Histograms - Support histograms for Plugins, GPU

chrome/browser/metrics/histogram_synchronizer.h

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef CHROME_BROWSER_METRICS_HISTOGRAM_SYNCHRONIZER_H_
-#define CHROME_BROWSER_METRICS_HISTOGRAM_SYNCHRONIZER_H_
-
-#include <string>
-#include <vector>
-
-#include "base/basictypes.h"
-#include "base/callback.h"
-#include "base/memory/ref_counted.h"
-#include "base/synchronization/condition_variable.h"
-#include "base/synchronization/lock.h"
-#include "base/time.h"
-
-class MessageLoop;
-
-// This class maintains state that is used to upload histogram data from the
-// various renderer processes, into the browser process.  Such transactions are
-// usually instigated by the browser.  In general, a renderer process will
-// respond by gathering snapshots of all internal histograms, calculating what
-// has changed since its last upload, and transmitting a pickled collection of
-// deltas.
-//
-// There are actually two modes of update request.  One is synchronous (and
-// blocks the UI thread, waiting to populate an about:histograms tab) and the
-// other is asynchronous, and used by the metrics services in preparation for a
-// log upload.
-//
-// To assure that all the renderers have responded, a counter is maintained (for
-// each mode) to indicate the number of pending (not yet responsive) renderers.
-// To avoid confusion about a response (i.e., is the renderer responding to a
-// current request for an update, or to an old request for an update) we tag
-// each group of requests with a sequence number.  When an update arrives we can
-// ignore it (relative to the counter) if it does not relate to a current
-// outstanding sequence number.
-//
-// There is one final mode of use, where a renderer spontaneously decides to
-// transmit a collection of histogram data.  This is designed for use when the
-// renderer is terminating.  Unfortunately, renders may be terminated without
-// warning, and the best we can do is periodically acquire data from a tab, such
-// as when a page load has completed.  In this mode, the renderer uses a
-// reserved sequence number, different from any sequence number that might be
-// specified by a browser request.  Since this sequence number can't match an
-// outstanding sequence number, the pickled data is accepted into the browser,
-// but there is no impact on the counters.
-
-class HistogramSynchronizer : public
-    base::RefCountedThreadSafe<HistogramSynchronizer> {
- public:
-
-  enum RendererHistogramRequester {
-    ASYNC_HISTOGRAMS,
-    SYNCHRONOUS_HISTOGRAMS
-  };
-
-  // Construction also sets up the global singleton instance.  This instance is
-  // used to communicate between the IO and UI thread, and is destroyed only
-  // as the main thread (browser_main) terminates, which means the IO thread has
-  // already completed, and will not need this instance any further.
-  HistogramSynchronizer();
-
-  // Return pointer to the singleton instance, which is allocated and
-  // deallocated on the main UI thread (during system startup and teardown).
-  static HistogramSynchronizer* CurrentSynchronizer();
-
-  // Contact all renderers, and get them to upload to the browser any/all
-  // changes to histograms.  Return when all changes have been acquired, or when
-  // the wait time expires (whichever is sooner). This method is called on the
-  // main UI thread from about:histograms.
-  void FetchRendererHistogramsSynchronously(base::TimeDelta wait_time);
-
-  // Contact all renderers, and get them to upload to the browser any/all
-  // changes to histograms.  When all changes have been acquired, or when the
-  // wait time expires (whichever is sooner), post the callback to the
-  // specified message loop. Note the callback is posted exactly once.
-  static void FetchRendererHistogramsAsynchronously(
-      MessageLoop* callback_thread,
-      const base::Closure& callback,
-      base::TimeDelta wait_time);
-
-  // This method is called on the IO thread. Deserializes the histograms and
-  // records that we have received histograms from a renderer process.
