Script server design

Wiki > The Backend System > Nicos > Script server design

What it should do

• Accept multiple clients
• Serve up a list of available commands for the specified instrument over some protocol. The command should contain command parameters and a description, for example:
  • Name: set_ei
  • Parameters: incident energy (double)
  • Description: Positions the choppers to allow the specified incident energy through
• The commands are instrument specific scripts written by the instrument scientists and/or controls team, and are stored on the server
• New commands can be added relatively quickly without requiring changes to the client
• Accept and queue up jobs from clients and add them to the job queue
• Provide feedback on the status of the job queue
• Provide feedback on the status of the current job (% done, current line etc.)
• Iterate through the job queue
• Execute the jobs, one at a time from the queue
• Allow the job queue to be edited (e.g. reordered, jobs skipped or repeated)
• Allow the current job to be paused or aborted
• When a job is paused the next action is to resume it or abort it. It is not possible to run a different job then return to the paused job
• If the job is paused and the user manually changes the beamline then that change is keep when the job is resumed
• If a job is aborted it can be run again, but it will start from the beginning; however, it can be edited before being re-run
• Allow individual jobs to be edited (excluding the current job?)
• Provide a description of what existing jobs consist of (to allow editing)
• Provide an estimate of how long a job will take
• Provide the elapsed time for the current job
• Run a black-box script as a job (see submitted scripts section below)
• Provide script validation, e.g. allow a dry run of a script or job
• Provide robust error handling and reporting

Submitted scripts

Different types of script:

• Script server aware – created by a script generator
  • Loops unwound so each iteration is used to produce a job
  • Each job has tags for providing feedback, such as progress information, to the clients
• Script server aware – written by hand
  • Includes tags for the script server to provide extra functionality for the script server; such as “pause points” and progress information
• Black-box scripts – written by hand
  • Contains no information for the script server
  • Script server runs it as a single job but cannot pause it or report progress
  • Can be aborted

Architectural design

Decisions already made:

• Scripts, commands and jobs will be written and run in CPython

A simple diagram of the design:

Commands:

• The instrument specific commands are loaded from a certain area on the NDX
• The command sources contain documentation describing the command and the parameters
• The list of commands and their information are served

Jobs:

• The Job Queue contains the jobs to be run
• The jobs are Python scripts/snippets
• The Job Manager is responsible for managing the queue and the running of the job
• For each job the Manager spawns a new [#point1 (1)] Python process to run the job
• If the job is configured correctly the Job Manager can query the status of the job

This means there is no state shared between jobs – do we want this?

Security

There are two levels of security. Logging into the script server and logging into NICOS. Logging onto the script server allows you to put commands onto the queue. Both passwords and usernames should be readable by the GUI via PVs secured in the block server. In the future we can have users with different levels those that can write to the system can access a different user account to those who don't.