TaskTree CS23

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Session Summary

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

Session Owners

  • Presentation by Jarek
  • Minutes taken by Volker


  • 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


  • 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