JDK-8280002: jmap -histo may leak stream

[tstuefe]

Very trivial fix to a handle/memory leak.

JDK-8215624 added parallel heap iteration to both jmap -histo and jcmd GC.class_histogram. When called with an explicit file and an invalid argument for number of threads, it leaks the file (bit of memory and a handle).

Reproduce with:

jmap -histo:parallel=notanumber,file=xx.txt

Can only be reproduced with jmap. jcmd is safe, arguments are handled correctly in shared code.

---

Progress

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Issue

• JDK-8280002: jmap -histo may leak stream

Reviewers

• Aleksey Shipilev (@shipilev - Reviewer) ⚠️ Review applies to 4d27428
• Serguei Spitsyn (@sspitsyn - Reviewer)

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/7078/head:pull/7078
$ git checkout pull/7078

Update a local copy of the PR:
$ git checkout pull/7078
$ git pull https://git.openjdk.java.net/jdk pull/7078/head

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Checkout this PR locally:
$ git pr checkout 7078

View PR using the GUI difftool:
$ git pr show -t 7078

Using diff file

Download this PR as a diff file:
https://git.openjdk.java.net/jdk/pull/7078.diff

[bridgekeeper]

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[openjdk]

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[mlbridge]

Webrevs

• 01: Full - Incremental (8fd4856d)
• 00: Full (4d27428d)

[shipilev]

This is not as trivial, AFAICS. Note that the existing code delete fs after checking if (os != NULL && os != out). Does it mean this patch can effectively delete out? Or can it call delete nullptr?

[tstuefe]

This is not as trivial, AFAICS. Note that the existing code delete fs after checking if (os != NULL && os != out). Does it mean this patch can effectively delete out?

Thanks for looking at this. No, it is safe.

fs is a temporary fileStream which may or may not be NULL. It is safe to delete it. The delete you mention could be moved out of the condition and it would still be fine. The condition is only really needed for the output which should only appear if you don't write to stdout.

[shipilev]

Okay then!

[openjdk]

@tstuefe 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:

8280002: jmap -histo may leak stream

Reviewed-by: shade, sspitsyn

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 11 new commits pushed to the master branch:

• fb8fdc0: 8279990: (fs) Awkward verbiage in description of Files.createTempFile(Path,String,String,FileAttribute)
• d9dd485: 8280019: Remove unused code from metaspace
• cf283e2: 8279570: IGV: Add source/destination property for load and store nodes with an associated field
• f180530: 8279918: Fix various doc typos
• ac98b22: 8280028: [BACKOUT] Parallel: More precise boundary in ObjectStartArray::object_starts_in_range
• 61b8944: 8278851: Correct signer logic for jars signed with multiple digestalgs
• 35734ad: 8279545: Buffer overrun in reverse_words of sharedRuntime_x86_64.cpp:3517
• e8f494c: 8279825: JFR: JFCModel shouldn't need FilePermission to read predefined .jfc files
• 9f30ec1: 8278398: jwebserver: Add test to confirm maximum request time
• dd76a28: 8280000: Remove unused CardTable::find_covering_region_containing
• ... and 1 more: https://git.openjdk.java.net/jdk/compare/965c64bca713446e7e513170aa9138a8a5eec5de...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[tstuefe]

Okay then!

Thanks, Alexey!

After your concerns I consider this to be not trivial enough, so I wait for a second reviewer.

[sspitsyn]

Hi Thomas,
Nice catch.
Looks good to me.
Thanks,
Serguei

[tstuefe]

Thanks, @shipilev and @sspitsyn !

/integrate

[openjdk]

Going to push as commit c359c35.
Since your change was applied there have been 11 commits pushed to the master branch:

• fb8fdc0: 8279990: (fs) Awkward verbiage in description of Files.createTempFile(Path,String,String,FileAttribute)
• d9dd485: 8280019: Remove unused code from metaspace
• cf283e2: 8279570: IGV: Add source/destination property for load and store nodes with an associated field
• f180530: 8279918: Fix various doc typos
• ac98b22: 8280028: [BACKOUT] Parallel: More precise boundary in ObjectStartArray::object_starts_in_range
• 61b8944: 8278851: Correct signer logic for jars signed with multiple digestalgs
• 35734ad: 8279545: Buffer overrun in reverse_words of sharedRuntime_x86_64.cpp:3517
• e8f494c: 8279825: JFR: JFCModel shouldn't need FilePermission to read predefined .jfc files
• 9f30ec1: 8278398: jwebserver: Add test to confirm maximum request time
• dd76a28: 8280000: Remove unused CardTable::find_covering_region_containing
• ... and 1 more: https://git.openjdk.java.net/jdk/compare/965c64bca713446e7e513170aa9138a8a5eec5de...master

Your commit was automatically rebased without conflicts.

[openjdk]

@tstuefe Pushed as commit c359c35.

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