tdf#130795 use concurrent hashmap in SharedStringPool

we are loading a spreadsheet in parallel here, but the parallel threads
achievei very little actual concurrency because of heavy contention
in the SharedStringPool mutex.

So switch to a concurrent hash map. I looked at a couple of different
ones (including the Folly one), and this was the one with the simplest
resulting code.

This takes my load time from 12.5s to 8s

Change-Id: I04d6d8e11d613b510eb3bc981f3338819b7ac813
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/121717
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

0 files changed, 0 insertions, 0 deletions