[Offline pages] Introduces TaskQueue to serialize tasks that asynchronously access SQLStore

components/offline_pages/core/task_queue_unittest.cc

+// Copyright 2016 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.
+
+#include "components/offline_pages/core/task_queue.h"
+
+#include <memory>
+
+#include "base/bind.h"
+#include "base/test/test_simple_task_runner.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace offline_pages {
+
+namespace {
+
+enum class TaskState { NOT_STARTED, STEP_1, STEP_2, COMPLETED };
+
+// Sample resource consumed by the task during execution. In this set of tests
+// used to provide the capability to continue the task.
+class ConsumedResource {
+ public:
+  void Step(const base::Closure& step_callback) { next_step_ = step_callback; }
+  void CompleteStep() {
+    base::Closure temp_ = next_step_;
+    next_step_.Reset();
+    temp_.Run();
+  }
+  bool HasNextStep() const { return !next_step_.is_null(); }
+
+ private:
+  base::Closure next_step_;
+};
+
+// Sample test task. This should not be used as a example of task implementation
+// with respect to callback safety. Otherwise it captures the idea of splitting
+// the work into multiple steps separated by potentially asynchronous calls
+// spanning multiple threads.
+class TestTask : public TaskQueue::Task {
+ public:
+  explicit TestTask(ConsumedResource* resource)
+      : resource_(resource),
+        state_(TaskState::NOT_STARTED),
+        leave_early_(false) {}
+  TestTask(ConsumedResource* resource, bool leave_early)
+      : resource_(resource),
+        state_(TaskState::NOT_STARTED),
+        leave_early_(leave_early) {}
+  ~TestTask() override {}
+
+  // Run is Step 1 in our case.
+  void Run() override {
+    state_ = TaskState::STEP_1;
+    resource_->Step(base::Bind(&TestTask::Step2, base::Unretained(this)));
+  }
+
+  void Step2() {
+    if (leave_early_) {
+      LastStep();
+      return;
+    }
+    state_ = TaskState::STEP_2;
+    resource_->Step(base::Bind(&TestTask::LastStep, base::Unretained(this)));
+  }
+
+  // This is step 3, but we conclude here.
+  void LastStep() {
+    state_ = TaskState::COMPLETED;
+    Complete();
+  }
+
+  TaskState state() const { return state_; }
+
+ private:
+  ConsumedResource* resource_;
+  TaskState state_;
+  bool leave_early_;
+};
+
+}  // namespace
+
+class OfflineTaskQueueTest : public testing::Test {
+ public:
+  OfflineTaskQueueTest();
+
+  void TaskCompleted(TaskQueue::Task* task);
+  void PumpLoop();
+
+  TaskQueue::Task* completed_task() const { return completed_task_; }
+
+ private:
+  TaskQueue::Task* completed_task_;
+  scoped_refptr<base::TestSimpleTaskRunner> task_runner_;
+  base::ThreadTaskRunnerHandle task_runner_handle_;
+};
+
+OfflineTaskQueueTest::OfflineTaskQueueTest()
+    : completed_task_(nullptr),
+      task_runner_(new base::TestSimpleTaskRunner),
+      task_runner_handle_(task_runner_) {}
+
+void OfflineTaskQueueTest::PumpLoop() {
+  task_runner_->RunUntilIdle();
+}
+
+void OfflineTaskQueueTest::TaskCompleted(TaskQueue::Task* task) {
+  completed_task_ = task;
+}
+
+TEST_F(OfflineTaskQueueTest, RunTaskStepByStep) {
+  ConsumedResource resource;
+  TestTask task(&resource);
+  task.SetCompletionCallback(
