8272811: Document the effects of building with _GNU_SOURCE in os_posix.hpp

[dholmes-ora]

Please review this trivial code documentation enhancement based on discussions here:

http://mail.openjdk.java.net/pipermail/jdk-dev/2021-August/005946.html

Thanks,
David

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Issue

• JDK-8272811: Document the effects of building with _GNU_SOURCE in os_posix.hpp

Reviewers

• Ioi Lam (@iklam - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/5212/head:pull/5212
$ git checkout pull/5212

Update a local copy of the PR:
$ git checkout pull/5212
$ git pull https://git.openjdk.java.net/jdk pull/5212/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 5212

View PR using the GUI difftool:
$ git pr show -t 5212

Using diff file

Download this PR as a diff file:
https://git.openjdk.java.net/jdk/pull/5212.diff

[bridgekeeper]

👋 Welcome back dholmes! 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]

@dholmes-ora The following label will be automatically applied to this pull request:

• hotspot-runtime

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[mlbridge]

Webrevs

• 00: Full (bd7a9653)

[jerboaa]

Shouldn't something along those lines also be mentioned where it's actually defined? Like:

jdk/make/autoconf/flags-cflags.m4

Line 432 in d34f17c

ALWAYS_DEFINES_JVM="-D_GNU_SOURCE -D_REENTRANT"

[iklam]

Looks OK to me, but I think the REF title should use "effects" :-)

[dholmes-ora]

@jerboaa thanks for taking a look. I initially planned to document it in the makefiles somewhere but then found that we don't document why we use any flags there :( Plus there are a number of places where -D_GNU_SOURCE is used and I only want to document the reasoning for the VM which would then beg the question is to why the other uses are not documented somehow. So I just put it in os_posix.hpp where it was more likely to be seen when needed.

[dholmes-ora]

@iklam thanks for taking a look. Hmmmm tricky one. I think you are right. Using -D_GNU_SOURCE affects the build, but we are documenting the results of that and those are the effects of using the flag.

[jerboaa]

@jerboaa thanks for taking a look. I initially planned to document it in the makefiles somewhere but then found that we don't document why we use any flags there :( Plus there are a number of places where -D_GNU_SOURCE is used and I only want to document the reasoning for the VM which would then beg the question is to why the other uses are not documented somehow. So I just put it in os_posix.hpp where it was more likely to be seen when needed.

Fair enough.

[dholmes-ora]

@jerboaa , @iklam again thanks for looking at this, but can someone actually approve it please :) Thanks.

[openjdk]

@dholmes-ora 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:

8272811: Document the effects of building with _GNU_SOURCE in os_posix.hpp

Reviewed-by: iklam

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 34 new commits pushed to the master branch:

• 673ce7e: 8272873: C2: Inlining should not depend on absolute call site counts
• 7212561: 8267188: gc/stringdedup/TestStringDeduplicationInterned.java fails with Shenandoah
• e36cbd8: 8242847: G1 should not clear mark bitmaps with no marks
• 2ef6871: 8272447: Remove 'native' ranked Mutex
• 63e062f: 8236176: Parallel GC SplitInfo comment should be updated for shadow regions
• c5a2712: 8272850: Drop zapping values in the Zap* option descriptions
• 1e3e333: 8272884: Make VoidClosure::do_void pure virtual
• 0f428ca: 8272570: C2: crash in PhaseCFG::global_code_motion
• b17b821: 8272639: jpackaged applications using microphone on mac
• 0e7288f: 8267125: AES Galois CounterMode (GCM) interleaved implementation using AVX512 + VAES instructions
• ... and 24 more: https://git.openjdk.java.net/jdk/compare/b690f29699180149d33b6a83de10697790587a87...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.

[dholmes-ora]

/integrate

[openjdk]

Going to push as commit c4c76e2.
Since your change was applied there have been 34 commits pushed to the master branch:

• 673ce7e: 8272873: C2: Inlining should not depend on absolute call site counts
• 7212561: 8267188: gc/stringdedup/TestStringDeduplicationInterned.java fails with Shenandoah
• e36cbd8: 8242847: G1 should not clear mark bitmaps with no marks
• 2ef6871: 8272447: Remove 'native' ranked Mutex
• 63e062f: 8236176: Parallel GC SplitInfo comment should be updated for shadow regions
• c5a2712: 8272850: Drop zapping values in the Zap* option descriptions
• 1e3e333: 8272884: Make VoidClosure::do_void pure virtual
• 0f428ca: 8272570: C2: crash in PhaseCFG::global_code_motion
• b17b821: 8272639: jpackaged applications using microphone on mac
• 0e7288f: 8267125: AES Galois CounterMode (GCM) interleaved implementation using AVX512 + VAES instructions
• ... and 24 more: https://git.openjdk.java.net/jdk/compare/b690f29699180149d33b6a83de10697790587a87...master

Your commit was automatically rebased without conflicts.

[openjdk]

@dholmes-ora Pushed as commit c4c76e2.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.