Initial import.

1 files changed, 154 insertions, 0 deletions

diff --git a/chromium/content/browser/histogram_synchronizer.h b/chromium/content/browser/histogram_synchronizer.h
new file mode 100644
index 00000000000..9ff69d5cfeb
--- /dev/null
+++ b/chromium/content/browser/histogram_synchronizer.h
@@ -0,0 +1,154 @@
+// 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 CONTENT_BROWSER_HISTOGRAM_SYNCHRONIZER_H_
+#define CONTENT_BROWSER_HISTOGRAM_SYNCHRONIZER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "base/memory/singleton.h"
+#include "base/synchronization/lock.h"
+#include "base/time/time.h"
+#include "content/browser/histogram_subscriber.h"
+
+namespace base {
+class MessageLoop;
+}
+
+namespace content {
+
+// This class maintains state that is used to upload histogram data from the
+// various child processes, into the browser process. Such transactions are
+// usually instigated by the browser. In general, a 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 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 HistogramSubscriber {
+ public:
+  enum ProcessHistogramRequester {
+    UNKNOWN,
+    ASYNC_HISTOGRAMS,
+  };
+
+  // Return pointer to the singleton instance for the current process, or NULL
+  // if none.
+  static HistogramSynchronizer* GetInstance();
+
+  // Contact all processes, and get them to upload to the browser any/all
+  // changes to histograms. This method is called from about:histograms.
+  static void FetchHistograms();
+
+  // Contact all child processes, 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 FetchHistogramsAsynchronously(base::MessageLoop* callback_thread,
+                                            const base::Closure& callback,
+                                            base::TimeDelta wait_time);
+
+ private:
+  friend struct DefaultSingletonTraits<HistogramSynchronizer>;
+
+  class RequestContext;
+
+  HistogramSynchronizer();
+  virtual ~HistogramSynchronizer();
+
+  // 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. |wait_time| specifies the amount of
+  // time to wait before cancelling the requests for non-responsive processes.
+  void RegisterAndNotifyAllProcesses(ProcessHistogramRequester requester,
+                                     base::TimeDelta wait_time);
+
+  // -------------------------------------------------------
+  // HistogramSubscriber methods for browser child processes
+  // -------------------------------------------------------
+
+  // 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;
+
+  // Send histogram_data back to caller and also record that we are waiting
+  // for one less histogram data from 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>& pickled_histograms) OVERRIDE;
+
+  // 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(base::MessageLoop* callback_thread,
+                                const base::Closure& callback);
+
+  void ForceHistogramSynchronizationDoneCallback(int sequence_number);
+
+  // Internal helper function, to post task, and record callback stats.
+  void InternalPostTask(base::MessageLoop* thread,
+                        const base::Closure& callback);
+
+  // Gets a new sequence number to be sent to processes from browser process.
+  int GetNextAvailableSequenceNumber(ProcessHistogramRequester requester);
+
+  // This lock_ protects access to all members.
+  base::Lock lock_;
+
+  // 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_;
+  base::MessageLoop* callback_thread_;
+
+  // 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 processes.
+  int async_sequence_number_;
+
+  DISALLOW_COPY_AND_ASSIGN(HistogramSynchronizer);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_HISTOGRAM_SYNCHRONIZER_H_