Line data    Source code

       1             : /* Copyright (c) 2003, Roger Dingledine
       2             :  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
       3             :  * Copyright (c) 2007-2021, 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/subsys/subsys.h"
      13             : #include "lib/wallclock/approx_time.h"
      14             : #include "lib/wallclock/wallclock_sys.h"
      15             : 
      16             : /* =====
      17             :  * Cached time
      18             :  * ===== */
      19             : 
      20             : #ifndef TIME_IS_FAST
      21             : /** Cached estimate of the current time.  Updated around once per second;
      22             :  * may be a few seconds off if we are really busy.  This is a hack to avoid
      23             :  * calling time(NULL) (which not everybody has optimized) on critical paths.
      24             :  */
      25             : static time_t cached_approx_time = 0;
      26             : 
      27             : /** Return a cached estimate of the current time from when
      28             :  * update_approx_time() was last called.  This is a hack to avoid calling
      29             :  * time(NULL) on critical paths: please do not even think of calling it
      30             :  * anywhere else. */
      31             : time_t
      32      291749 : approx_time(void)
      33             : {
      34      291749 :   return cached_approx_time;
      35             : }
      36             : 
      37             : /** Update the cached estimate of the current time.  This function SHOULD be
      38             :  * called once per second, and MUST be called before the first call to
      39             :  * get_approx_time. */
      40             : void
      41        5933 : update_approx_time(time_t now)
      42             : {
      43        5933 :   cached_approx_time = now;
      44        5933 : }
      45             : #endif /* !defined(TIME_IS_FAST) */
      46             : 
      47             : /**
      48             :  * Initialize the "wallclock" subsystem by setting the current cached time.
      49             :  **/
      50             : static int
      51        5553 : subsys_wallclock_initialize(void)
      52             : {
      53        5553 :   update_approx_time(time(NULL));
      54        5553 :   return 0;
      55             : }
      56             : 
      57             : /**
      58             :  * Subsystem function table describing the "wallclock" subsystem.
      59             :  **/
      60             : const subsys_fns_t sys_wallclock = {
      61             :   .name = "wallclock",
      62             :   SUBSYS_DECLARE_LOCATION(),
      63             :   .supported = true,
      64             :   /* Approximate time is a diagnostic feature, we want it to init right after
      65             :    * low-level error handling. */
      66             :   .level = -98,
      67             :   .initialize = subsys_wallclock_initialize,
      68             : };