Comment 107 for bug 1684993

Reviewed: https://review.opencontrail.org/46533
Committed: http://github.com/Juniper/contrail-third-party-cache/commit/2bc86f217df73ef1bcdd2c9ad87540cd4f9cb95c
Submitter: Zuul v3 CI (<email address hidden>)
Branch: master

commit 2bc86f217df73ef1bcdd2c9ad87540cd4f9cb95c
Author: Ananth Suryanarayana <email address hidden>
Date: Wed Sep 26 12:03:07 2018 -0700

Do not insert already sleeping tbb task back into sleeping list

During testing, it was found that tbb sleeping threads singly linked
list was corrupted and had become circular. This seemingly caused
my_slack count to get permanently stuck at -1, as the sleeping list
traversal would potentially never end.

During testing, using a specific assert, it was confirmed that duplicate
insertion did happen.

Fixed it by modifying the sleeing threads singly linked list into a
doubly linked list and then making sure that a thread if already in
the list is never prepended back as the head of the list.

https://github.com/01org/tbb/issues/86

Change-Id: Ic0a943b54afa07115ad6f304310d385cb199c504
Closes-Bug: #1684993
Depends-On: I1c08787cf74a12b5486189eb0dc69cd524ed4170
Depends-On: I84993a23b4524f19c42e4166015c9216466c6865