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sealed abstract class FrameIndexRef extends AnyRef

A reference that boxes a FrameIndex possibly using a thread-local.

This definition is of interest only when creating tasks with Task.unsafeCreate, which exposes internals and is considered unsafe to use.

In case the Task is executed with BatchedExecution, this class boxes a FrameIndex in order to transport it over light async boundaries, possibly using a ThreadLocal, since this index is not supposed to survive when threads get forked.

The FrameIndex is a counter that increments whenever a flatMap operation is evaluated. And with BatchedExecution, whenever that counter exceeds the specified threshold, an asynchronous boundary is automatically inserted. However this capability doesn't blend well with light asynchronous boundaries, for example Async tasks that never fork logical threads or TrampolinedRunnable instances executed by capable schedulers. This is why FrameIndexRef is part of the Context of execution for Task, available for asynchronous tasks that get created with Task.unsafeCreate.

Note that in case the execution model is not BatchedExecution then this reference is just a dummy, since there's no point in keeping a counter around, plus setting and fetching from a ThreadLocal can be quite expensive.

Source
Task.scala
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AnyRef, Any
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Abstract Value Members

  1. abstract def :=(update: FrameIndex): Unit

    Stores a new FrameIndex.

  2. abstract def apply(): FrameIndex

    Returns the current FrameIndex.

  3. abstract def reset(): Unit

    Resets the stored FrameIndex to 1, which is the default value that should be used after an asynchronous boundary happened.