TaskTree CS23

Session Summary

• Introduction and Demo of the TaskTree from Qt Creator's library of solutions

Session Owners

• Presentation by Jarek
• Minutes taken by Volker

Notes

• Introduction to TaskTree
  • generic Qt-based solution for automatic execution of a set of asynchronous tasks
  • manages execution of tasks

• TaskTree class
  • emits done signal with result
  • executes "recipe" after the task tree has been started

• Recipe
  • a value of type "Group"
  • doesn't do anything on its own
  • encapsulates
    • execution mode (e.g. "sequential", "parallel")
    • workflow policy ("stopOnError")
    • list of tasks
  • Group objects can be nested
  • Tasks can be of type ConcurrentCallTask<ResultType>, using Qt Concurrency types

• Custom tasks, subclassing TaskAdapter<Type>
  • describes how to create an asynchronous task
  • E.g. QTimer, QProcess, ConcurrentCall, NetworkQuery, ...
  • Naming convention: tasks correspond to task class type, e.g. QProcessTask is a TaskAdapter<QProcess>
  • Access task object with task(); reimplement start(), emit done

• Handlers
  • custom tasks constructor takes 2 handler arguments (callables/functors): setup handler, done handler

• Storage<DataType> type provides inter-task data exchange
  • handlers can capture the storage object
  • storage uses a QSharedPointer for the data storage, so capturing by value is ok
  • e.g. done-handler writes result to storage, setup-handler of next task reads data from storage

• Demo time

Discussion

• how to handle errors and clean up after error?
  • Done handler
• any plans for a task graph?
  • No plans
  • Working on repeating tasks, which might be sufficient for task-reuse
• Is there a visual component?
  • Not part of the scope, but there's an example/demo
• monadic APIs
  • might be something worth looking into