// 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_