Computation Server
WARNING auKsys/5 has been released as stable, but this documentation has not been fully updated with changes since auKsys/4. In case of questions or mistakes, you can use the support project.
The computation server is a ROS node that can be used to run computations dyamically, and in particular for data stored in a kDB
database.
computation_server node
computation_server
is the main node for running computation. After starting, it offers the following services:
check_status
(ros_pralin_interfaces/srv/CheckStatus
) it is used to check the state of a computation.pause_processing
(ros_pralin_interfaces/srv/ControlProcessing
) it is used to pause a computation.resume_processing
(ros_pralin_interfaces/srv/ControlProcessing
) it is used to resume a computation, after it has been paused.start_processing
(ros_pralin_interfaces/srv/StartProcessing
) it is used to start a new computation.stop_processing
(ros_pralin_interfaces/srv/ControlProcessing
) it is used to stop a computation.
Note that pause_processing
and stop_processing
can only interrupt a computation between two algorithms call. So if a computation is running for a long time in an algorithm, it won’t be stopped.
check_status
, pause_processing
, resume_processing
and stop_processing
takes as an argument the UUID of the computation, the UUID was either given as an argument during start_processing
, or returned in the response.
start_processing
The start_processing
service use the following arguments:
definition
(string
): a YAML definition of the processing.uuid
(string
): uuid to identify the processing (optional, if not given, a UUID will be generated and returned).name_space
(string
): namespace to use for the topics created by the inputs/outputs. If not given, the topics are created in a namespace generated from the UUID.parameters
(string
): a YAML string defining the parameters used by the computation.repeat
(bool
): if true, the computation repeat on inputs, if false, it will ends once it has completed once.inputs_triggers
(string[]
): if empty, any input will trigger a computation, if set, only the specified inputs willinputs_mappings
(Mapping[]
): remap input topicsoutputs_mappings
(Mapping[]
): remap output topics
If the composition defined in definition
has inputs or outputs, the computation_server
will attempt to create topics for those inputs and outputs.
This require for the type of the input to be supported, otherwise, it will trigger an error.
The topic are created using the name_space
, or if no namespace is specified, using the uuid
.
Usually, in ROS, topics can be remapped when the node is started, but this is not possible with the computation server. This can be solved using the inputs_mappings
and output_mappings
. Mapping
has the following fields:
connector_name
(string
): name of the input/output, as defined in thedefinition
.topic_name
(string
): name of the topic to re-map to. If the name starts with a/
, it will be an absolute topic, otherwise it will be relative to the namespace of the server. `
run_computation
run_computation
is a program that can be used to start a new computation from the command line.
It has the following usage:
run_computation [options] pralin_compose.yaml
Where pralin_compose.yaml
is a filename with a composition definition. Alternatively, the composition can be specified in the terminal when using the --stdin
option.
The list of options are:
--help
shows the help message.--stdin
read the composition definition from the terminal, instead of a file.--repeat
repeat the calculation until it is terminated by a service call.--not-waiting
by default, the script wait until the calculation is finished, used this option if you want the script to terminate as soon as the calculation is started.--namespace ns
define the namespace used by the topics created by the computation, it default to the UUID of the calculation--parameters params
a YAML string with the parameters used by the computation.
Example of use of this program can be found in the ROS Computation Server tutorial.
Related Tutorials
- Introduction to pralin/compose and how to execute composition from the command line or an API.
- ROS Computation Server: examples of how to use the the computation server