8357053: ZGC: Improved utility for ZPageAge

[jsikstro]

Hello,

This RFE improves utility for converting to/from, iterating over and defining structures that are indexed using the ZPageAge type.

Converting to/from ZPageAge and its underlying type (uint8_t, often just uint) is currently done via using static_cast. This works fine because sane values are converted in all use cases. However, to make conversion safer (and also more readable), I propose we add a to_zpageage and a corresponding untype that checks that the conversion is valid. Such conversion methods should be used instead of calling static_cast<uint/ZPageAge>.

We currently define a value called ZPageAgeMax, which is defined as static_cast<uint>(ZPageAge::old). The majority of places that use this value actualy use ZPageAgeMax + 1, which is equivalent to the number of ages. Instead, I propose we define and use a value that represents the number of possible ages, called ZPageAgeCount.

Lastly, to make iterating over ages more accessible, I propose we create an intreface of enum iterators of ZPageAge. This will also create a foundation for generating values that require a ZPageAge in the future. Since the end of the enum iterators are exclusive, I've opted to use the following value as end for the iterators:

constexpr ZPageAge ZPageAgeLastPlusOne = static_cast<ZPageAge>(ZPageAgeCount);

I see us using either this or a sentinel/dummy value at the end of the enum class, but I prefer having a value similar to ZPageAgeLastPlusOne over a dummy value.

Testing:

• Oracle's tier 1-4
• GHA

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
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Issue

• JDK-8357053: ZGC: Improved utility for ZPageAge (Enhancement - P4)

Reviewers

• Stefan Karlsson (@stefank - Reviewer) Review applies to 2ea85308
• Stefan Johansson (@kstefanj - Reviewer)

Contributors

• Axel Boldt-Christmas <aboldtch@openjdk.org>

Reviewing

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[openjdk]

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

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8357053: ZGC: Improved utility for ZPageAge

Co-authored-by: Axel Boldt-Christmas <aboldtch@openjdk.org>
Reviewed-by: sjohanss, stefank

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[jsikstro]

/label remove hotspot
/label add hotspot-gc

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The hotspot label was successfully removed.

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@jsikstro
The hotspot-gc label was successfully added.

[jsikstro]

/contributor add @xmas92

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@jsikstro
Contributor Axel Boldt-Christmas <aboldtch@openjdk.org> successfully added.

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Webrevs

• 07: Full (575593ff)
• 06: Full - Incremental (81428965)
• 05: Full - Incremental (653b4015)
• 04: Full (3243a67a)
• 03: Full - Incremental (2ea85308)
• 02: Full - Incremental (25ddc320)
• 01: Full - Incremental (3e0af5e3)
• 00: Full (baee83e6)

[ky0n]

copyright-year update is missing on at least 2 files

[stefank]

A couple of questions before fully reviewing this?

[stefank]

Looks good but I found a couple nits.

[kstefanj]

Looks really nice. As discussed offline, adding a gtest to make sure that the ranges cover the expected ages could be an additional nice addition.

[jsikstro]

Thank you for the reviews!
/integrate

[openjdk]

Going to push as commit 1c72b35.

[openjdk]

@jsikstro Pushed as commit 1c72b35.

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