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8275950: Use only _thread_in_vm in ~ThreadBlockInVMPreprocess() #6120

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@pchilano pchilano commented Oct 26, 2021

Please review this small change. Since _thread_in_vm is already an unsafe state there is no need to use the intermediate _thread_blocked_trans state when transitioning back in ~ThreadBlockInVMPreprocess(). Tested tiers1-3 in mach5.

Thanks,
Patricio


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  • JDK-8275950: Use only _thread_in_vm in ~ThreadBlockInVMPreprocess()

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👋 Welcome back pchilanomate! 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.

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@openjdk openjdk bot commented Oct 26, 2021

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

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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.

@openjdk openjdk bot added the hotspot-runtime label Oct 26, 2021
@pchilano pchilano marked this pull request as ready for review Oct 26, 2021
@openjdk openjdk bot added the rfr label Oct 26, 2021
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@mlbridge mlbridge bot commented Oct 26, 2021

Webrevs

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@dholmes-ora dholmes-ora left a comment

Hi Patricio,

This change seems fine.

I note that there are only two callers to is_a_block_safe_state:

  • SafepointSynchronize::block
  • SafepointMechanism::process

but SafepointSynchronize::block is itself now only called from SafepointMechanism::process, so we don't the assert of is_a_block_safe_state in SafepointSynchronize::block.

Thanks,
David

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@openjdk openjdk bot commented Oct 27, 2021

@pchilano 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:

8275950: Use only _thread_in_vm in ~ThreadBlockInVMPreprocess()

Reviewed-by: dholmes, dcubed

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 70 new commits pushed to the master branch:

  • 4ac8403: 8276218: JFR: Clean up jdk.jfr.dcmd
  • 89ade1d: 8273416: C2: assert(false) failed: bad AD file after JDK-8252372 with UseSSE={0,1}
  • dbf5100: 8276201: Shenandoah: Race results degenerated GC to enter wrong entry point
  • 5bb1992: 8275868: ciReplay: Inlining fails with "unloaded signature classes" due to wrong protection domains
  • 158831e: 8274320: os::fork_and_exec() should be using posix_spawn
  • bf2e9ee: 8275080: G1CollectedHeap::expand() returns the wrong value
  • b7104ba: 8196017: java/awt/Mouse/GetMousePositionTest/GetMousePositionWithPopup.java fails
  • 6875678: 8273831: PrintServiceLookup spawns 2 threads in the current classloader, getting orphaned
  • 5bbc8d3: 8274621: NullPointerException because listenAddress[0] is null
  • 5021a12: 8274855: vectorapi tests failing with assert(!vbox->is_Phi()) failed
  • ... and 60 more: https://git.openjdk.java.net/jdk/compare/71d593ede6e1d0a50798d4ba6bfbd78aa65ae7d8...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.

@openjdk openjdk bot added the ready label Oct 27, 2021
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@pchilano pchilano commented Oct 27, 2021

Hi Patricio,

This change seems fine.

I note that there are only two callers to is_a_block_safe_state:

  • SafepointSynchronize::block
  • SafepointMechanism::process

but SafepointSynchronize::block is itself now only called from SafepointMechanism::process, so we don't the assert of is_a_block_safe_state in SafepointSynchronize::block.

Right. I removed the extra assert.

Thanks for the review David!

Patricio

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@dcubed-ojdk dcubed-ojdk left a comment

Thumbs up! I have only a minor comment nit.

If I didn't know any better, I would think you're trying to remove the
whole concept of "transition" states. :-)

// Change to transition state and ensure it is seen by the VM thread.
_thread->set_thread_state_fence(_thread_blocked_trans);
_thread->set_thread_state_fence(_thread_in_vm);
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@dcubed-ojdk dcubed-ojdk Nov 1, 2021

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The comment on L231 is now wrong since you're no longer using
a "transition" state. Perhaps, "Change to an unsafe state..."

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@pchilano pchilano Nov 1, 2021

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Fixed.

@@ -706,7 +706,6 @@ void SafepointSynchronize::block(JavaThread *thread) {
}

JavaThreadState state = thread->thread_state();
assert(is_a_block_safe_state(state), "Illegal threadstate encountered: %d", state);
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Getting rid of this assert makes me a bit nervous, but I have to
get used to the fact that @pchilano is making the safepointing
sub-system simpler and simpler...

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I thought about keeping it but not only we have a single caller(SafepointMechanism::process()) which already has that assert as a guarantee, but also there is no way to add new callers without basically copying all the logic from SafepointMechanism::process() since we cannot just call SS::block().

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@pchilano pchilano commented Nov 1, 2021

Thumbs up! I have only a minor comment nit.

If I didn't know any better, I would think you're trying to remove the whole concept of "transition" states. :-)

Yes, for these cases they add unnecessary additional changes of state. : )

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@pchilano pchilano commented Nov 1, 2021

Thanks for the review Dan!

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@dcubed-ojdk dcubed-ojdk left a comment

Thanks for fixing the comment and for the additional clarifications.

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@pchilano pchilano commented Nov 1, 2021

/integrate

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@openjdk openjdk bot commented Nov 1, 2021

Going to push as commit f55e68c.
Since your change was applied there have been 70 commits pushed to the master branch:

  • 4ac8403: 8276218: JFR: Clean up jdk.jfr.dcmd
  • 89ade1d: 8273416: C2: assert(false) failed: bad AD file after JDK-8252372 with UseSSE={0,1}
  • dbf5100: 8276201: Shenandoah: Race results degenerated GC to enter wrong entry point
  • 5bb1992: 8275868: ciReplay: Inlining fails with "unloaded signature classes" due to wrong protection domains
  • 158831e: 8274320: os::fork_and_exec() should be using posix_spawn
  • bf2e9ee: 8275080: G1CollectedHeap::expand() returns the wrong value
  • b7104ba: 8196017: java/awt/Mouse/GetMousePositionTest/GetMousePositionWithPopup.java fails
  • 6875678: 8273831: PrintServiceLookup spawns 2 threads in the current classloader, getting orphaned
  • 5bbc8d3: 8274621: NullPointerException because listenAddress[0] is null
  • 5021a12: 8274855: vectorapi tests failing with assert(!vbox->is_Phi()) failed
  • ... and 60 more: https://git.openjdk.java.net/jdk/compare/71d593ede6e1d0a50798d4ba6bfbd78aa65ae7d8...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot closed this Nov 1, 2021
@openjdk openjdk bot added integrated and removed ready rfr labels Nov 1, 2021
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@pchilano Pushed as commit f55e68c.

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

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