orca/src/platform/osx_clock.c

/************************************************************//**
*
*	@file: osx_clock.cpp
*	@author: Martin Fouilleul
*	@date: 07/03/2019
*	@revision:
*
*****************************************************************/

#include<math.h> //fabs()
#include<time.h>
#include<sys/time.h>	// gettimeofday()
#include<mach/mach.h>
#include<mach/mach_time.h>
#include<mach/clock.h>
#include<Availability.h> // availability macros

#include<sys/types.h>
#include<sys/sysctl.h>

#include"platform_clock.h"


typedef struct timeval timeval;
typedef struct timespec timespec;

//TODO(martin): measure the actual values of these constants
const f64 OC_CLOCK_FUZZ = 25e-9,		// minimum time to read the clock (s)
          OC_CLOCK_TICK = 25e-9;		// minimum step between two clock readings (s)

static mach_timebase_info_data_t __machTimeBase__ = {1,1};
static u64 __initialTimestamp__ = 0;

static inline u64 OSXGetUptimeNanoseconds()
{
	//NOTE(martin): according to the documentation, mach_absolute_time() does not
	//              increment when the system is asleep
	u64 now = mach_absolute_time();
	now *= __machTimeBase__.numer;
	now /= __machTimeBase__.denom;
	return(now);
}

static inline u64 OSXGetMonotonicNanoseconds()
{
	//NOTE(martin): according to the documentation, OC_CLOCK_MONOTONIC increment monotonically
	//              on systems where OC_CLOCK_MONOTONIC_RAW is present, we may want to use that instead,
	//              because OC_CLOCK_MONOTONIC seems to be subject to frequency changes ?

	#if __MAC_OS_X_VERSION_MIN_REQUIRED >= 101200
		#ifndef CLOCK_MONOTONIC_RAW
			#error "CLOCK_MONOTONIC_RAW not found. Please verify that <time.h> is included from the MacOSX SDK rather than /usr/local/include"
		#else
			return(clock_gettime_nsec_np(CLOCK_MONOTONIC_RAW));
		#endif
	#else
		//TODO(martin): quick and dirty hack is to fallback to uptime,
		//              but we should either only support macos version >= 10.12, or find a proper solution
		return(OSXGetUptimeNanoseconds());
	#endif
}

static const f64 CLK_TIMESTAMPS_PER_SECOND = 4294967296.;  // 2^32 as a double
static const u64 CLK_JAN_1970 = 2208988800ULL;             // seconds from january 1900 to january 1970

void oc_clock_init()
{
	mach_timebase_info(&__machTimeBase__);

	//NOTE(martin): get the date of system boot time
	timeval tv = {0, 0};

	int mib[2] = {CTL_KERN,
		      KERN_BOOTTIME};
	size_t size = sizeof(tv);

	if(sysctl(mib, 2, &tv, &size, 0, 0) == -1)
	{
		oc_log_error("can't read boot time\n");
	}
	//NOTE(martin): convert boot date to timestamp
	__initialTimestamp__ =   (((u64)tv.tv_sec + CLK_JAN_1970) << 32)
			       + (u64)(tv.tv_usec * 1e-6 * CLK_TIMESTAMPS_PER_SECOND);

	//TODO(martin): maybe get a state vector for exclusive clock usage ?
	//RandomSeedFromDevice();
}

u64 oc_clock_timestamp(oc_clock_kind clock)
{
	u64 ts = 0;
	switch(clock)
	{
		case OC_CLOCK_MONOTONIC:
		{
			//NOTE(martin): compute monotonic offset and add it to bootup timestamp
			u64 noff = OSXGetMonotonicNanoseconds() ;
			u64 foff = (u64)(noff * 1e-9 * CLK_TIMESTAMPS_PER_SECOND);
			ts = __initialTimestamp__ + foff;
		} break;

		case OC_CLOCK_UPTIME:
		{
			//TODO(martin): maybe we should warn that this date is inconsistent after a sleep ?
			//NOTE(martin): compute uptime offset and add it to bootup timestamp
			u64 noff = OSXGetUptimeNanoseconds() ;
			u64 foff = (u64)(noff * 1e-9 * CLK_TIMESTAMPS_PER_SECOND);
			ts = __initialTimestamp__ + foff;
		} break;

		case OC_CLOCK_DATE:
		{
			//NOTE(martin): get system date and convert it to a fixed-point timestamp
			timeval tv;
			gettimeofday(&tv, 0);
			ts = (((u64)tv.tv_sec + CLK_JAN_1970) << 32)
			        + (u64)(tv.tv_usec * 1e-6 * CLK_TIMESTAMPS_PER_SECOND);
		} break;
	}

	/*
	//NOTE(martin): add a random fuzz between 0 and 1 times the system fuzz
	//TODO(martin): ensure that we always return a value greater than the last value
	f64 fuzz = RandomU32()/(f64)(~(0UL)) * OC_CLOCK_FUZZ;
	ts_timediff tdfuzz = TimediffFromSeconds(fuzz);
	ts = TimestampAdd(ts, tdfuzz);
	*/

	return(ts);
}


f64 oc_clock_time(oc_clock_kind clock)
{
	switch(clock)
	{
		case OC_CLOCK_MONOTONIC:
		{
			//NOTE(martin): compute monotonic offset and add it to bootup timestamp
			u64 noff = OSXGetMonotonicNanoseconds();
			return((f64)noff * 1e-9);
		} break;

		case OC_CLOCK_UPTIME:
		{
			//TODO(martin): maybe we should warn that this date is inconsistent after a sleep ?
			//NOTE(martin): compute uptime offset and add it to bootup timestamp
			u64 noff = OSXGetUptimeNanoseconds();
			return((f64)noff * 1e-9);
		} break;

		case OC_CLOCK_DATE:
		{
			//TODO(martin): maybe warn about precision loss ?
			//              could also change the epoch since we only promise to return a relative time
			//NOTE(martin): get system date and convert it to seconds
			timeval tv;
			gettimeofday(&tv, 0);
			return(((f64)tv.tv_sec + CLK_JAN_1970) + ((f64)tv.tv_usec * 1e-6));
		} break;
	}
}