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1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. | 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 | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 // | 4 // |
5 // A StatsTable is a table of statistics. It can be used across multiple | 5 // A StatsTable is a table of statistics. It can be used across multiple |
6 // processes and threads, maintaining cheap statistics counters without | 6 // processes and threads, maintaining cheap statistics counters without |
7 // locking. | 7 // locking. |
8 // | 8 // |
9 // The goal is to make it very cheap and easy for developers to add | 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 | 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 | 11 // to track the counters, and also to allow a single "view" to display |
12 // the contents of all counters. | 12 // the contents of all counters. |
13 // | 13 // |
14 // To achieve this, StatsTable creates a shared memory segment to store | 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 | 15 // the data for the counters. Upon creation, it has a specific size |
16 // which governs the maximum number of counters and concurrent | 16 // which governs the maximum number of counters and concurrent |
17 // threads/processes which can use it. | 17 // threads/processes which can use it. |
18 // | 18 // |
19 | 19 |
20 #ifndef BASE_METRICS_STATS_TABLE_H_ | 20 #ifndef BASE_METRICS_STATS_TABLE_H_ |
21 #define BASE_METRICS_STATS_TABLE_H_ | 21 #define BASE_METRICS_STATS_TABLE_H_ |
22 #pragma once | 22 #pragma once |
23 | 23 |
24 #include <string> | 24 #include <string> |
25 | 25 |
26 #include "base/basictypes.h" | 26 #include "base/basictypes.h" |
27 #include "base/hash_tables.h" | 27 #include "base/hash_tables.h" |
28 #include "base/lock.h" | 28 #include "base/synchronization/lock.h" |
29 #include "base/threading/thread_local_storage.h" | 29 #include "base/threading/thread_local_storage.h" |
30 | 30 |
31 namespace base { | 31 namespace base { |
32 | 32 |
33 class StatsTable { | 33 class StatsTable { |
34 public: | 34 public: |
35 // Create a new StatsTable. | 35 // Create a new StatsTable. |
36 // If a StatsTable already exists with the specified name, this StatsTable | 36 // If a StatsTable already exists with the specified name, this StatsTable |
37 // will use the same shared memory segment as the original. Otherwise, | 37 // will use the same shared memory segment as the original. Otherwise, |
38 // a new StatsTable is created and all counters are zeroed. | 38 // a new StatsTable is created and all counters are zeroed. |
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168 // On failure, returns 0. | 168 // On failure, returns 0. |
169 int AddCounter(const std::string& name); | 169 int AddCounter(const std::string& name); |
170 | 170 |
171 // Get the TLS data for the calling thread. Returns NULL if none is | 171 // Get the TLS data for the calling thread. Returns NULL if none is |
172 // initialized. | 172 // initialized. |
173 TLSData* GetTLSData() const; | 173 TLSData* GetTLSData() const; |
174 | 174 |
175 Private* impl_; | 175 Private* impl_; |
176 | 176 |
177 // The counters_lock_ protects the counters_ hash table. | 177 // The counters_lock_ protects the counters_ hash table. |
178 Lock counters_lock_; | 178 base::Lock counters_lock_; |
179 | 179 |
180 // The counters_ hash map is an in-memory hash of the counters. | 180 // The counters_ hash map is an in-memory hash of the counters. |
181 // It is used for quick lookup of counters, but is cannot be used | 181 // It is used for quick lookup of counters, but is cannot be used |
182 // as a substitute for what is in the shared memory. Even though | 182 // as a substitute for what is in the shared memory. Even though |
183 // we don't have a counter in our hash table, another process may | 183 // we don't have a counter in our hash table, another process may |
184 // have created it. | 184 // have created it. |
185 CountersMap counters_; | 185 CountersMap counters_; |
186 ThreadLocalStorage::Slot tls_index_; | 186 ThreadLocalStorage::Slot tls_index_; |
187 | 187 |
188 static StatsTable* global_table_; | 188 static StatsTable* global_table_; |
189 | 189 |
190 DISALLOW_COPY_AND_ASSIGN(StatsTable); | 190 DISALLOW_COPY_AND_ASSIGN(StatsTable); |
191 }; | 191 }; |
192 | 192 |
193 } // namespace base | 193 } // namespace base |
194 | 194 |
195 #endif // BASE_METRICS_STATS_TABLE_H_ | 195 #endif // BASE_METRICS_STATS_TABLE_H_ |
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