chromium/chrome/browser/history/history_test_utils.cc

// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <memory>
#include <utility>

#include "base/run_loop.h"
#include "base/task/cancelable_task_tracker.h"
#include "chrome/browser/history/history_service_factory.h"
#include "components/history/core/browser/history_db_task.h"
#include "components/history/core/browser/history_service.h"
#include "content/public/test/test_utils.h"

namespace {

// Note: WaitableEvent is not used for synchronization between the main thread
// and history backend thread because the history subsystem posts tasks back
// to the main thread. Had we tried to Signal an event in such a task
// and Wait for it on the main thread, the task would not run at all because
// the main thread would be blocked on the Wait call, resulting in a deadlock.

// A task to be scheduled on the history backend thread.
// Notifies the main thread after all history backend thread tasks have run.
class WaitForHistoryTask : public history::HistoryDBTask { … };

}  // namespace

void WaitForHistoryBackendToRun(Profile* profile) { … }