http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59439
Bug ID: 59439
Summary: std::locale uses atomic instructions on construction
Product: gcc
Version: 4.8.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: ben.maurer at gmail dot com
In a large multithreaded program that uses stringstream to stringify integers,
I have seen that construction and deconstruction of std::locale can take over
10% of the runtime according to the perf tool.
In bug 40088, std::locale was optimized to avoid the usage of a mutex when
creating the default locale. In our program, this path is being exercised.
However, the act of doing ref counting still has a very large performance
penalty on SMP systems due to cache line bouncing.
If this locale is truly readonly, it would be much better if refcounting could
be avoided. Maybe a refcount of -1 could signify "this object need not be
refcounted".
