测试中的线程处理技巧

TEST(MyRegister, Read) {
  async::Loop loop{&kAsyncLoopConfigAttachToCurrentThread};
  // For illustration purposes, this is the thread-unsafe type being tested.
  MyRegister reg{loop.dispatcher()};
  // Use the object on the current thread.
  reg.SetValue(123);
  // Run any async work scheduled by the object, also on the current thread.
  ASSERT_OK(loop.RunUntilIdle());
  // Read from the object on the current thread.
  EXPECT_EQ(obj.GetValue(), 123);
}

TEST(MyRegister, Read) {
  // Creates a foreground driver dispatcher.
  fdf_testing::DriverRuntime driver_runtime;
  // For illustration purposes, this is the thread-unsafe type being tested.
  MyRegister reg{dispatcher.dispatcher()};
  // Use the object on the current thread.
  reg.SetValue(123);
  // Run any async work scheduled by the object, also on the current thread.
  driver_runtime.RunUntilIdle();
  // Read from the object on the current thread.
  EXPECT_EQ(obj.GetValue(), 123);
  ASSERT_OK(dispatcher.Stop());
}

// Let's say this function blocks and then returns some value we need.
int GetValueInABlockingWay();

TEST(MyRegister, Read) {
  // Configure the loop to register itself as the dispatcher for the
  // loop thread, such that the |MyRegister| constructor may use
  // `async_get_default_dispatcher()` to obtain the loop dispatcher.
  async::Loop loop{&kAsyncLoopConfigNoAttachToCurrentThread};
  loop.StartThread();

  // Construct the |MyRegister| on the loop thread.
  async_patterns::TestDispatcherBound<MyRegister> reg{
      loop.dispatcher(), std::in_place};

  // Schedule a |SetValue| call on the loop thread and wait for it.
  reg.SyncCall(&MyRegister::SetValue, 123);

  // Call the blocking function on the main thread.
  // This will not deadlock, because we have started a loop thread
  // earlier to process messages for the |MyRegister| object.
  int value = GetValueInABlockingWay();
  EXPECT_EQ(value, 123);

  // |GetValue| returns a value; |SyncCall| will proxy that back.
  EXPECT_EQ(reg.SyncCall(&MyRegister::GetValue), 123);
}

// Here is the bare skeleton of a driver object that makes a synchronous call.
class BlockingIO {
 public:
  BlockingIO(): dispatcher_(fdf_dispatcher_get_current_dispatcher()) {}

  // Let's say this function blocks to update the value stored in a
  // |FakeRegister|.
  void SetValueInABlockingWay(int value);

  /* Other details omitted */
};

TEST(BlockingIO, Read) {
  // Creates a foreground driver dispatcher.
  fdf_testing::DriverRuntime driver_runtime;

  // Create a background dispatcher for the |FakeRegister|.
  // This way it is safe to call into it synchronously from the |BlockingIO|.
  fdf::UnownedSynchronizedDispatcher register_dispatcher =
      driver_runtime.StartBackgroundDispatcher();

  // Construct the |FakeRegister| on the background dispatcher.
  // The |FakeRegister| constructor may use
  // `fdf_dispatcher_get_current_dispatcher()` to obtain the dispatcher.
  async_patterns::TestDispatcherBound<FakeRegister> reg{
      register_dispatcher.async_dispatcher(), std::in_place};

  // Construct the |BlockingIO| on the foreground driver dispatcher.
  BlockingIO io;

  // Call the blocking function. The |register_dispatcher| will respond to it in the
  // background.
  io.SetValueInABlockingWay(123);

  // Check the value from the fake.
  // |GetValue| returns an |int|; |SyncCall| will proxy that back.
  // |PerformBlockingWork| will ensure the foreground dispatcher is running while
  // the blocking work runs in a new temporary background thread.
  EXPECT_EQ(driver_runtime.PerformBlockingWork([&reg]() {
    return reg.SyncCall(&FakeRegister::GetValue);
  }), 123);
}