Actor based architecture for world's largest telescope
- 1. Actor based architecture for world's largest telescope Saloni Vithalani and Unmesh Joshi
- 2. We work with people and organizations who have ambitious missions We are focused on helping our industry improve. We are strong believers in the power of software and technology as tools for social change. 4500 Employees 15 Countries 42 Offices
- 3. ● World's largest optical telescope ● Operational in 2027! ● Mauna Kea, Hawaii ● Five countries collaborating ○ USA ○ Canada ○ China ○ Japan ○ India https://www.tmt.org/
- 5. The Program Summary ● A program more than 20 years long and more.. ○ Started around 2007 ○ Going to be operational in 2027 as per current plans ○ Telescope will be operational for 50 years from the first light date. ● Software development is primarily happening in India. ○ ThoughtWorks working on ‘common software’ frameworks. ○ Built prototypes using Akka since 2014.
- 6. Overview of ‘Common Software’ ● A Mechanism For Service Discovery ● Telescope Configuration Management Service. ● Centralized Logging ● Event and Telemetry data capture mechanism ● A Timer API with PTP setup. ● A Framework For Telescope control system development. ○ Using Typed Actors.
- 8. TCS DevicesTCS DevicesTCS Devices WFS Probe Inst Devices Inst Devices Inst Devices Inst Devices Detector Devices 0: Observatory Hardware TCS HCD TCS HCD TCS HCD WFS HCD Instrument Rotation HCD Motion Control HCD-1 Motion Control HCD-2 Instrument Service Detector 1: Hardware Control Layer TCP Pointing Assembly IFS WFS Demand Assembly Instrument Rotation Assembly Filter Assembly Slit mask Assembly Science Detector Assembly Grating Assembly 2: Assembly Layer Observing Mode Telescope Sequencer Observing Mode OCS Sequencer Observing Mode Instrument Sequencer 3: Sequencing Layer 4: Monitoring and Control Applications
- 9. TCS Assembly Probe Arm Assembly (20, 35) (10, 25) (20, 35) (10, 10)(10, 10) Example Scenario Probe HCD Probe HCD Probe HCD multi-axis motor controller multi-axis motor controller motor controller
- 10. Key Characteristics ● Peer to Peer system ○ Components like Assemblies, HCDs ■ Discover other components ■ Send commands ■ Subscribe to other components’ events ● Asynchronous Message Passing ● Components are stateful ○ They maintain device state or subsystem state etc. Concurrency and Safety are important concerns
- 11. Actors! ● Message passing communication ● State management ○ Without synchronization hassles ○ Safety with supervision strategies ● Location transparency
- 12. Deployment and Discovery Akka Cluster with CRDTs Service Discovery Http and SSE Component Actors Machine 1 Machine 2
- 13. Anatomy of a TMT Component Supervisor Top Level Actor spawn() Handlers initialize() Worker spawn() Pub-Sub Manager Command Response Manager spawn() spawn() Worker Worker Provided by TMT Framework To be implemented by component writers publish() complete()
- 14. Supervisor ● Registers itself with Akka CRDT ● Any communication to a component goes via supervisor ○ Filter and validate commands received ● Manages lifecycle of the component ○ Helps restart the component in case of exception encountered during execution ○ Provide admin interface to restart, shutdown, change log level, etc. for a component
- 15. Role of Typed Actors in TMT ● Helps in defining communication protocols between components ● Makes the communication protocol explicit at compile time ○ Currently using mutable typed actors ○ Actor refs are stored in akka CRDT
- 16. Learnings ● Sealed messages for typed actors turned out to be quite rigid ○ Union type support in the language could help ● We used mutable behaviour because of familiarity ○ Eventually realized that immutable actors can do everything we wanted ● Type information of actor refs not preserved during serialization ○ No error is thrown when a deserialized actorRef is cast to incorrect type ○ Carrying type information with the serialized actorref could be useful
- 17. TCS Assembly Probe Arm Assembly Probe HCD (20, 35) demandState = (20, 35) currentState = (10, 10) move = (10, 25) (10, 25) Timer of 50ms Timer of 50ms (20, 35) (10, 10)(10, 10) Update next move = (10, 25) Demo
- 18. Team ThoughtWorks, Pune ● Mushtaq Ahmed ● Unmesh Joshi ● Pritam Kadam ● Dolly Gyanchandani ● Bilal Fazlani ● Saloni Vithalani ● Shubham Jaybhaye ● Chhaya Yadav ● Gunjan Shukla ● Santosh Mahale ● Puneet Patwari ● Poorva Gokhale ● Bharat Singh TMT, Pasadena ● Francisco Delgado ● Kim Gillies ● Allan Brighton ● Jason Weiss IIA, Bangalore ● Rajalakshmi Karthik ● Annapurni Subramaniam ● Girish M
Editor's Notes
- #2: Will be talking about
- #4: A program more than 20 years long. Started i guess back in 2007. Going to be live in 2027 as per current plans. 30 meters of diameter for primary mirror. Its not possible to have single mirror this big. So its made up of 500 mirror segments. Huge structure like a 5 storey building. Has hundreds of hardware and software components coordinating the telescope. Different countries and industrial partners are contributing to different parts of the work. India is software development responsible for most of common softwre development..
- #10: Lets take a scenario. You want to schedule an observation. Point the telescope to a particular part a sky. Calibrate the telescope. Take pictures. Continue for next 8 hours, continuously adjusting the telscope. Moving the telescope needs to coordinate several subsystems. Sequencer sends the command to Telescope control system assembly, calculates the next position. It communicates with a probe arm assembly, which talks to hardware control of the daemons to communicate with the motors to rotate.
- #11: State management makes concurrency an important aspect. Safety in failure scenarios is another important aspect
- #13: CRDT based service discovery
- #14: Component - Seq, Assembly, Hcd Assembly needs to discover hcd, send comands and handle response This are pretty common actions in telescope, So we have extracted the common protocol in a framework Developed by Thoghtworks India Different teams will use our framework Supervisor - actor by framework, first thing, spawns TLA TLA - initialize handlers TLA- handler template pattern Code display Action in handlers Execution sequence decided by TLA Handlers delegate to workers to execute a command Workers publish events while executing Worker mark command complete after execution
- #15: Front facing of component Exception in initialize bubble up to TLA to Supervisor Sup applies restart strategy Brings the component in clean state So, if I have to reason why sup is exposed as comp address instead of TLA, then it is because TLA’s ref gets chaned when it restarts and exposing a short lived address is not going to be a preferred way
- #16: Explain Typed actors All framework actors are typed actors