RFR: 8205022: ZGC: SoftReferences not always cleared before throwing OOME

[Stefan Karlsson]

Looks good.

StefanK

On 2018-06-14 11:42, Per Liden wrote:
> The spec says "All soft references to softly-reachable objects are 
> guaranteed to have been cleared before the virtual machine throws an 
> OutOfMemoryError".
> 
> We currently have a window/race in ZGC, where we can throw OOME before 
> clearing all SoftReferences with a softly-reachable referent. The reason 
> is that the current logic only guarantees that we wait with throwing 
> OOME until the allocating thread have been part of a complete GC cycle, 
> but there is no guarantee that the last GC cycle also cleared 
> SoftReferences.
> 
> This race is causing rare/intermittent failures in tier2 testing 
> (TestSoftRerencesBahviorOnOOME).
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8205022
> Webrev: http://cr.openjdk.java.net/~pliden/8205022/webrev.0/
> 
> Testing: tier{1,2,3,4}
> 
> /Per