Example of context manager to ease working with CARLA Simulator in synchronous mode.

CarlaSyncMode.py

# Example of context manager to ease working with CARLA Simulator in synchronous
# mode. Creates an object that synchronizes the data of every sensor.

# ==============================================================================
# -- Usage example -------------------------------------------------------------
# ==============================================================================


import carla


def usage_example():
    client = carla.Client('localhost', 2000)

    world = client.get_world()

    sensors = []

    try:
        sensors.append(world.spawn_actor(
            world.get_blueprint_library().find('sensor.camera.rgb'),
            carla.Transform()))
        sensors.append(world.spawn_actor(
            world.get_blueprint_library().find('sensor.camera.depth'),
            carla.Transform()))
        sensors.append(world.spawn_actor(
            world.get_blueprint_library().find('sensor.camera.semantic_segmentation'),
            carla.Transform()))
        sensors.append(world.spawn_actor(
            world.get_blueprint_library().find('sensor.lidar.ray_cast'),
            carla.Transform()))

        # Create a context in which the synchronous mode is enabled.
        with CarlaSyncMode(world, *sensors) as sync_mode:
            while True:

                # The returned object has a "tick" method that advances the
                # simulation one frame and returns the data of all the sensors
                # generated during that frame.
                data = sync_mode.tick(timeout=1.0)

                # The first element is a "carla.WorldSnapshot" containing the
                # transforms, velocities, etc. of every object in the world at
                # that precise frame.
                snapshot = data[0]

                # The rest of elements in the list are the different data
                # objects generated by the sensors; images, point-cloud, etc.
                for n, item in enumerate(data[1:]):
                    item.save_to_disk('_out/%01d_%08d' % (n, sync_mode.frame))

    finally:
        for sensor in sensors:
            sensor.destroy()

            
# ==============================================================================
# -- CarlaSyncMode Context Manager ---------------------------------------------
# ==============================================================================


import carla


try:
    import queue
except ImportError:
    import Queue as queue


class CarlaSyncMode(object):
    def __init__(self, world, *sensors):
        self.world = world
        self.sensors = sensors
        self.frame = None
        self._queues = []

    def __enter__(self):
        settings = self.world.get_settings()
        settings.synchronous_mode = True
        self._sync(self.world.apply_settings(settings))

        def make_queue(register_event):
            q = queue.Queue()
            register_event(q.put)
            self._queues.append(q)

        make_queue(self.world.on_tick)
        for sensor in self.sensors:
            make_queue(sensor.listen)
        return self

    def tick(self, timeout):
        self._sync(self.world.tick())
        data = [self._retrieve_data(q, timeout) for q in self._queues]
        assert all(x.frame == self.frame for x in data)
        return data

    def __exit__(self, type, value, traceback):
        settings = self.world.get_settings()
        settings.synchronous_mode = False
        self.world.apply_settings(settings)

    def _sync(self, frame):
        while frame > self.world.get_snapshot().timestamp.frame:
            pass
        assert frame == self.world.get_snapshot().timestamp.frame
        self.frame = frame

    def _retrieve_data(self, queue, timeout):
        while True:
            data = queue.get(timeout=timeout)
            if data.frame == self.frame:
                return data