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Diffstat (limited to 'lib/qtime.c')
| -rw-r--r-- | lib/qtime.c | 205 |
1 files changed, 205 insertions, 0 deletions
diff --git a/lib/qtime.c b/lib/qtime.c new file mode 100644 index 00000000..42b903da --- /dev/null +++ b/lib/qtime.c @@ -0,0 +1,205 @@ +/* Quagga realtime and monotonic clock handling -- functions + * Copyright (C) 2009 Chris Hall (GMCH), Highwayman + * + * This file is part of GNU Zebra. + * + * GNU Zebra is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published + * by the Free Software Foundation; either version 2, or (at your + * option) any later version. + * + * GNU Zebra is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with GNU Zebra; see the file COPYING. If not, write to the + * Free Software Foundation, Inc., 59 Temple Place - Suite 330, + * Boston, MA 02111-1307, USA. + */ + +#include <sys/times.h> +#include <errno.h> + +#include "zassert.h" +#include "qtime.h" + +/*============================================================================== + * This is a collection of functions and (in qtime.h) macros and inline + * functions which support system time and a monotonic clock. + * + * TODO: introduce mutex for crafted monotonic time, and initialisation + * routine for that: which can preset the various variables... but + * unless is guaranteed to be called, must leave the on-the-fly + * initialisation... could also start a watchdog at that point. + */ + +/*============================================================================== + * Replacement for CLOCK_MONOTONIC. + * + * With thanks to Joakim Tjernlund for reminding everyone of the return value + * from times() ! + * + * times() is defined to return a value which is the time since some fixed time + * before the application started (or when the application started). This time + * is measured in units of sysconf(_SC_CLK_TCK) ticks per second. + * + * The only tricky bit is that the value returned (of type clock_t) is a + * signed integer, which can overflow. It is not defined exactly how it + * does this... This code assumes that the system will wrap around in some + * obvious way. The base of the time for this clock may be when the *system* + * started... so when it overflows may depend on how long the system has been + * up... which suggests that some sensible wrap around is likely (?). + * + * The qtime_t value is in nano-seconds. + * + * The result from times() is in units of sysconf(_SC_CLK_TCK) ticks per second. + * + * If clock_t is a signed 32-bit integer, which is kept +ve, then the clock + * overflows/wraps round in 2^31 ticks which is: + * + * at 100 ticks/sec: > 248 days + * at 1,000 ticks/sec: > 24 days + * at 10,000 ticks/sec: > 59 hours + * + * For safety, this asserts that sysconf(_SC_CLK_TCK) <= 1,000,000 for + * sizeof(clock_t) > 4, but <= 1,000 for sizeof(clock_t) == 4. + * + * (It appears that 60, 100, 250 and 1,000 ticks/sec. are popular options.) + * + * If sizeof(clock_t) > 4, it is assumed large enough never to wrap around. + * + * When clock_t is a 32-bit integer must be at least ready for wrap around. + * There are two cases: + * + * * +ve wrap around. new < old value, and new >= 0 + * + * step = (INT32_MAX - old + 1) + new + * + * * -ve wrap around. new < old value, and new < 0 (and old > 0) + * + * step = (INT32_MAX - old + 1) - (INT32_MIN - new) + * + * In any event, a step > 24 hours is taken to means that something has gone + * very, very badly wrong. + * + * NB: it is assumed that qt_craft_monotonic will be called often enough to + * ensure that the check on the step size will not be triggered ! + * + * NB: it is assumed that times() does not simply stick if it overflows. + * + * TODO: Add a watchdog to monitor the behaviour of this clock ? + */ + +CONFIRM((sizeof(clock_t) >= 4) && (sizeof(clock_t) <= 8)) ; + +#ifdef GNU_LINUX +#define TIMES_TAKES_NULL 1 +#else +#undef TIMES_TAKES_NULL +#endif + +static uint64_t monotonic = 0 ; /* monotonic clock in _SC_CLK_TCK's */ +static int64_t last_times_sample = 0 ; /* last value returned by times() */ + +static uint64_t step_limit = 0 ; /* for sanity check */ + +static int64_t times_clk_tcks = 0 ; /* sysconf(_SC_CLK_TCK) */ +static qtime_t times_scale_q = 0 ; /* 10**9 / times_clk_tcks */ +static qtime_t times_scale_r = 0 ; /* 10**9 % times_clk_tcks */ + +qtime_mono_t +qt_craft_monotonic(void) { + struct tms dummy ; + int64_t this_times_sample ; + uint64_t step ; + + /* Set up times_scale_q & times_scale_q if not yet done. */ + if (times_clk_tcks == 0) /* Is zero until it's initialized */ + { + lldiv_t qr ; + confirm(sizeof(qtime_t) <= sizeof(long long int)) ; + + times_clk_tcks = sysconf(_SC_CLK_TCK) ; + passert((times_clk_tcks > 0) && + (times_clk_tcks <= (sizeof(clock_t) > 4) ? 1000000 + : 1000)) ; + + qr = lldiv(QTIME_SECOND, times_clk_tcks) ; + times_scale_q = qr.quot ; + times_scale_r = qr.rem ; + + step_limit = (uint64_t)24 * 60 * 60 * times_clk_tcks ; + } ; + + /* No errors are defined for times(), but a return of -1 is defined */ + /* to indicate an error condition, with errno saying what it is ! */ + /* */ + /* The following deals carefully with this -- cannot afford for the */ + /* clock either to jump or to get stuck ! */ + +#ifdef TIMES_TAKES_NULL + this_times_sample = times(NULL) ; /* assume this saves effort ! */ +#else + this_times_sample = times(&dummy) ; +#endif + + if (this_times_sample == -1) /* deal with theoretical error */ + { + errno = 0 ; + this_times_sample = times(&dummy) ; + if (errno != 0) + zabort_errno("times() failed") ; + } ; + + /* Calculate the step and verify sensible. */ + /* */ + /* Watch out for huge jumps and/or time going backwards. */ + /* For 32-bit clock_t, look out for wrap-around. */ + + if ((sizeof(clock_t) > 4) || (this_times_sample > last_times_sample)) + /* time going backwards will appear as HUGE step forwards. */ + step = (uint64_t)(this_times_sample - last_times_sample) ; + else + { + if (this_times_sample > 0) + /* both samples +ve => +ve wrap around. */ + step = (uint64_t)( ((int64_t)INT32_MAX - last_times_sample + 1) + + this_times_sample ) ; + else + /* this sample -ve and last sample +ve => -ve wrap round */ + /* this sample -ve and last sample -ve => time gone backwards */ + /* (which appears as a HUGE step forwards). */ + step = (uint64_t)( ((int64_t)INT32_MAX - last_times_sample + 1) + - ((int64_t)INT32_MIN - this_times_sample) ) ; + } ; + + /* TODO: better error messaging for large clock jumps. */ + if (step > step_limit) + zabort("Sudden large monotonic clock jump") ; + + /* Advance the monotonic clock in sysconf(_SC_CLK_TCK) units. */ + monotonic += step ; + + /* Remember what we got, for next time. */ + last_times_sample = this_times_sample ; + + /* Scale to qtime_t units. */ + if (times_scale_r == 0) + return monotonic * times_scale_q ; + else + return (monotonic * times_scale_q) + + ((monotonic * times_scale_r) / times_clk_tcks) ; +} ; + +/*------------------------------------------------------------------------------ + * Get crafted monotonic time -- in seconds + */ +extern time_t +qt_craft_mono_secs(void) +{ + qt_craft_monotonic() ; /* update the monotonic counter */ + + return monotonic / times_clk_tcks ; +} ; |