libCom: Add a High-Resolution Time Provider on MacOS

Since Apple don't support clock_gettime(CLOCK_REALTIME) I added a
new time provider that uses the Mach kernel Clock service to get
nanosecond resolution time.

documentation/RELEASE_NOTES.html

@@ -13,6 +13,16 @@
 
 <!-- Insert new items immediately below here ... -->
 
+<h4>High-Resolution Time Provider on MacOS</h4>
+
+<p>MacOS does not provide the clock_gettime() API with CLOCK_REALTIME that other
+Posix systems implement, so we previously used gettimeofday() to fetch the
+current date & time from the OS. That older routine only provides the time with
+a resolution of 1 microsecond though, whereas clock_gettime() gives results with
+a nanosecond resolution.  This release uses a new MachTime time provider on
+MacOS which uses the Mach Kernel's CALENDAR_CLOCK service to fetch the time, and
+provides nanosecond resolution.</p>
+
 <h4>Time drift in periodic scans</h4>
 
 <p>The implementation of the periodic scan code has been modified to remove

src/libCom/osi/os/Darwin/osdTime.cpp

@@ -0,0 +1,86 @@
+/*************************************************************************\
+* Copyright (c) 2013 UChicago Argonne LLC, as Operator of Argonne
+*     National Laboratory.
+* Copyright (c) 2002 The Regents of the University of California, as
+*     Operator of Los Alamos National Laboratory.
+* EPICS BASE is distributed subject to a Software License Agreement found
+* in file LICENSE that is included with this distribution.
+\*************************************************************************/
+
+#include <stddef.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <mach/mach.h>
+#include <mach/clock.h>
+
+#include "osiSock.h"
+
+#define epicsExportSharedSymbols
+#include "cantProceed.h"
+#include "epicsTime.h"
+#include "generalTimeSup.h"
+
+static clock_serv_t host_clock;
+
+extern "C" {
+static int osdTimeGetCurrent (epicsTimeStamp *pDest)
+{
+    mach_timespec_t mts;
+    struct timespec ts;
+
+    clock_get_time(host_clock, &mts);
+    ts.tv_sec = mts.tv_sec;
+    ts.tv_nsec = mts.tv_nsec;
+    *pDest = epicsTime(ts);
+    return epicsTimeOK;
+}
+} // extern "C"
+
+
+static int timeRegister(void)
+{
+    host_get_clock_service(mach_host_self(), CALENDAR_CLOCK, &host_clock);
+
+    generalTimeCurrentTpRegister("MachTime", \
+        LAST_RESORT_PRIORITY, osdTimeGetCurrent);
+    return 1;
+}
+static int done = timeRegister();
+
+
+int epicsTime_gmtime(const time_t *pAnsiTime, struct tm *pTM)
+{
+    return gmtime_r(pAnsiTime, pTM) ?
+        epicsTimeOK : epicsTimeERROR;
+}
+
+int epicsTime_localtime(const time_t *clock, struct tm *result)
+{
+    return localtime_r(clock, result) ?
+        epicsTimeOK : epicsTimeERROR;
+}
+
+extern "C" epicsShareFunc void
+convertDoubleToWakeTime(double timeout, struct timespec *wakeTime)
+{
+    mach_timespec_t now;
+    struct timespec wait;
+
+    clock_get_time(host_clock, &now);
+
+    if (timeout<0.0)
+        timeout = 0.0;
+    else if(timeout>3600.0)
+        timeout = 3600.0;
+
+    wait.tv_sec  = static_cast< long >(timeout);
+    wait.tv_nsec = static_cast< long >((timeout - (double)wait.tv_sec) * 1e9);
+
+    wakeTime->tv_sec  = now.tv_sec + wait.tv_sec;
+    wakeTime->tv_nsec = now.tv_nsec + wait.tv_nsec;
+    if (wakeTime->tv_nsec >= 1000000000L) {
+        wakeTime->tv_nsec -= 1000000000L;
+        ++wakeTime->tv_sec;
+    }
+}

src/libCom/osi/os/posix/osdTime.cpp

@@ -24,7 +24,7 @@
 
     #define TIME_INIT ClockTime_Init(CLOCKTIME_NOSYNC)
 #else
-    /* Some posix systems like Darwin don't have CLOCK_REALTIME */
+    /* Some posix systems may not have CLOCK_REALTIME */
 
     #define TIME_INIT generalTimeCurrentTpRegister("GetTimeOfDay", \
         LAST_RESORT_PRIORITY, osdTimeGetCurrent)