tree 21fd6a8d4a7617f8d0d5202ddeda2cd9a8420128
parent 4d935d5ecad583dd9f87d3b08085145c900e21fb
author ulfjack <ulfjack@google.com> 1550497634 -0800
committer Copybara-Service <copybara-worker@google.com> 1550497835 -0800

Refactor SkyframeActionExecutor

Move all action state tracking to a new subclass, which replaces the
use of Pair+FutureTask, and carefully ensures that we don't hold onto
memory for any longer than necessary.

This is another attempt at preparing for async action execution. A
similar refactoring was previously attempted in https://github.com/bazelbuild/bazel/commit/14f8b109b9f987f1b0c69c8cf399326740749382, but had to
be rolled back as https://github.com/bazelbuild/bazel/commit/68fc46b7ac2a015cbbd4e6602f2310a935783866 due to increased memory consumption.

The new code may seem a bit overengineered given that the current
implementation requires exactly two states:
STARTED -> DONE

However, async actions will have at least three, and possibly more
states, which requires a bit more infrastructure here:
STARTED -> IN_PROGRESS -> DONE

Note that we need to explicitly model the intermediate state such that
parallel threads due to action sharing can see the IN_PROGRESS state,
and register their dependency on the corresponding Future (code in a
subsequent commit).

Progress on #6394.

PiperOrigin-RevId: 234469209