history_url_provider.h | Explore in Territory

// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_OMNIBOX_BROWSER_HISTORY_URL_PROVIDER_H_
#define COMPONENTS_OMNIBOX_BROWSER_HISTORY_URL_PROVIDER_H_

#include <stddef.h>

#include <memory>
#include <string>
#include <vector>

#include "base/compiler_specific.h"
#include "base/gtest_prod_util.h"
#include "base/memory/raw_ptr.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/atomic_flag.h"
#include "base/threading/thread_checker.h"
#include "components/omnibox/browser/autocomplete_input.h"
#include "components/omnibox/browser/history_match.h"
#include "components/omnibox/browser/history_provider.h"
#include "components/omnibox/browser/omnibox_field_trial.h"
#include "components/search_engines/template_url.h"

class AutocompleteProviderListener;
class SearchTermsData;

namespace base {
class SequencedTaskRunner;
}

namespace history {
class HistoryBackend;
class URLDatabase;
}  // namespace history

// How history autocomplete works
// ==============================
//
// Read down this diagram for temporal ordering.
//
//   Main thread                History thread
//   -----------                --------------
//   AutocompleteController::Start
//     -> HistoryURLProvider::Start
//       -> VerbatimMatchForInput
//       [params_ allocated]
//       -> DoAutocomplete (for inline autocomplete)
//         -> URLDatabase::AutocompleteForPrefix (on in-memory DB)
//       -> HistoryService::ScheduleAutocomplete
//       (return to controller) ----
//                                 /
//                            HistoryBackend::ScheduleAutocomplete
//                              -> HistoryURLProvider::ExecuteWithDB
//                                -> DoAutocomplete
//                                  -> URLDatabase::AutocompleteForPrefix
//                              /
//   HistoryService::QueryComplete
//     [params_ destroyed]
//     -> AutocompleteProviderListener::OnProviderUpdate
//
// The autocomplete controller calls us, and must be called back, on the main
// thread.  When called, we run two autocomplete passes.  The first pass runs
// synchronously on the main thread and queries the in-memory URL database.
// This pass promotes matches for inline autocomplete if applicable.  We do
// this synchronously so that users get consistent behavior when they type
// quickly and hit enter, no matter how loaded the main history database is.
// Doing this synchronously also prevents inline autocomplete from being
// "flickery" in the AutocompleteEdit.  Because the in-memory DB does not have
// redirect data, results other than the top match might change between the
// two passes, so we can't just decide to use this pass' matches as the final
// results.
//
// The second autocomplete pass uses the full history database, which must be
// queried on the history thread.  Start() asks the history service schedule to
// callback on the history thread with a pointer to the main database.  When we
// are done doing queries, we schedule a task on the main thread that notifies
// the AutocompleteController that we're done.
//
// The communication between these threads is done using a
// HistoryURLProviderParams object.  This is allocated in the main thread, and
// normally deleted in QueryComplete().  So that both autocomplete passes can
// use the same code, we also use this to hold results during the first
// autocomplete pass.
//
// While the second pass is running, the AutocompleteController may cancel the
// request.  This can happen frequently when the user is typing quickly.  In
// this case, the main thread sets params_->cancel, which the background thread
// checks periodically.  If it finds the flag set, it stops what it's doing
// immediately and calls back to the main thread.  (We don't delete the params
// on the history thread, because we should only do that when we can safely
// NULL out params_, and that must be done on the main thread.)

// Used to communicate autocomplete parameters between threads via the history
// service.
struct HistoryURLProviderParams { … };

// This class is an autocomplete provider and is also a pseudo-internal
// component of the history system.  See comments above.
class HistoryURLProvider : public HistoryProvider { … };

#endif  // COMPONENTS_OMNIBOX_BROWSER_HISTORY_URL_PROVIDER_H_
chromium/components/omnibox/browser/history_url_provider.h
