recodex-wiki/Submissions-flow.md

Submissions flow

It's assumed that readers understand Architecture, Terminology, Communication and Assignments Overview. This article will describe in detail execution flow of submission from the point of submission into web application to the point of evaluation of results from execution. Only hot path is considered in following description.

Web Application

First thing user has to submit his/her solution to web application. Generally web application has to store submitted files and hand over all needed information about submission to broker. More detailed description follows:

• user submits his solution to web application
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Broker

Broker gets information about new submission from web application. At this point broker has to find suitable worker for execution of this particular submission. When worker is found and is jobless, then broker send detailed submission to worker to evaluation. More detailed description follows:

• broker gets multipart "eval" message from web application with job identification, source archive URL, result URL and appropriate worker headers
• headers are parsed and worker which matches all of them is chosen as the one which will execute incoming submission
• whole execution request is saved into worker structure to waiting queue
• if chosen worker is not working right now then incoming request is forwarded directly from waiting queue to worker through multipart message
• if worker queue is not empty then nothing is done right now
  • execution of this particular request is suspended until worker complete all previous requests

Worker

Worker gets request from broker to evaluate particular submission. Next step is to evaluate given submission and results upload to fileserver. After this worker only send broker that submission was evaluated. More detailed description follows:

• "listening" thread gets multipart message from broker with command "eval"
• "listening" thread hand over whole message through inproc socket to "execution" thread
• "execution" thread now has to prepare all things and get ready for execution
• temporary folders names are initated (but not created) this includes folder with source files, folder with downloaded submission, temporary directory for all possible types of files and folder which will contain results from execution
• if some of the above stated folders is already existing, then it's deleted
• after successfull initiation submission archive is downloaded to created folder
• submission archive is decompressed into submission files folder
• all files from decompressed archive are copied into evaluation directory which can be used for execution in sandboxes
• all other folders which were not created are created just now
• it's time to build job from configuration
• job configuration file is located in evaluation directory if exists and is loaded using yaml-cpp library
• loaded configuration is now parsed into job_metadata structure which is handed over to job execution class itself
• job execution class will now initialize and construct particular tasks from job_metadata into task tree
• if there is some item which can use variables (e.g. binary path, cmd arguments, bound directories) it is done at this point
• all tasks from configuration are created and divided into external or internal tasks
  • external tasks have to load limits from configuration for this workers hwgroup which was loaded from worker configuration
    • if limits were not defined default worker limits are loaded
  • internal tasks are just created without any further processing like external tasks
• after successfull creation of all tasks, they are connected into graph structure using dependencies
• next and last step of building job structure is to execute topological sorting and get queue of tasks which will be executed in order
• topological sorting take into account priority of tasks and sequential order from job configuration
• running all tasks in order follows
• after that results have to be obtained from all executed tasks and given into corresponding yaml file
• result yaml file alongside with content of result folder is sent back to fileserver in compressed form
• of course there has to be cleaning after whole evaluation which will deinitialize all needed variables and also delete all used temporary folders
• all of previous was in "execution" thread which now have to tell "listening" thread that execution is done
• this is done through multipart message "done" with packed job identification addressed to "listening" thread
• action of "listening" is now pretty straightforward "done" message is resend to broker

Broker

Broker gets done message from worker and basically only mark submission as done in its internal structures. No messages are send to web application, because of lazy evaluation on frontend side. More detailed description follows:

• broker gets "done" message from worker after successfull execution of job
• appropriate worker structure is found based on its identification
• some checks of invariants (current job identification, right amount of arguments) are executed
• deletion of current execution request in worker structure follows and appropriate worker is now considered free
• if worker execution queue is not empty than next waiting request is taken and given as current one
  • after that only missing thing is to send that request to worker and loop back to worker execution
• if worker queue is empty then appropriate worker remains free and waiting for another execution request

Web Application

Only remaining part is evaluation of results. This is provided on demand when user wants them. Results are obtained from fileserver and evaluated. More detailed description follows:

• evaluation of execution results is provided on user demand
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