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  • Added AsyncCallableTask which makes it possible to use blocking tasks asynchronously. The intention is to use this for tasks that involve blocking IO. Thanks to cheftako for the contribution!


  • Removed vararg methods for Tasks.par and Tasks.seq. In their place we've added type-safe alternatives that take up to 10 tasks. This change is not backward compatible for cases where an array was supplied to the varargs version of Tasks.par and Tasks.seq or where a single task was given to Tasks.par or Tasks.seq.
  • Made JsonTraceDeserializer package private - it is not for public consumption
  • Miscellaneous Javadoc improvements


  • Minor performance improvements.


  • Add visualization support to hide all parent tasks.
  • PromiseListener.onResolved(..) now has the Promise that was completed as a parameter.


  • Trace output now contains relationship of potential parents. A potential parent relationship is defined as a parent task running a child task that has already been completed.
  • Dag visualization now includes:
    • Dash edge between a potential parent to an potential child task.
    • Dash edge between a predecessor to a successor task that has been completed.
    • Solid edge between a potential parent to an potential child sink task.


  • No changes


  • Dist target now includes a tarball for tracevis.
  • Added support for system hidden task with support for visualization. User defined hidden task should use ShallowTrace.setHidden(...).


  • Misc code hygiene improvements


    • Removed Tasks.async. Use BaseTask instead.
    • Renamed Tasks.sync to Tasks.callable.
    • Removed Tasks.value which was only used for test purposes.
    • Removed getStartNanos() and getEndNanos() from Task. Instead use Task.getShallowTrace() which returns a ShallowTrace that contains the getStartNanos() and getEndNanos().
    • Engine creation has changed:
      • Replace: new Engine(taskExecutor, timerExecutor)
      • With: new EngineBuilder() .setTaskExecutor(taskExecutor) .setTimerExecutor(timerExecutor) .build();
    • Engine.awaitTermination(...) provides a mechanism to wait for the engine to shutdown.
  • Visualization improvements / fixes:
    • Table: use a textarea for values
    • Waterfall: use nanosecond precision for laying out bars
    • Don't include value.toString() in task name for value task.
  • Logging
    • We now provide three loggers to collect task information at runtime:
      • com.linkedin.parseq.Engine:all - logs all tasks
      • com.linkedin.parseq.Engine:root - logs root tasks only
      • com.linkedin.parseq.Engine:planClass=xyz - When xyz is a root class it and all of its descendants are logged.
    • We provide two log levels with these loggers:
      • DEBUG - logs task name and result type
      • TRACE - logs task name, result type, and value
  • Added Tasks.seq to support Iterable> as a parameter.
  • Added support for hidden trace to indicate if it should be displayed in the visualization.
  • Added attributes to trace such that additional information can be added.
  • Added TraceBuilder to support customize Trace information.


  • Added support for priorities to Tasks. Task priorities only influence ordering in a particular context.
  • Remove the existing waterfall trace visualization and replace it with a more scalable and interactive javascript visualization.
  • Rename to BaseTask.contextRun(...) and BaseTask.doRun(...) to to better match the method purpose.
  • Replace existing trace printers with javascript based equivalents.
  • Dag trace now includes the start time of the task.
  • Added par(Iterable> tasks) to the Tasks class. The new par(...) will return the result of each of the supplied tasks. The ParTask will fail if any of the executed task fails. Additional methods are available for ParTask:
    • getTasks() for the set of tasks related to ParTask.
    • getSuccessful() to get the values of successfully executed tasks.
  • Updated par(...) to return ParTask.


  • Misc code hygiene improvements


  • Trace improvements

    • Rename TaskTrace to Trace
    • Move JsonTraceCodec to com.linkedin.parseq.trace.codec.json
    • Move trace printers to com.linkedin.parseq.trace.printer
    • More compact JSON serialization for traces:
      • Don't include null or empty fields
      • Render each trace once
      • Set up edges independently of the traces
    • Tasks now use null to indicate no value for startNanos and endNanos
    • Traces are now fully immutable and thread-safe. Use TraceBuilders to create new traces or to copy and edit existing ones.
  • Task construction improvments

    • Remove TaskDefs (use Tasks.action, Tasks.sync, Tasks.async, and new BaseTask()) in their place
    • Added ValueTask - returns a pre-determined value upon execution
    • Remove Named. The Tasks factory methods take a name and Task has a constructor that takes a name. If the empty Task constructor is used then getName() will return the value of toString() unless it has been overridden.


  • Promises and Tasks now take Throwables instead of Exceptions. This provides better interoperability with frameworks like Pegasus and Play.
  • Trace creation has changed:
    • Old: TaskTraces.convertToTaskTrace(trace)
    • New: task.getTrace()
  • Remove/rename "assembler"
    • Move com.linkedin.parseq.assembler.trace to com.linkedin.parseq.trace
    • Move all classes in com.linkedin.parseq.assember to com.linkedin.parseq
    • Rename Assembler to Engine
    • Replace references to "assembler" with "engine"
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