-  static void DeserializeHistogramList(
-      int sequence_number, const std::vector<std::string>& histograms);
-
- private:
-  friend class base::RefCountedThreadSafe<HistogramSynchronizer>;
-
-  ~HistogramSynchronizer();
-
-  // Establish a new sequence_number_, and use it to notify all the renderers of
-  // the need to supply, to the browser, any changes in their histograms.
-  // The argument indicates whether this will set async_sequence_number_ or
-  // synchronous_sequence_number_.
-  // Return the sequence number that was used.
-  int NotifyAllRenderers(RendererHistogramRequester requester);
-
-  // Records that we are waiting for one less histogram from a renderer for the
-  // given sequence number. If we have received a response from all renderers,
-  // either signal the waiting process or call the callback function.
-  void DecrementPendingRenderers(int sequence_number);
-
-  // Set the callback_thread_ and callback_ members. If these members already
-  // had values, then as a side effect, post the old callback_ to the old
-  // callaback_thread_.  This side effect should not generally happen, but is in
-  // place to assure correctness (that any tasks that were set, are eventually
-  // called, and never merely discarded).
-  void SetCallbackTaskAndThread(MessageLoop* callback_thread,
-                                const base::Closure& callback);
-
-  void ForceHistogramSynchronizationDoneCallback(int sequence_number);
-
-  // Gets a new sequence number to be sent to renderers from browser process and
-  // set the number of pending responses for the given type to renderer_count.
-  int GetNextAvailableSequenceNumber(RendererHistogramRequester requster,
-                                     int renderer_count);
-
-  // Internal helper function, to post task, and record callback stats.
-  void InternalPostTask(MessageLoop* thread,
-                        const base::Closure& callback,
-                        int unresponsive_renderers,
-                        const base::TimeTicks& started);
-
-  // This lock_ protects access to all members.
-  base::Lock lock_;
-
-  // This condition variable is used to block caller of the synchronous request
-  // to update histograms, and to signal that thread when updates are completed.
-  base::ConditionVariable received_all_renderer_histograms_;
-
-  // When a request is made to asynchronously update the histograms, we store
-  // the task and thread we use to post a completion notification in
-  // callback_ and callback_thread_.
-  base::Closure callback_;
-  MessageLoop* callback_thread_;
-
-  // We don't track the actual renderers that are contacted for an update, only
-  // the count of the number of renderers, and we can sometimes time-out and
-  // give up on a "slow to respond" renderer.  We use a sequence_number to be
-  // sure a response from a renderer is associated with the current round of
-  // requests (and not merely a VERY belated prior response).
-  // All sequence numbers used are non-negative.
-  // last_used_sequence_number_ is the most recently used number (used to avoid
-  // reuse for a long time).
-  int last_used_sequence_number_;
-
-  // The sequence number used by the most recent asynchronous update request to
-  // contact all renderers.
-  int async_sequence_number_;
-
-  // The number of renderers that have not yet responded to requests (as part of
-  // an asynchronous update).
-  int async_renderers_pending_;
-
-  // The time when we were told to start the fetch histograms asynchronously
-  // from renderers.
-  base::TimeTicks async_callback_start_time_;
-
-  // The sequence number used by the most recent synchronous update request to
-  // contact all renderers.
-  int synchronous_sequence_number_;
-
-  // The number of renderers that have not yet responded to requests (as part of
-  // a synchronous update).
-  int synchronous_renderers_pending_;
-
-  // This singleton instance should be started during the single threaded
-  // portion of main(). It initializes globals to provide support for all future
-  // calls. This object is created on the UI thread, and it is destroyed after
-  // all the other threads have gone away. As a result, it is ok to call it
-  // from the UI thread (for UMA uploads), or for about:histograms.
-  static HistogramSynchronizer* histogram_synchronizer_;
-
-  DISALLOW_COPY_AND_ASSIGN(HistogramSynchronizer);
-};
-
-#endif  // CHROME_BROWSER_METRICS_HISTOGRAM_SYNCHRONIZER_H_