+      base::ThreadTaskRunnerHandle::Get(),
+      base::Bind(&OfflineTaskQueueTest::TaskCompleted, base::Unretained(this)));
+
+  EXPECT_EQ(TaskState::NOT_STARTED, task.state());
+  task.Run();
+  EXPECT_EQ(TaskState::STEP_1, task.state());
+  EXPECT_TRUE(resource.HasNextStep());
+  resource.CompleteStep();
+  EXPECT_EQ(TaskState::STEP_2, task.state());
+  EXPECT_TRUE(resource.HasNextStep());
+  resource.CompleteStep();
+  EXPECT_EQ(TaskState::COMPLETED, task.state());
+  PumpLoop();
+  EXPECT_EQ(completed_task(), &task);
+}
+
+TEST_F(OfflineTaskQueueTest, AddAndRunSingleTask) {
+  ConsumedResource resource;
+  std::unique_ptr<TestTask> task(new TestTask(&resource));
+  TestTask* task_ptr = task.get();
+  TaskQueue queue;
+  EXPECT_EQ(TaskState::NOT_STARTED, task_ptr->state());
+  queue.AddTask(std::move(task));
+  EXPECT_TRUE(queue.HasTasks());
+  EXPECT_TRUE(queue.CurrentlyRunning());
+  EXPECT_EQ(TaskState::STEP_1, task_ptr->state());
+  EXPECT_TRUE(resource.HasNextStep());
+  resource.CompleteStep();
+
+  EXPECT_EQ(TaskState::STEP_2, task_ptr->state());
+  EXPECT_TRUE(resource.HasNextStep());
+  resource.CompleteStep();
+
+  EXPECT_EQ(TaskState::COMPLETED, task_ptr->state());
+  EXPECT_FALSE(resource.HasNextStep());
+  PumpLoop();  // Deletes task, task_ptr is invalid after that.
+
+  EXPECT_FALSE(queue.CurrentlyRunning());
+  EXPECT_FALSE(queue.HasTasks());
+}
+
+TEST_F(OfflineTaskQueueTest, AddAndRunMultipleTasks) {
+  ConsumedResource resource;
+  std::unique_ptr<TestTask> task_1(new TestTask(&resource));
+  TestTask* task_1_ptr = task_1.get();
+  std::unique_ptr<TestTask> task_2(new TestTask(&resource));
+  TestTask* task_2_ptr = task_2.get();
+
+  TaskQueue queue;
+  EXPECT_EQ(TaskState::NOT_STARTED, task_1_ptr->state());
+  EXPECT_EQ(TaskState::NOT_STARTED, task_2_ptr->state());
+  queue.AddTask(std::move(task_1));
+  queue.AddTask(std::move(task_2));
+  EXPECT_TRUE(queue.HasTasks());
+  EXPECT_TRUE(queue.CurrentlyRunning());
+  EXPECT_EQ(TaskState::STEP_1, task_1_ptr->state());
+  EXPECT_EQ(TaskState::NOT_STARTED, task_2_ptr->state());
+  resource.CompleteStep();
+
+  EXPECT_EQ(TaskState::STEP_2, task_1_ptr->state());
+  EXPECT_EQ(TaskState::NOT_STARTED, task_2_ptr->state());
+  resource.CompleteStep();
+
+  EXPECT_EQ(TaskState::COMPLETED, task_1_ptr->state());
+  EXPECT_EQ(TaskState::NOT_STARTED, task_2_ptr->state());
+  PumpLoop();  // Deletes task_1, task_1_ptr is invalid after that.
+  EXPECT_EQ(TaskState::STEP_1, task_2_ptr->state());
+}
+
+TEST_F(OfflineTaskQueueTest, LeaveEearly) {
+  ConsumedResource resource;
+  std::unique_ptr<TestTask> task(new TestTask(&resource, true));
+  TestTask* task_ptr = task.get();
+  TaskQueue queue;
+  EXPECT_EQ(TaskState::NOT_STARTED, task_ptr->state());
+  queue.AddTask(std::move(task));
+  EXPECT_TRUE(queue.HasTasks());
+  EXPECT_TRUE(queue.CurrentlyRunning());
+  EXPECT_EQ(TaskState::STEP_1, task_ptr->state());
+  EXPECT_TRUE(resource.HasNextStep());
+  resource.CompleteStep();
+
+  EXPECT_EQ(TaskState::COMPLETED, task_ptr->state());
+  EXPECT_FALSE(resource.HasNextStep());
+  PumpLoop();  // Deletes task, task_ptr is invalid after that.
+
+  EXPECT_FALSE(queue.CurrentlyRunning());
+  EXPECT_FALSE(queue.HasTasks());
+}
+
+}  // namespace offline_pages