8357681: Fixed the DigitList::toString method causing incorrect results during debugging

[wenshao]

When debugging getLong/getDouble/getDecimal of DigitList, the debugger will call the DigitList::toString method. At this time, DigitList::toString will modify tempBuilder, which will cause incorrect results.

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Issue

• JDK-8357681: Fixed the DigitList::toString method causing incorrect results during debugging (Enhancement - P5)

Reviewers

• Justin Lu (@justin-curtis-lu - Committer)
• Naoto Sato (@naotoj - Reviewer)

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[openjdk]

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

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

8357681: Fixed the DigitList::toString method causing incorrect results during debugging

Reviewed-by: jlu, naoto

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At the time when this comment was updated there had been 158 new commits pushed to the master branch:

• c1f066e: 8356888: (fs) FileSystems.newFileSystem that take an env must specify IllegalArgumentException
• c295377: 8357800: Initialize JvmtiThreadState bool fields with bool literals
• cdff7b9: 8357801: Parallel: Remove deprecated PSVirtualSpace methods
• ... and 155 more: https://git.openjdk.org/jdk/compare/76570c627db527f856f2394fb9ead02939eca621...master

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[openjdk]

@wenshao The following label will be automatically applied to this pull request:

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[mlbridge]

Webrevs

• 00: Full (179bd3c4)

[liach]

This change looks reasonable to me. I couldn't find any direct usage of DigitList::toString.

[liach]

/label add i18n

This is a formatting-related class. Calling i18n devs.

[openjdk]

@liach
The i18n label was successfully added.

[justin-curtis-lu]

Change looks good to me, since the previous code causes conflicts where getStringBuilder is called during debugging. Did not see any usages of DigitList.toString() by us as well.

[jdlib]

what about

        return new StringBuilder()
                .append("0.")
                .append(digits, 0, count)
                .append("x10^")
                .append(decimalAt)
                .toString();

to avoid the temporary string created by new String(digits, 0, count)

[wenshao]

Using the String concatenation operator looks cleaner.

In the core library, they are effectively the same, and JEP 280 Indify String Concatenation is not available in the core library.

[naotoj]

LGTM

[vy]

Nit: Would it be an overkill to add a test (verifying toString doesn't spoil the content) to avoid falling on the same slippery slope (i.e., "Let me optimize this by reusing the SB!") again?

[wenshao]

Nit: Would it be an overkill to add a test (verifying toString doesn't spoil the content) to avoid falling on the same slippery slope (i.e., "Let me optimize this by reusing the SB!") again?

The original code that calls getStringBuilder() is this code:

    private StringBuilder tempBuilder;

    private StringBuilder getStringBuilder() {
        if (tempBuilder == null) {
            tempBuilder = new StringBuilder(MAX_COUNT);
        } else {
            tempBuilder.setLength(0);
        }
        return tempBuilder;
    }

This is a concurrency problem, which is triggered during the DEBUG process.

To test this concurrency problem, we need to build a concurrent competition test, which is not a simple task, so I did not add it.

[RogerRiggs]

To test this concurrency problem, we need to build a concurrent competition test, which is not a simple task, so I did not add it.

The label noreg-hard would be appropriate to indicate a test was not created due to difficulty.
That label though conflicts with the current label noreg-trivial implying there is an existing test and the change is not significant. It will look odd, but both labels make sense.
OpenJDK Developers guide

[wenshao]

/integrate

[openjdk]

Going to push as commit b7f0f48.
Since your change was applied there have been 198 commits pushed to the master branch:

• bb2c80c: 8298420: Implement JEP 470: PEM Encodings of Cryptographic Objects (Preview)
• 28f5093: 8356233: NMT: tty->print_cr should not be used in VirtualMemoryTracker::add_reserved_region()
• cd052c7: 8345431: Improve jar --validate to detect duplicate or invalid entries
• ... and 195 more: https://git.openjdk.org/jdk/compare/76570c627db527f856f2394fb9ead02939eca621...master

Your commit was automatically rebased without conflicts.

[openjdk]

@wenshao Pushed as commit b7f0f48.

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