Issue 20219 - Idle D programs keep consuming CPU in Gcx.scanBackground

[rainers]

background scan threads now wait indefinitely, with termination continuously triggering the condition until all threads have woken up

[dlang-bot]

Thanks for your pull request, @rainers!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20219	regression	Idle D programs keep consuming CPU in Gcx.scanBackground

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "stable + druntime#2802"

[thewilsonator]

1. Does this fix this issue? If so the commit title needs to reflect that.
2. should this target stable?
3. I assume it is imposible to test this?

[rainers]

• Does this fix this issue? If so the commit title needs to reflect that.

Oops, missed to add "fix" when copying the title from the issue. Amended.

• should this target stable?

I guess the next version (2.089) will start from master anyway. Or are we already past that point?

• I assume it is imposible to test this?

All the existing tests run with the parallel marking, so the test for correct termination should be that the test suite doesn't run longer than before. Actually testing whether there are too many spurious wake ups of the background threads might be a bit invasive.

[thewilsonator]

Amended.

Thanks.

Or are we already past that point?

not sure, but targeting stable will make it into the betas if nothing else. I only asked because this is marked regression.

Actually testing whether there are too many spurious wake ups of the background threads might be a bit invasive

Thats what I though was going to be the case.

[CyberShadow]

Thank you!

Is the Buildkite Ocean failure related?

[rainers]

Is the Buildkite Ocean failure related?

Maybe. Both failing tests are using fork()...

[CyberShadow]

Speaking of fork, how is it handled by the new GC? It would need to detect it (using atfork) and manually start its own copy of the threads, right? It doesn't seem like it does that currently...

[CyberShadow]

Speaking of fork, how is it handled by the new GC?

I tried it and here's what I found:
https://issues.dlang.org/show_bug.cgi?id=20227

[rainers]

Rebased to stable to pick up #2805