RFR: 8210857: Allow retiring TLABs and collecting statistics in parallel

[Per Liden]

On 09/18/2018 10:13 PM, Per Liden wrote:
> There is currently no good way of retiring TLABs and collecting their 
> statistics in parallel. The current code for doing this also traverses 
> the thread list twice, which is unnecessary. I propose that we adjust 
> the TLAB API to allow this to be done in parallel, in a single pass.
> 
> A few notes on this patch:
> 
> * The GlobalTLABStats class is restructured into the 
> ThreadLocalAllocStats class to allow for a more flexible way of 
> collected statistics when retiring TLABs (flexible in the sense that it 
> allows for parallel operations).
> 
> * The TLAB API is slightly adjusted. The "make_parsable(bool 
> retire_tlab)" is broken into two functions, "make_parsable()" to just 
> make a TLAB parsable, and "retire(ThreadLocalAllocStats* stats)" to 
> retire and optionally collects statistics.
> 
> * GCs are unaffected by this change, in the sense that they continue to 
> call CollectedHeap::ensure_parsability(). However, all GCs will benefit 
> from now doing a single pass over the thread list instead of two to 
> retire and collect stats.
> 
> * This is the last patch in my series of TLAB related patches. The 
> remaining patches only touch ZGC to actually retire/resize/remap TLABs 
> in parallel.
> 
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8210857
> Webrev: http://cr.openjdk.java.net/~pliden/8210857/webrev.0

Testing: Passed tier{1,2,3,4,5,6} on linux-x86_64 (product and debug)

/Per