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1 // Copyright (c) 2012 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 #ifndef CHROME_BROWSER_METRICS_HISTOGRAM_SYNCHRONIZER_H_ | |
6 #define CHROME_BROWSER_METRICS_HISTOGRAM_SYNCHRONIZER_H_ | |
7 | |
8 #include <string> | |
9 #include <vector> | |
10 | |
11 #include "base/basictypes.h" | |
12 #include "base/callback.h" | |
13 #include "base/memory/ref_counted.h" | |
14 #include "base/synchronization/condition_variable.h" | |
15 #include "base/synchronization/lock.h" | |
16 #include "base/time.h" | |
17 | |
18 class MessageLoop; | |
19 | |
20 // This class maintains state that is used to upload histogram data from the | |
21 // various renderer processes, into the browser process. Such transactions are | |
22 // usually instigated by the browser. In general, a renderer process will | |
23 // respond by gathering snapshots of all internal histograms, calculating what | |
24 // has changed since its last upload, and transmitting a pickled collection of | |
25 // deltas. | |
26 // | |
27 // There are actually two modes of update request. One is synchronous (and | |
28 // blocks the UI thread, waiting to populate an about:histograms tab) and the | |
29 // other is asynchronous, and used by the metrics services in preparation for a | |
30 // log upload. | |
31 // | |
32 // To assure that all the renderers have responded, a counter is maintained (for | |
33 // each mode) to indicate the number of pending (not yet responsive) renderers. | |
34 // To avoid confusion about a response (i.e., is the renderer responding to a | |
35 // current request for an update, or to an old request for an update) we tag | |
36 // each group of requests with a sequence number. When an update arrives we can | |
37 // ignore it (relative to the counter) if it does not relate to a current | |
38 // outstanding sequence number. | |
39 // | |
40 // There is one final mode of use, where a renderer spontaneously decides to | |
41 // transmit a collection of histogram data. This is designed for use when the | |
42 // renderer is terminating. Unfortunately, renders may be terminated without | |
43 // warning, and the best we can do is periodically acquire data from a tab, such | |
44 // as when a page load has completed. In this mode, the renderer uses a | |
45 // reserved sequence number, different from any sequence number that might be | |
46 // specified by a browser request. Since this sequence number can't match an | |
47 // outstanding sequence number, the pickled data is accepted into the browser, | |
48 // but there is no impact on the counters. | |
49 | |
50 class HistogramSynchronizer : public | |
51 base::RefCountedThreadSafe<HistogramSynchronizer> { | |
52 public: | |
53 | |
54 enum RendererHistogramRequester { | |
55 ASYNC_HISTOGRAMS, | |
56 SYNCHRONOUS_HISTOGRAMS | |
57 }; | |
58 | |
59 // Construction also sets up the global singleton instance. This instance is | |
60 // used to communicate between the IO and UI thread, and is destroyed only | |
61 // as the main thread (browser_main) terminates, which means the IO thread has | |
62 // already completed, and will not need this instance any further. | |
63 HistogramSynchronizer(); | |
64 | |
65 // Return pointer to the singleton instance, which is allocated and | |
66 // deallocated on the main UI thread (during system startup and teardown). | |
67 static HistogramSynchronizer* CurrentSynchronizer(); | |
68 | |
69 // Contact all renderers, and get them to upload to the browser any/all | |
70 // changes to histograms. Return when all changes have been acquired, or when | |
71 // the wait time expires (whichever is sooner). This method is called on the | |
72 // main UI thread from about:histograms. | |
73 void FetchRendererHistogramsSynchronously(base::TimeDelta wait_time); | |
74 | |
75 // Contact all renderers, and get them to upload to the browser any/all | |
76 // changes to histograms. When all changes have been acquired, or when the | |
77 // wait time expires (whichever is sooner), post the callback to the | |
78 // specified message loop. Note the callback is posted exactly once. | |
79 static void FetchRendererHistogramsAsynchronously( | |
80 MessageLoop* callback_thread, | |
81 const base::Closure& callback, | |
82 base::TimeDelta wait_time); | |
83 | |
84 // This method is called on the IO thread. Deserializes the histograms and | |
85 // records that we have received histograms from a renderer process. | |
86 static void DeserializeHistogramList( | |
87 int sequence_number, const std::vector<std::string>& histograms); | |
88 | |
89 private: | |
90 friend class base::RefCountedThreadSafe<HistogramSynchronizer>; | |
