subscribers.py

Go to the documentation of this file.

# Software License Agreement (BSD License)
#
# Copyright (c) 2012, Willow Garage, Inc.
# Copyright (c) 2013, PAL Robotics SL
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
#  * Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
#  * Redistributions in binary form must reproduce the above
#    copyright notice, this list of conditions and the following
#    disclaimer in the documentation and/or other materials provided
#    with the distribution.
#  * Neither the name of Willow Garage, Inc. nor the names of its
#    contributors may be used to endorse or promote products derived
#    from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
 
from threading import Lock
from rospy import Subscriber, logerr
from rostopic import get_topic_type
from rosbridge_library.internal import ros_loader, message_conversion
from rosbridge_library.internal.topics import TopicNotEstablishedException
from rosbridge_library.internal.topics import TypeConflictException
from rosbridge_library.internal.outgoing_message import OutgoingMessage
from rospy.msg import AnyMsg
 
""" Manages and interfaces with ROS Subscriber objects.  A single subscriber
is shared between multiple clients
"""
 
 
class MultiSubscriber():
    """ Handles multiple clients for a single subscriber.
 
    Converts msgs to JSON before handing them to callbacks.  Due to subscriber
    callbacks being called in separate threads, must lock whenever modifying
    or accessing the subscribed clients. """
 
    def __init__(self, topic, msg_type=None):
        """ Register a subscriber on the specified topic.
 
        Keyword arguments:
        topic    -- the name of the topic to register the subscriber on
        msg_type -- (optional) the type to register the subscriber as.  If not
        provided, an attempt will be made to infer the topic type
 
        Throws:
        TopicNotEstablishedException -- if no msg_type was specified by the
        caller and the topic is not yet established, so a topic type cannot
        be inferred
        TypeConflictException        -- if the msg_type was specified by the
        caller and the topic is established, and the established type is
        different to the user-specified msg_type
 
        """
        # First check to see if the topic is already established
        topic_type = get_topic_type(topic)[0]
 
        # If it's not established and no type was specified, exception
        if msg_type is None and topic_type is None:
            raise TopicNotEstablishedException(topic)
 
        # Use the established topic type if none was specified
        if msg_type is None:
            msg_type = topic_type
 
        if msg_type == "__AnyMsg":
            msg_class = AnyMsg
        else:
            # Load the message class, propagating any exceptions from bad msg types
            msg_class = ros_loader.get_message_class(msg_type)
 
            # Make sure the specified msg type and established msg type are same
            if topic_type is not None and topic_type != msg_class._type:
                raise TypeConflictException(topic, topic_type, msg_class._type)
 
        # Create the subscriber and associated member variables
        self.subscriptions = {}
        self.lock = Lock()
        self.topic = topic
        self.msg_class = msg_class
        self.subscriber = Subscriber(topic, msg_class, self.callback)
 
    def unregister(self):
        self.subscriber.unregister()
        with self.lock:
            self.subscriptions.clear()
 
    def verify_type(self, msg_type):
        """ Verify that the subscriber subscribes to messages of this type.
 
        Keyword arguments:
        msg_type -- the type to check this subscriber against
 
        Throws:
        Exception -- if ros_loader cannot load the specified msg type
        TypeConflictException -- if the msg_type is different than the type of
        this publisher
 
        """
        if msg_type == "__AnyMsg":
            return
        if not ros_loader.get_message_class(msg_type) is self.msg_class:
            raise TypeConflictException(self.topic,
                                        self.msg_class._type, msg_type)
 
    def subscribe(self, client_id, callback):
        """ Subscribe the specified client to this subscriber.
 
        Keyword arguments:
        client_id -- the ID of the client subscribing
        callback  -- this client's callback, that will be called for incoming
        messages
 
        """
        with self.lock:
            self.subscriptions[client_id] = callback
            # If the topic is latched, add_callback will immediately invoke
            # the given callback.
            self.subscriber.impl.add_callback(self.callback, [callback])
            self.subscriber.impl.remove_callback(self.callback, [callback])
 
    def unsubscribe(self, client_id):
        """ Unsubscribe the specified client from this subscriber
 
        Keyword arguments:
        client_id -- the ID of the client to unsubscribe
 
        """
        with self.lock:
            del self.subscriptions[client_id]
 
    def has_subscribers(self):
        """ Return true if there are subscribers """
        with self.lock:
            return len(self.subscriptions) != 0
 
    def callback(self, msg, callbacks=None):
        """ Callback for incoming messages on the rospy.Subscriber
 
        Passes the message to registered subscriber callbacks.
 
        Keyword Arguments:
        msg - the ROS message coming from the subscriber
        callbacks - subscriber callbacks to invoke
 
        """
        outgoing = OutgoingMessage(msg)
 
        # Get the callbacks to call
        if not callbacks:
            with self.lock:
                callbacks = list(self.subscriptions.values())
 
        # Pass the JSON to each of the callbacks
        for callback in callbacks:
            try:
                callback(outgoing)
            except Exception as exc:
                # Do nothing if one particular callback fails except log it
                logerr("Exception calling subscribe callback: %s", exc)
 
 
class SubscriberManager():
    """
    Keeps track of client subscriptions
    """
 
    def __init__(self):
        self._lock = Lock()
        self._subscribers = {}
 
    def subscribe(self, client_id, topic, callback, msg_type=None):
        """ Subscribe to a topic
 
        Keyword arguments:
        client_id -- the ID of the client making this subscribe request
        topic     -- the name of the topic to subscribe to
        callback  -- the callback to call for incoming messages on the topic
        msg_type  -- (optional) the type of the topic
 
        """
        with self._lock:
            if not topic in self._subscribers:
                self._subscribers[topic] = MultiSubscriber(topic, msg_type)
 
            if msg_type is not None:
                self._subscribers[topic].verify_type(msg_type)
 
            self._subscribers[topic].subscribe(client_id, callback)
 
    def unsubscribe(self, client_id, topic):
        """ Unsubscribe from a topic
 
        Keyword arguments:
        client_id -- the ID of the client to unsubscribe
        topic     -- the topic to unsubscribe from
 
        """
        with self._lock:
            if topic in self._subscribers:
                self._subscribers[topic].unsubscribe(client_id)
 
                if not self._subscribers[topic].has_subscribers():
                    self._subscribers[topic].unregister()
                    del self._subscribers[topic]
 
 
manager = SubscriberManager()