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- /* Copyright (c) 2003, Roger Dingledine
- * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
- * Copyright (c) 2007-2019, The Tor Project, Inc. */
- /* See LICENSE for licensing information */
- /**
- * \file approx_time.c
- * \brief Cache the last result of time(), for performance and testing.
- **/
- #include "orconfig.h"
- #include "lib/subsys/subsys.h"
- #include "lib/wallclock/approx_time.h"
- #include "lib/wallclock/wallclock_sys.h"
- /* =====
- * Cached time
- * ===== */
- #ifndef TIME_IS_FAST
- /** Cached estimate of the current time. Updated around once per second;
- * may be a few seconds off if we are really busy. This is a hack to avoid
- * calling time(NULL) (which not everybody has optimized) on critical paths.
- */
- static time_t cached_approx_time = 0;
- /** Return a cached estimate of the current time from when
- * update_approx_time() was last called. This is a hack to avoid calling
- * time(NULL) on critical paths: please do not even think of calling it
- * anywhere else. */
- time_t
- approx_time(void)
- {
- return cached_approx_time;
- }
- /** Update the cached estimate of the current time. This function SHOULD be
- * called once per second, and MUST be called before the first call to
- * get_approx_time. */
- void
- update_approx_time(time_t now)
- {
- cached_approx_time = now;
- }
- #endif /* !defined(TIME_IS_FAST) */
- static int
- subsys_wallclock_initialize(void)
- {
- update_approx_time(time(NULL));
- return 0;
- }
- const subsys_fns_t sys_wallclock = {
- .name = "wallclock",
- .supported = true,
- /* Approximate time is a diagnostic feature, we want it to init right after
- * low-level error handling. */
- .level = -98,
- .initialize = subsys_wallclock_initialize,
- };
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