Why isn't trollius making this loop run asynchronously?

Question

I am trying to write some simple loops to control objects in Pygazebo, but alas it only ever calls the method once and then the loops appears to block.

# -*- coding: utf-8 -*-
"""
Created on Thu Jul  2 12:52:50 2015

@author: skylion
"""

import trollius #NOTE: Trollius requires protobuffer from Google
from trollius import From

import pygazebo
import pygazebo.msg.joint_cmd_pb2
import time   

def apply_joint_force(world_name, robot_name, joint_name, force, duration=-1):


    @trollius.coroutine 
    def joint_force_loop():
        manager = yield From(pygazebo.connect())
        print("connected")


        publisher = yield From(
            manager.advertise('/gazebo/' + world_name + '/' + robot_name + '/joint_cmd',
                              'gazebo.msgs.JointCmd'))

        message = pygazebo.msg.joint_cmd_pb2.JointCmd()
        message.name = robot_name + '::' + joint_name #format should be: name_of_robot + '::name_of_joint'
        message.force = force


        #t_end = time.time() + duration # The time that you want the controller to stop
        while True: #time.time() < t_end or duration == -1:
            try:
                yield From(publisher.publish(message))
                yield From(trollius.sleep(1.0))
            except:
                pass
             #Nothing   
        print("Connection closed")

    wait_net_service('localhost',11345)


    loop = trollius.new_event_loop()
    loop.run_until_complete(joint_force_loop())
    raise     


def wait_net_service(server, port, timeout=None):
    """ Wait for network service to appear 
        @param timeout: in seconds, if None or 0 wait forever
        @return: True of False, if timeout is None may return only True or
                 throw unhandled network exception
    """
    import socket
    import errno

    s = socket.socket()
    if timeout:
        from time import time as now
        # time module is needed to calc timeout shared between two exceptions
        end = now() + timeout

    while True:
        try:
            if timeout:
                next_timeout = end - now()
                if next_timeout < 0:
                    return False
                else:
                    s.settimeout(next_timeout)
            s.connect((server, port))
            time.sleep(1)
        except socket.timeout, err:
            # this exception occurs only if timeout is set
            if timeout:
                return False

        except socket.error, err:
            # catch timeout exception from underlying network library
            # this one is different from socket.timeout
            if type(err.args) != tuple or (err[0] != errno.ETIMEDOUT and err[0] != errno.ECONNREFUSED):
                raise err
        else:
            s.close()
            return True

I thought @coroutines were suppose to be wrapped asynchronously? Do I just misunderstand the use this code? Or am I doing something else wrong? This is my first time with concurrency in Python btw.

Also this is how I am calling that function:

    counter = 0
    for joint_def in self.all_joint_props:
        print("each joint_def")
        apply_joint_force(world_name, robot_name, "hingejoint" + str(counter), joint_def[2])
        #print("Appliing joint force")

Any idea why it keep blocking the thread? Should I be using a different method to this? Any help would be appreciated

I think you need to change `wait_net_service('localhost',11345)` to `yield from wait_net_service('localhost',11345)` — Colonel Thirty Two, Jul 02 '15 at 19:51
I had this problem before I even added that method in though. So that is not the issue. — Skylion, Jul 02 '15 at 20:16

score 1 · Accepted Answer · edited May 23 '17 at 11:43

So, the answer is quite simple really. You have to queue up the multiple Trollius.Tasks you want to run as a list before starting the object and combine that with Trollius.wait() to achieve this. To ensure the thread is non-blocking you then use the following method

Here is my code so far:

tasks = []
for joint_name in joint_names:
    tasks.append(trollius.Task(joint_force_loop(world_name, robot_name, joint_name, force, duration))
loop = trollius.get_event_loop()
loop.run_until_complete(trollius.wait(tasks))

Why isn't trollius making this loop run asynchronously?

1 Answers1