src/lib/wallclock/approx_time.c

   1 /* Copyright (c) 2003, Roger Dingledine
   2  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
   3  * Copyright (c) 2007-2019, The Tor Project, Inc. */
   4 /* See LICENSE for licensing information */
   5
   6 /**
   7  * \file approx_time.c
   8  * \brief Cache the last result of time(), for performance and testing.
   9  **/
  10
  11 #include "orconfig.h"
  12 #include "lib/wallclock/approx_time.h"
  13
  14 /* =====
  15  * Cached time
  16  * ===== */
  17
  18 #ifndef TIME_IS_FAST
  19 /** Cached estimate of the current time.  Updated around once per second;
  20  * may be a few seconds off if we are really busy.  This is a hack to avoid
  21  * calling time(NULL) (which not everybody has optimized) on critical paths.
  22  */
  23 static time_t cached_approx_time = 0;
  24
  25 /** Return a cached estimate of the current time from when
  26  * update_approx_time() was last called.  This is a hack to avoid calling
  27  * time(NULL) on critical paths: please do not even think of calling it
  28  * anywhere else. */
  29 time_t
  30 approx_time(void)
  31 {
  32   return cached_approx_time;
  33 }
  34
  35 /** Update the cached estimate of the current time.  This function SHOULD be
  36  * called once per second, and MUST be called before the first call to
  37  * get_approx_time. */
  38 void
  39 update_approx_time(time_t now)
  40 {
  41   cached_approx_time = now;
  42 }
  43 #endif /* !defined(TIME_IS_FAST) */