RFR: 8280438: Improve BufferNode::Allocator::release to avoid walking pending list [v2]

[Kim Barrett]

> Please review this change to BufferNode::Allocator::release to avoid needing
> to walk the pending list in preparation for transferring it to the free list.
> We need to have both the head and the tail of the pending list to perform that
> transfer.
> 
> Rather than using a LockFreeStack to accumulate the pending list, we now use a
> bespoke data structure that only supports concurrent additions, since that's
> all we need.  This simplifies the code, and also makes it easy to capture the
> first pushed node as the tail.
> 
> To make the transfer from the pending list to the free list, we double-buffer
> the pending list.  Additions are made to the currently active pending list.  A
> transfer flips which pending list is active, and transfers from the list that
> was just deactivated.  Additions are made in a critical section.  The critical
> section synchronization already performed when transferring now does double
> duty, also synchronizing the pending list flip.
> 
> Testing:
> mach5 tier1-3
> 
> Ran a test with -Xlog:gc,ptrqueue,freelist and verified transfers were
> occurring as expected.

Kim Barrett has updated the pull request incrementally with two additional commits since the last revision:

 - update copyrights
 - change _pending_lists init for compiler bug workaround

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7210/files
  - new: https://git.openjdk.java.net/jdk/pull/7210/files/32133237..70c52abb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7210&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7210&range=00-01

  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7210.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7210/head:pull/7210

PR: https://git.openjdk.java.net/jdk/pull/7210