[Boost-bugs] [Boost C++ Libraries] #11806: microsec_clock::universal_time() is needlessly slow

Subject: [Boost-bugs] [Boost C++ Libraries] #11806: microsec_clock::universal_time() is needlessly slow
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-11-19 15:58:36

#11806: microsec_clock::universal_time() is needlessly slow
------------------------------+--------------------------
 Reporter:  jzwinck@…         |      Owner:  az_sw_dude
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  date_time
  Version:  Boost 1.55.0      |   Severity:  Optimization
 Keywords:                    |
------------------------------+--------------------------
 The
 [http://www.boost.org/doc/libs/1_55_0/doc/html/date_time/posix_time.html

 documentation] for `microsec_clock::universal_time()` says:

 > Get the UTC time using a sub second resolution clock. On Unix systems
 this is implemented using !GetTimeOfDay.

 In fact it is implemented partly using `gettimeofday()` but also
 `gmtime_r()`.  Once you unwrap all the layers, the flow is something like
 this:

     sec,nsec = gettimeofday()
     date,time = gmtime(sec)
     sec,nsec = ptime(date,time)
     return sec+nsec/1000

 The problem is that `gmtime_r()` is very slow, relative to the other
 operations involved here, and it is completely unnecessary.  A call to
 `gettimeofday()` on Unix is all you need to implement `universal_time()`.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11806>
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