LCM
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The Lua API wraps the LCM C API, and is meant to mirror its functionality and organization. The bulk of the Lua API is represented by the LCM userdata, which basically wraps lcm_t and related functions.
The LCM userdata manages an internal lcm_t and any number of subscriptions.
Initializer
Methods
Parameters
provider
Optional. The LCM provider.Return Values
Description
This is the userdata initializer; it creates a new userdata.
Example Code
local lcm = require('lcm') local lc = lcm.lcm.new() local lc2 = lcm.lcm.new('udpm://239.255.76.67:7667?ttl=1')
Parameters
channel
The channel to publish to. message
The encoded message to send.Return Values
Description
This method publishes a message to a channel. If the message cannot be published, an error is raised.
Example Code
local lcm = require('lcm') local msg_t = require('msg_t') -- or any other message type local lc = lcm.lcm.new() local msg = msg_t:new() local encoded_msg = msg:encode() lc:publish('somechannel', encoded_msg)
Parameters
channel
The channel to subscribe to. handler
The callback.Return Values
Description
This method creates a subscription to a channel. There may be multiple subscriptions per channel. Creating a subscription involves registering a callback, which is invoked once per received message on the specified channel. The callback is invoked during calls to handle or timedhandle.
Notice that this function does not return an actual subscription, but a reference to one. This function returns an integer which is used to index an internal table of subscriptions. The lifetime of the internal subscription is not dependent on the reference, so subscriptions cannot be garbage collected. Subscriptions can only be removed by being unsubscribed.
Example Code
local lcm = require('lcm') local msg_t = require('msg_t') -- or any other message type local lc = lcm.lcm.new() local function handler(channel, encoded_msg) local msg = msg_t.decode(encoded_msg) -- ... end local sub = lc:subscribe('somechannel', handler)
Parameters
sub
The subscription refernce to unsubscribe.Return Values
Description
The method removes a subscription created by subscribe. Also note that all subscriptions are automatically unsubscribed when the LCM userdata is garbage collected.
Example Code
local lcm = require('lcm') local msg_t = require('msg_t') -- or any other message type local lc = lcm.lcm.new() local function handler(channel, encoded_msg) local msg = msg_t.decode(encoded_msg) -- ... end local sub = lc:subscribe('somechannel', handler) --- ... lc:unsubscribe(sub)
Parameters
Return Values
Description
Waits for an incomming message, and dispatches handler callbacks as necessary. This method will block indefinitely until a message is recieved. When a message is received, all of the handler callbacks for the message's channel are invoked, in the same order they were subscribed.
Example Code
local lcm = require('lcm') local lc = lcm.lcm.new() lc:handle()
Parameters
time
The time to block, in milliseconds.Return Values
true
if a message was received and handled, false
otherwise.Description
This method is like the normal handle except it only blocks for a specified amount of time.
Example Code
local lcm = require('lcm') local lc = lcm.lcm.new() local ok = lc:handle_timeout(500) if not ok then print('timed out!') end
This function is deprecated! Please use handle_timeout instead!
Parameters
time
The time to block, in seconds.Return Values
true
if a message was received and handled, false
otherwise.Description
This method is like the normal handle except it only blocks for a specified amount of time.
Example Code
local lcm = require('lcm') local lc = lcm.lcm.new() local ok = lc:timedhandle(0.5) if not ok then print('timed out!') end