If a StatsTable already exists with the specified name, this StatsTable 38 // will use the same shared memory segment as the original. Otherwise, 39 // a new StatsTable is created and all counters are zeroed. 40 // 41 // name is the name of the StatsTable to use. 42 // 43 // max_threads is the maximum number of threads the table will support. 44 // If the StatsTable already exists, this number is ignored. 45 // 46 // max_counters is the maximum number of counters the table will support. 47 // If the StatsTable already exists, this number is ignored. 48 StatsTable(const std::string& name, int max_threads, int max_counters); 49 50 // Destroys the StatsTable. When the last StatsTable is destroyed 51 // (across all processes), the StatsTable is removed from disk. 52 ~StatsTable(); 53 54 // For convenience, we create a static table. This is generally 55 // used automatically by the counters. 56 static StatsTable* current() { return global_table_; } 57 58 // Set the global table for use in this process. 59 static void set_current(StatsTable* value) { global_table_ = value; } 60 61 // Get the slot id for the calling thread. Returns 0 if no 62 // slot is assigned. 63 int GetSlot() const; 64 65 // All threads that contribute data to the table must register with the 66 // table first. This function will set thread local storage for the 67 // thread containing the location in the table where this thread will 68 // write its counter data. 69 // 70 // name is just a debugging tag to label the thread, and it does not 71 // need to be unique. It will be truncated to kMaxThreadNameLength-1 72 // characters. 73 // 74 // On success, returns the slot id for this thread. On failure, 75 // returns 0. 76 int RegisterThread(const std::string& name); 77 78 // Returns the number of threads currently registered. This is really not 79 // useful except for diagnostics and debugging. 80 int CountThreadsRegistered() const; 81 82 // Find a counter in the StatsTable. 83 // 84 // Returns an id for the counter which can be used to call GetLocation(). 85 // If the counter does not exist, attempts to create a row for the new 86 // counter. If there is no space in the table for the new counter, 87 // returns 0. 88 int FindCounter(const std::string& name); 89 90 // TODO(mbelshe): implement RemoveCounter. 91 92 // Gets the location of a particular value in the table based on 93 // the counter id and slot id. 94 int* GetLocation(int counter_id, int slot_id) const; 95 96 // Gets the counter name at a particular row. If the row is empty, 97 // returns NULL. 98 const char* GetRowName(int index) const; 99 100 // Gets the sum of the values for a particular row. 101 int GetRowValue(int index) const; 102 103 // Gets the sum of the values for a particular row for a given pid. 104 int GetRowValue(int index, int pid) const; 105 106 // Gets the sum of the values for a particular counter. If the counter 107 // does not exist, creates the counter. 108 int GetCounterValue(const std::string& name); 109 110 // Gets the sum of the values for a particular counter for a given pid. 111 // If the counter does not exist, creates the counter. 112 int GetCounterValue(const std::string& name, int pid); 113 114 // The maxinum number of counters/rows in the table. 115 int GetMaxCounters() const; 116 117 // The maxinum number of threads/columns in the table. 118 int GetMaxThreads() const; 119 120 // The maximum length (in characters) of a Thread's name including 121 // null terminator, as stored in the shared memory. 122 static const int kMaxThreadNameLength = 32; 123 124 // The maximum length (in characters) of a Counter's name including 125 // null terminator, as stored in the shared memory. 126 static const int kMaxCounterNameLength = 64; 127 128 // Convenience function to lookup a counter location for a 129 // counter by name for the calling thread. Will register 130 // the thread if it is not already registered. 131 static int* FindLocation(const char *name); 132 133 private: 134 class Private; 135 struct TLSData; 136 typedef hash_map<std::string, int> CountersMap; 137 138 // Returns the space occupied by a thread in the table. Generally used 139 // if a thread terminates but the process continues. This function 140 // does not zero out the thread's counters. 141 // Cannot be used inside a posix tls destructor. 142 void UnregisterThread(); 143 144 // This variant expects the tls data to be passed in, so it is safe to 145 // call from inside a posix tls destructor (see doc for pthread_key_create). 146 void UnregisterThread(TLSData* tls_data); 147 148 // The SlotReturnFunction is called at thread exit for each thread 149 // which used the StatsTable. 150 static void SlotReturnFunction(void* data); 151 152 // Locates a free slot in the table. Returns a number > 0 on success, 153 // or 0 on failure. The caller must hold the shared_memory lock when 154 // calling this function. 155 int FindEmptyThread() const; 156 157 // Locates a counter in the table or finds an empty row. Returns a 158 // number > 0 on success, or 0 on failure. The caller must hold the 159 // shared_memory_lock when calling this function. 160 int FindCounterOrEmptyRow(const std::string& name) const; 161 162 // Internal function to add a counter to the StatsTable. Assumes that 163 // the counter does not already exist in the table. 164 // 165 // name is a unique identifier for this counter, and will be truncated 166 // to kMaxCounterNameLength-1 characters. 167 // 168 // On success, returns the counter_id for the newly added counter. 169 // On failure, returns 0. 170 int AddCounter(const std::string& name); 171 172 // Get the TLS data for the calling thread. Returns NULL if none is 173 // initialized. 174 TLSData* GetTLSData() const; 175 176 Private* impl_; 177 178 // The counters_lock_ protects the counters_ hash table. 179 base::Lock counters_lock_; 180 181 // The counters_ hash map is an in-memory hash of the counters. 182 // It is used for quick lookup of counters, but is cannot be used 183 // as a substitute for what is in the shared memory. Even though 184 // we don't have a counter in our hash table, another process may 185 // have created it. 186 CountersMap counters_; 187 ThreadLocalStorage::Slot tls_index_; 188 189 static StatsTable* global_table_; 190 191 DISALLOW_COPY_AND_ASSIGN(StatsTable); 192 }; 193 194 } // namespace base 195 196 #endif // BASE_METRICS_STATS_TABLE_H_ 197