91 | |
92 ~HistogramSynchronizer(); | |
93 | |
94 // Establish a new sequence_number_, and use it to notify all the renderers of | |
95 // the need to supply, to the browser, any changes in their histograms. | |
96 // The argument indicates whether this will set async_sequence_number_ or | |
97 // synchronous_sequence_number_. | |
98 // Return the sequence number that was used. | |
99 int NotifyAllRenderers(RendererHistogramRequester requester); | |
100 | |
101 // Records that we are waiting for one less histogram from a renderer for the | |
102 // given sequence number. If we have received a response from all renderers, | |
103 // either signal the waiting process or call the callback function. | |
104 void DecrementPendingRenderers(int sequence_number); | |
105 | |
106 // Set the callback_thread_ and callback_ members. If these members already | |
107 // had values, then as a side effect, post the old callback_ to the old | |
108 // callaback_thread_. This side effect should not generally happen, but is in | |
109 // place to assure correctness (that any tasks that were set, are eventually | |
110 // called, and never merely discarded). | |
111 void SetCallbackTaskAndThread(MessageLoop* callback_thread, | |
112 const base::Closure& callback); | |
113 | |
114 void ForceHistogramSynchronizationDoneCallback(int sequence_number); | |
115 | |
116 // Gets a new sequence number to be sent to renderers from browser process and | |
117 // set the number of pending responses for the given type to renderer_count. | |
118 int GetNextAvailableSequenceNumber(RendererHistogramRequester requster, | |
119 int renderer_count); | |
120 | |
121 // Internal helper function, to post task, and record callback stats. | |
122 void InternalPostTask(MessageLoop* thread, | |
123 const base::Closure& callback, | |
124 int unresponsive_renderers, | |
125 const base::TimeTicks& started); | |
126 | |
127 // This lock_ protects access to all members. | |
128 base::Lock lock_; | |
129 | |
130 // This condition variable is used to block caller of the synchronous request | |
131 // to update histograms, and to signal that thread when updates are completed. | |
132 base::ConditionVariable received_all_renderer_histograms_; | |
133 | |
134 // When a request is made to asynchronously update the histograms, we store | |
135 // the task and thread we use to post a completion notification in | |
136 // callback_ and callback_thread_. | |
137 base::Closure callback_; | |
138 MessageLoop* callback_thread_; | |
139 | |
140 // We don't track the actual renderers that are contacted for an update, only | |
141 // the count of the number of renderers, and we can sometimes time-out and | |
142 // give up on a "slow to respond" renderer. We use a sequence_number to be | |
143 // sure a response from a renderer is associated with the current round of | |
144 // requests (and not merely a VERY belated prior response). | |
145 // All sequence numbers used are non-negative. | |
146 // last_used_sequence_number_ is the most recently used number (used to avoid | |
147 // reuse for a long time). | |
148 int last_used_sequence_number_; | |
149 | |
150 // The sequence number used by the most recent asynchronous update request to | |
151 // contact all renderers. | |
152 int async_sequence_number_; | |
153 | |
154 // The number of renderers that have not yet responded to requests (as part of | |
155 // an asynchronous update). | |
156 int async_renderers_pending_; | |
157 | |
158 // The time when we were told to start the fetch histograms asynchronously | |
159 // from renderers. | |
160 base::TimeTicks async_callback_start_time_; | |
161 | |
162 // The sequence number used by the most recent synchronous update request to | |
163 // contact all renderers. | |
164 int synchronous_sequence_number_; | |
165 | |
166 // The number of renderers that have not yet responded to requests (as part of | |
167 // a synchronous update). | |
168 int synchronous_renderers_pending_; | |
169 | |
170 // This singleton instance should be started during the single threaded | |
171 // portion of main(). It initializes globals to provide support for all future | |
172 // calls. This object is created on the UI thread, and it is destroyed after | |
173 // all the other threads have gone away. As a result, it is ok to call it | |
174 // from the UI thread (for UMA uploads), or for about:histograms. | |
175 static HistogramSynchronizer* histogram_synchronizer_; | |
176 | |
177 DISALLOW_COPY_AND_ASSIGN(HistogramSynchronizer); | |
178 }; | |
179 | |
180 #endif // CHROME_BROWSER_METRICS_HISTOGRAM_SYNCHRONIZER_H_ | |
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