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/* Copyright (c) 2003, Roger Dingledine
* Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
* Copyright (c) 2007-2021, 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) */
/**
* Initialize the "wallclock" subsystem by setting the current cached time.
**/
static int
subsys_wallclock_initialize(void)
{
update_approx_time(time(NULL));
return 0;
}
/**
* Subsystem function table describing the "wallclock" subsystem.
**/
const subsys_fns_t sys_wallclock = {
.name = "wallclock",
SUBSYS_DECLARE_LOCATION(),
.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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