Fix for DEV-39442: Increased the performance of LLDate::toHTTPDateString

by over 50 times.

Looking at the usage, toHTTPDateStream is not called anywhere (except
internally by toHTTPDateString), and toHTTPDateString is called only
once outside of lldate.cpp, by LLStringUtil::formatDatetime. Also, the
method is most commonly called with a single two-character token, such
as "%Y" or "%A".

I therefore removed toHTTPDateStream and optimized toHTTPDateString.
Setting the locale was the most expensive operation, so I looked into
caching that, both in terms of std::ostream and strftime. The timings
for those implementations (averaged over 10 calls) is:

toHTTPDateString timings:
 - with ostream (current)                -> 0.314156 ms
 - with ostream and std::locale caching  -> 0.033999 ms
 - with strftime and setlocale() caching -> 0.005985 ms

I therefore went with the standard C library strftime solution.

I also wrote a few unit tests to make sure that I didn't break any
existing functionality, and tested this under Windows and Linux.

Reviewed by steve.

1 files changed, 0 insertions, 1 deletions

diff --git a/indra/llcommon/lldate.h b/indra/llcommon/lldate.h
index 23d3b900f8..9dcce9117f 100644
--- a/indra/llcommon/lldate.h
+++ b/indra/llcommon/lldate.h
@@ -86,7 +86,6 @@ public:
 	void toStream(std::ostream&) const;
 	std::string toHTTPDateString (std::string fmt) const;
 	static std::string toHTTPDateString (tm * gmt, std::string fmt);
-	static void toHTTPDateStream(std::ostream&, tm *, std::string);
 	/** 
 	 * @brief Set the date from an ISO-8601 string.
 	 *