| // 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/callback.h" |
| #include "base/macros.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 base::DefaultSingletonTraits<HistogramSynchronizer>; |
| |
| class RequestContext; |
| |
| HistogramSynchronizer(); |
| ~HistogramSynchronizer() override; |
| |
| // 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. |
| 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. |
| 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_ |