8268290: Improve LockFreeQueue<> utility

[kimbarrett]

Please review this change to the LockFreeQueue utility class.

The LockFreeQueue originated as an implementation detail of
G1DirtyCardQueueSet, and was recently refactored into a public utility
class. In that refactoring it retained some limitations that were
acceptable in its original context, but may be problematic as a general
utility.

In particular, under some conditions a thread was not be able to pop the
last element in the queue, due to interference by a concurrent operation.
And this state will persist, so retrying the pop operation won't help until
the interfering thread had made sufficient progress. This was mitigated by
making the API more complex to provide notice to the client that the queue
may be in this state.

But it turns out we can do somewhat better, eliminating one of the
limitations, which is the point of this change. We introduce a
pseudo-object used as an end of queue marker. We can use the transition of
the last element's next value from the end marker to NULL by a pop operation
as a claim on the element, allowing the losing thread to recognize, retry,
and make progress.

This queue still has the limitation that an in-progress push/append may
prevent popping elements. Because of this, the class is being renamed to
NonblockingQueue. The old name suggests stronger guarantees than actually
provided.

The PR has two commits, the first for the functional changes, the second for
the renaming. The github diffs don't seem to be recognizing the renaming of
the source files as a rename, instead treating the old files as deleted and
the new files as added. The first commit by itself is probably more useful
for reviewing the functional changes.

Testing:
mach5 tier1-5

---

Progress

• Change must not contain extraneous whitespace
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Issue

• JDK-8268290: Improve LockFreeQueue<> utility

Reviewers

• Ivan Walulya (@walulyai - Committer) ⚠️ Review applies to 8fe607c
• Thomas Schatzl (@tschatzl - Reviewer) ⚠️ Review applies to 0adb595

Reviewing

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Update a local copy of the PR:
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Using diff file

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https://git.openjdk.java.net/jdk/pull/4379.diff

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[mlbridge]

Webrevs

• 02: Full - Incremental (3710810d)
• 01: Full - Incremental (0adb5954)
• 00: Full (8fe607c3)

[walulyai]

lgtm!

[tschatzl]

I think this is good.

[openjdk]

@kimbarrett This change now passes all automated pre-integration checks.

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8268290: Improve LockFreeQueue<> utility

Reviewed-by: iwalulya, tschatzl

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[kimbarrett]

Thanks @walulyai and @tschatzl for reviews.

[kimbarrett]

/integrate

[openjdk]

Going to push as commit 0c693e2.

[openjdk]

@kimbarrett Pushed as commit 0c693e2.

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[caoman]

Thank you for this fix. I like how append() can just store to &_head on CAS failure.

Minor comments:
Is it recommended to add SpinPause() in pop()'s while loop body?
This sentence above append() in inline.hpp could be removed: "it is an invariant that the old tail's "next" value is NULL".
I can make a PR for these separately.

[walulyai]

Minor comments:
Is it recommended to add SpinPause() in pop()'s while loop body?

I think with a try_pop method, if one needs to have a SpinPause, they can re-implement the retry-loop with the SpinPause and try_pop instead of having this in a generic pop().

[kimbarrett]

I don't think pop() needs SpinPause() in its body. It's not really an empty spin. It only loops on a cmpxchg failure. Someone might want to use try_pop() and SpinYield or something similar in a highly contended case, but I'd rather leave that to the specific case to parameterize.

You are correct that this comment should be removed: "it is an invariant that the old tail's "next" value is NULL". Oops, sorry I missed that.