# roboflex.transport.zmq
Roboflex support for the ZMQ transport.
any node -> ZMQPublisher ==THEINTERNET==> ZMQSubscriber -> any node
See https://zeromq.org/ for details.
Using ZMQ, nodes can connect to other nodes, running in different threads, different processes, or different computers, with a publisher-subscriber pattern. roboflex.transport.zmq supports:
"inproc" transport -> between threads within same process
"ipc" transport -> between processes on same computer
"tcp" transport -> between processes on different computers
## System Dependencies
None! We build libzmq from source...
## pip install
pip install roboflex.transport.zmq
## Import (python)
import roboflex.transport.zmq as rtz
## Build (for c++ projects):
mkdir build && cd build
cmake ..
make
make install
## Run Examples (see [examples](examples))
go to roboflex_transport_zmq/examples
... create and activate some sort of virtual environment
where you installed roboflex.transport.zmq...
python pub_sub_0_py.py
## Nodes:
There are three: `ZMQContext`, `ZMQPublisher`, `ZMQSubscriber`.
To use the ZMQ transport nodes, first you must create a ZMQContext object. This mirrors the design of ZMQ itself.
# all parameters optional
zmq_context = ZMQContext(
num_io_threads = 1,
)
First, know this. "bind addresses" in this world can be three different things. All are strings, but can create different types of queues. These all implement one-to-many publish-subscribe pattern (in fact, it's actually many-to-many).
1. thread-to-thread only queues; "inproc://somename"; the fastest.
2. process-to-process (or thread-to-thread) queues; "ipc://somename"; sort of fast.
3. computer-to-computer (can work anywhere) queues (uses TCP): "tcp://*:5647"; the slowest, but works across the planet.
Then, create a ZMQPublisher:
zmq_pub = ZMQPublisher(
# the ZMQContext object you created
zmq_context,
# what socket to bind to, or what transport to publish on
bind_address = <bind address>,
# or
bind_addresses = [<bind address>],
# optional
# name of the
name = "ZMQPublisher",
# same as 'high-water mark' in zeromq parlance
max_queued_msgs = 1000,
)
#... when a ZMQPublisher receives a message from some upstream node, #it will wire-serialize it, and publish on its transport.
#You can get the bind_addresses:
ba = zmq_pub.bind_addresses
# you can get the high-water mark
hm = zmq_pub.max_queued_msgs
# You can publish a message 'by hand' - same as calling 'receive' on the node.
zmq_pub.publish(some_message)
Then, create one or more ZMQSubscribers, to listen to what you are publishing. ZMQSubscribes are the equivalent of 'sensors' in that the are root nodes, must be started, and start a thread.
zmq_sub = ZMQSubscriber(
# the ZMQContext object you created
zmq_context,
# what socket to bind to, or what transport to subscribe on
connect_address = <bind address>,
# or
connect_addresses = [<bind address>],
# optional
# name of the
name = "ZMQPublisher",
# same as 'high-water mark' in zeromq parlance
max_queued_msgs = 1000,
# how often to yield control on the thread
# You'll probably never change this.
timeout_milliseconds = 10,
)
# you get get values
zmq_sub.connect_addresses
zmq_sub.connect_address
zmq_sub.max_queued_msgs
zmq_sub.timeout_milliseconds
# you MUST start it!
zmq_sub.start()
# you may pull a message 'by hand':
msg_or_none = zmq_sub.pull(
10, # timeout_milliseconds - how long to wait for a message
)
# you may 'produce' messages 'by hand' - this will wait x milliseconds
# for one message, and if it has received one, signals it downstream
zmq_sub.produce(
10, # timeout_milliseconds
)
Raw data
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