Histograms - Support histograms for Plugins, GPU

content/browser/histogram_synchronizer_impl.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_
+#ifndef CONTENT_BROWSER_HISTOGRAM_SYNCHRONIZER_IMPL_H_
+#define CONTENT_BROWSER_HISTOGRAM_SYNCHRONIZER_IMPL_H_
 #pragma once
 
 #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"
+#include "content/browser/histogram_subscriber.h"
+#include "content/public/browser/histogram_synchronizer.h"
 
 class MessageLoop;
 
+namespace content {
+
 // 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.
+// various renderer and child processes, into the browser process. Such

[jam, 2012/06/07 03:34:33]

nit: renderer is a child process. also below

[ramant (doing other things), 2012/06/07 23:39:25]

Done.

+// transactions are usually instigated by the browser. In general, a
+// renderer/child 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.
+// To assure that all the processes have responded, a counter is maintained to
+// indicate the number of pending (not yet responsive) processes. To avoid
+// confusion about a response (i.e., is the process 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> {
+class CONTENT_EXPORT HistogramSynchronizerImpl

[jam, 2012/06/07 03:34:33]

are you sure you need to export this?

[ramant (doing other things), 2012/06/07 23:39:25]

Done.

+    : public content::HistogramSynchronizer,
+      public content::HistogramSubscriber {
  public:
-
-  enum RendererHistogramRequester {
+  enum ProcessHistogramRequester {
+    UNKNOWN,
     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();
+  HistogramSynchronizerImpl();
+
+ private:
+  friend class HistogramSynchronizer;

[jam, 2012/06/07 03:34:33]

why?

[ramant (doing other things), 2012/06/07 23:39:25]

Added public static method FetchHistogramsAsynchronously and deleted the friend
class.

+
+  class RequestContext;
+
+  virtual ~HistogramSynchronizerImpl();
 
   // Return pointer to the singleton instance, which is allocated and
   // deallocated on the main UI thread (during system startup and teardown).
-  static HistogramSynchronizer* CurrentSynchronizer();
+  static HistogramSynchronizerImpl* 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);
+  // Establish a new sequence number, and use it to notify all processes
+  // (renderers, plugins, GPU, etc) of the need to supply, to the browser,
+  // any/all changes to their histograms. It also posts a task

[jam, 2012/06/07 03:34:33]

in this class, the comments are too verbose. you don't need to describe what the
implementation does internally. just enough for the caller to know when to use
this

[ramant (doing other things), 2012/06/07 23:39:25]

Done.

+  // (RequestContext::Unregister) that would be called after waiting
+  // for |wait_time| (this task acts as a watchdog, to cancel the requests for
+  // non-responsive processes). |requester| argument indicates whether this will
+  // set async_sequence_number_ or not and that sequence number is registered in
+  // |outstanding_requests_| map.
+  void RegisterAndNotifyAllProcesses(ProcessHistogramRequester requester,
+                                     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);
+  // -------------------------------------------------------
+  // HistogramSubscriber methods for browser child processes
+  // -------------------------------------------------------
 
-  // 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);
+  // Update the number of pending processes for the given |sequence_number|.
+  // This is called on UI thread.
+  virtual void OnPendingProcesses(int sequence_number,
+                                  int pending_processes,
+                                  bool end) OVERRIDE;
 
- private:
-  friend class base::RefCountedThreadSafe<HistogramSynchronizer>;
+  // Send histogram_data back to caller by calling

[jam, 2012/06/07 03:34:33]

usually people don't document what the implementation of an overridden function
does in its header

[ramant (doing other things), 2012/06/07 23:39:25]

Done.

+  // DecrementPendingProcessesAndSendData which records that we are waiting
+  // for one less histogram data from renderer or browser child process for the
+  // given sequence number. This method is accessible on UI thread.
+  virtual void OnHistogramDataCollected(
+      int sequence_number,
+      const std::vector<std::string>& histogram_data) OVERRIDE;
 
-  ~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);
+  // It finds the RequestContext for the given |sequence_number| and notifies
+  // the RequestContext's |callback_| about the |value|. This is called
+  // whenever we receive histogram data from processes. It also records that we
+  // are waiting for one less histogram data from a process for the given
+  // sequence number. If we have received a response from all renderers and
+  // browser child processes, then it calls RequestContext's DeleteIfAllDone to
+  // delete the entry for sequence_number. This method is accessible on UI
+  // thread.
+  void DecrementPendingProcessesAndSendData(
+      int sequence_number,
+      const std::vector<std::string>& histogram_data);
 
   // 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);
 
-  // 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);
+  // Gets a new sequence number to be sent to processes from browser process.
+  int GetNextAvailableSequenceNumber(ProcessHistogramRequester requster);
 
   // 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
+  // We don't track the actual processes that are contacted for an update, only
+  // the count of the number of processes, and we can sometimes time-out and
+  // give up on a "slow to respond" process.  We use a sequence_number to be
+  // sure a response from a process 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.
+  // contact all processes.
   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);
+  DISALLOW_COPY_AND_ASSIGN(HistogramSynchronizerImpl);
 };
 
-#endif  // CHROME_BROWSER_METRICS_HISTOGRAM_SYNCHRONIZER_H_
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_HISTOGRAM_SYNCHRONIZER_IMPL_H_