8195158: Concurrent System.gc() is "upgraded" to stop-the-world System.gc()

[Erik Österlund]

Hi Erik,

Looks good.

Thanks,
/Erik

On 2018-01-17 16:33, Erik Helin wrote:
> Hi all,
>
> this patch fixes the bug 'Concurrent System.gc() is "upgraded" to 
> stop-the-world System.gc()' [0]. The bug occurs when all of the 
> following conditions are true:
> - the heap is full (more strictly, there are no regions available for
>   allocations)
> - the Java program executes System.gc()
> - the flag -XX:+ExplicitGCInvokesConcurrent is set
> If all of the above are true, then G1 will do an initial mark YC and 
> (since 862c41 [1]) "upgrade" the gc to a full GC. This "upgrade" 
> should not happen since the user has explicitly set the flag 
> -XX:+ExplicitGCInvokesConcurrent. Since the heap is full, it is likely 
> that the next allocation will trigger a full GC, but the concurrent 
> marking could also finish quickly and free up memory in the cleanup 
> phase.
>
> Patch:
> http://cr.openjdk.java.net/~ehelin/JDK-8195158/00/index.html
>
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8195158
>
> Testing:
> - newly added regression test
> - hs-tier1, hs-tier2, hs-tier3, hs-tier7 on
>   - Linux x86-64
>   - Mac x86-64
>   - Windows x86-64
>   - Solaris SPARC
>
> Thanks,
> Erik
>
> [0]: https://bugs.openjdk.java.net/browse/JDK-8195158
> [1]: http://hg.openjdk.java.net/jdk/hs/rev/862c41cf1c7f