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Remove NodeState::{Waiting,Done} #66405

Merged
merged 5 commits into from
Dec 13, 2019
Merged

Remove NodeState::{Waiting,Done} #66405

merged 5 commits into from
Dec 13, 2019

Commits on Dec 12, 2019

  1. Remove NodeState::{Waiting,Done}. 

    `NodeState` has two states, `Success` and `Done`, that are only used
within `ObligationForest` methods. This commit removes them, and renames
the existing `Waiting` state as `Success`.

We are left with three states: `Pending`, `Success`, and `Error`.
`Success` is augmented with a new `WaitingState`, which indicates when
(if ever) it was last waiting on one or more `Pending` nodes. This
notion of "when" requires adding a "process generation" to
`ObligationForest`; it is incremented on each call to
`process_obligtions`.

This commit is a performance win.

- Most of the benefit comes from `mark_as_waiting` (which the commit
  renames as `mark_still_waiting_nodes`). This function used to do two
  things: (a) change all `Waiting` nodes to `Success`, and (b) mark all
  nodes that depend on a pending node as `Waiting`. In practice, many
  nodes went from `Waiting` to `Success` and then immediately back to
  `Waiting`. The use of generations lets us skip step (a).

- A smaller benefit comes from not having to change nodes to the `Done`
  state in `process_cycles`.
    @nnethercote
    nnethercote committed Dec 12, 2019
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  2. Move functions around. 

    In particular, it has bugged me for some time that `process_cycles` is
currently located before `mark_still_waiting_nodes` despite being called
afterwards.
    @nnethercote
    nnethercote committed Dec 12, 2019
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  3. Remove some debug! statements. 

    Because I am tired of looking at them.
    @nnethercote
    nnethercote committed Dec 12, 2019
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  4. Remove an unnecessary local variable.

    @nnethercote
    nnethercote committed Dec 12, 2019
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  5. Avoid re-processing nodes in find_cycles_from_node.

    @nnethercote
    nnethercote committed Dec 12, 2019
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