content/browser/histogram_synchronizer.h

   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 CONTENT_BROWSER_HISTOGRAM_SYNCHRONIZER_H_
   6 #define CONTENT_BROWSER_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/singleton.h"
  14 #include "base/synchronization/lock.h"
  15 #include "base/time.h"
  16 #include "content/browser/histogram_subscriber.h"
  17
  18 class MessageLoop;
  19
  20 namespace content {
  21
  22 // This class maintains state that is used to upload histogram data from the
  23 // various child processes, into the browser process. Such transactions are
  24 // usually instigated by the browser. In general, a child process will respond
  25 // by gathering snapshots of all internal histograms, calculating what has
  26 // changed since its last upload, and transmitting a pickled collection of
  27 // deltas.
  28 //
  29 // There are actually two modes of update request.  One is synchronous (and
  30 // blocks the UI thread, waiting to populate an about:histograms tab) and the
  31 // other is asynchronous, and used by the metrics services in preparation for a
  32 // log upload.
  33 //
  34 // To assure that all the processes have responded, a counter is maintained to
  35 // indicate the number of pending (not yet responsive) processes. To avoid
  36 // confusion about a response (i.e., is the process responding to a current
  37 // request for an update, or to an old request for an update) we tag each group
  38 // of requests with a sequence number. When an update arrives we can ignore it
  39 // (relative to the counter) if it does not relate to a current outstanding
  40 // sequence number.
  41 //
  42 // There is one final mode of use, where a renderer spontaneously decides to
  43 // transmit a collection of histogram data.  This is designed for use when the
  44 // renderer is terminating.  Unfortunately, renders may be terminated without
  45 // warning, and the best we can do is periodically acquire data from a tab, such
  46 // as when a page load has completed.  In this mode, the renderer uses a
  47 // reserved sequence number, different from any sequence number that might be
  48 // specified by a browser request.  Since this sequence number can't match an
  49 // outstanding sequence number, the pickled data is accepted into the browser,
  50 // but there is no impact on the counters.
  51
  52 class HistogramSynchronizer : public HistogramSubscriber {
  53  public:
  54   enum ProcessHistogramRequester {
  55     UNKNOWN,
  56     ASYNC_HISTOGRAMS,
  57   };
  58
  59   // Return pointer to the singleton instance for the current process, or NULL
  60   // if none.
  61   static HistogramSynchronizer* GetInstance();
  62
  63   // Contact all processes, and get them to upload to the browser any/all
  64   // changes to histograms. This method is called from about:histograms.
  65   static void FetchHistograms();
  66
  67   // Contact all child processes, and get them to upload to the browser any/all
  68   // changes to histograms.  When all changes have been acquired, or when the
  69   // wait time expires (whichever is sooner), post the callback to the
  70   // specified message loop. Note the callback is posted exactly once.
  71   static void FetchHistogramsAsynchronously(MessageLoop* callback_thread,
  72                                             const base::Closure& callback,
  73                                             base::TimeDelta wait_time);
  74
  75  private:
  76   friend struct DefaultSingletonTraits<HistogramSynchronizer>;
  77
  78   class RequestContext;
  79
  80   HistogramSynchronizer();
  81   virtual ~HistogramSynchronizer();
  82
  83   // Establish a new sequence number, and use it to notify all processes
  84   // (renderers, plugins, GPU, etc) of the need to supply, to the browser,
  85   // any/all changes to their histograms. |wait_time| specifies the amount of
  86   // time to wait before cancelling the requests for non-responsive processes.
  87   void RegisterAndNotifyAllProcesses(ProcessHistogramRequester requester,
  88                                      base::TimeDelta wait_time);
  89
  90   // -------------------------------------------------------
  91   // HistogramSubscriber methods for browser child processes
  92   // -------------------------------------------------------
  93
  94   // Update the number of pending processes for the given |sequence_number|.
  95   // This is called on UI thread.
  96   virtual void OnPendingProcesses(int sequence_number,
  97                                   int pending_processes,
  98                                   bool end) OVERRIDE;
  99
 100   // Send histogram_data back to caller and also record that we are waiting
 101   // for one less histogram data from child process for the given sequence
 102   // number. This method is accessible on UI thread.
 103   virtual void OnHistogramDataCollected(
 104       int sequence_number,
 105       const std::vector<std::string>& pickled_histograms) OVERRIDE;
 106
 107   // Set the callback_thread_ and callback_ members. If these members already
 108   // had values, then as a side effect, post the old callback_ to the old
 109   // callaback_thread_.  This side effect should not generally happen, but is in
 110   // place to assure correctness (that any tasks that were set, are eventually
 111   // called, and never merely discarded).
 112   void SetCallbackTaskAndThread(MessageLoop* callback_thread,
 113                                 const base::Closure& callback);
 114
 115   void ForceHistogramSynchronizationDoneCallback(int sequence_number);
 116
 117   // Internal helper function, to post task, and record callback stats.
 118   void InternalPostTask(MessageLoop* thread, const base::Closure& callback);
 119
 120   // Gets a new sequence number to be sent to processes from browser process.
 121   int GetNextAvailableSequenceNumber(ProcessHistogramRequester requester);
 122
 123   // This lock_ protects access to all members.
 124   base::Lock lock_;
 125
 126   // When a request is made to asynchronously update the histograms, we store
 127   // the task and thread we use to post a completion notification in
 128   // callback_ and callback_thread_.
 129   base::Closure callback_;
 130   MessageLoop* callback_thread_;
 131
 132   // We don't track the actual processes that are contacted for an update, only
 133   // the count of the number of processes, and we can sometimes time-out and
 134   // give up on a "slow to respond" process.  We use a sequence_number to be
 135   // sure a response from a process is associated with the current round of
 136   // requests (and not merely a VERY belated prior response).
 137   // All sequence numbers used are non-negative.
 138   // last_used_sequence_number_ is the most recently used number (used to avoid
 139   // reuse for a long time).
 140   int last_used_sequence_number_;
 141
 142   // The sequence number used by the most recent asynchronous update request to
 143   // contact all processes.
 144   int async_sequence_number_;
 145
 146   DISALLOW_COPY_AND_ASSIGN(HistogramSynchronizer);
 147 };
 148
 149 }  // namespace content
 150
 151 #endif  // CONTENT_BROWSER_HISTOGRAM_SYNCHRONIZER_H_