8272160: Avoid using 32-bit counters in CDS code

[matias9927]

There are a handful of counters in CDS code that are int when it would be safer to use size_t. While exploring this I discovered that the _count field in DumpTimeKlassSubGraphInfoTable is unused so it is removed and the one use case replaced with a more accurate value. Verified with tier1-5 tests.

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Progress

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Issue

• JDK-8272160: Avoid using 32-bit counters in CDS code (Enhancement - P4)

Reviewers

• Vladimir Kozlov (@vnkozlov - Reviewer) Review applies to d7e054ff
• Ioi Lam (@iklam - Reviewer)

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[bridgekeeper]

👋 Welcome back matsaave! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

@matias9927 This change now passes all automated pre-integration checks.

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

8272160: Avoid using 32-bit counters in CDS code

Reviewed-by: iklam, kvn

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At the time when this comment was updated there had been 192 new commits pushed to the master branch:

• 8a0c47d: 8371225: Missing release of GDK lock in Java_sun_awt_X11_GtkFileDialogPeer_run()
• 90ccdf2: 8371367: Replace remaining JvmtiJavaThreadEventTransition with JVMTI_JAVA_THREAD_EVENT_CALLBACK_BLOCK
• cad73d3: 8370041: GenShen: Filter young pointers from thread local SATB buffers when only marking old
• ... and 189 more: https://git.openjdk.org/jdk/compare/c25f35205ae4544970bbaca233de8745f8e4e92c...master

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[mlbridge]

Webrevs

• 02: Full - Incremental (51febba1)
• 01: Full - Incremental (d7e054ff)
• 00: Full (26b7b378)

[vnkozlov]

You only changed CountSharedSymbols::_count. Please, adjust RFE's title accordingly.

I am not actually convinced why it is necessary. Can you explain why? What benefits you get with this change.

[iklam]

"%zu" should be used for size_t

[matias9927]

You only changed CountSharedSymbols::_count. Please, adjust RFE's title accordingly.

I am not actually convinced why it is necessary. Can you explain why? What benefits you get with this change.

It's preferable to use size_t for counters so we can avoid having negative counts or overflows. I didn't notice any bugs aside from the one listed in the description but I think it is a good defense in depth strategy to use size_t when possible. The number of oops can potentially be very large so any fields that count oops should be size_t. Other areas in the VM use size_t to could classes as well even though it is unlikely to have more than 2 billion classes.

Additionally, some fields track size should also be size_t as these are values that cannot be negative and could possibly be quite large.

I found more instances of int to change to size_t and added them to this PR.

[vnkozlov]

Thank you for explanation and finding more cases - now the title is correct.

[iklam]

LGTM

[matias9927]

Thanks for the reviews @vnkozlov and @iklam!
/integrate

[openjdk]

Going to push as commit 8796611.
Since your change was applied there have been 192 commits pushed to the master branch:

• 8a0c47d: 8371225: Missing release of GDK lock in Java_sun_awt_X11_GtkFileDialogPeer_run()
• 90ccdf2: 8371367: Replace remaining JvmtiJavaThreadEventTransition with JVMTI_JAVA_THREAD_EVENT_CALLBACK_BLOCK
• cad73d3: 8370041: GenShen: Filter young pointers from thread local SATB buffers when only marking old
• ... and 189 more: https://git.openjdk.org/jdk/compare/c25f35205ae4544970bbaca233de8745f8e4e92c...master

Your commit was automatically rebased without conflicts.

[openjdk]

@matias9927 Pushed as commit 8796611.

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