Implement clock_gettime using mach_absolute_time

src/butil/time.h

@@ -27,30 +27,47 @@
 #ifdef __MACH__
 #include <mach/clock.h>
 #include <mach/mach.h>
+#include <mach/mach_time.h>
 
 # ifndef clock_gettime
 # define CLOCK_REALTIME CALENDAR_CLOCK
 # define CLOCK_MONOTONIC SYSTEM_CLOCK
 
+#include <pthread.h>
+#include <stdlib.h>                           // exit
+
 typedef int clockid_t;
+
+static mach_timebase_info_data_t timebase;
+static timespec inittime;
+static uint64_t initticks;
+
+static pthread_once_t init_clock_once = PTHREAD_ONCE_INIT;
+static void InitClock() {
+    if (mach_timebase_info(&timebase) != 0) {
+        exit(1);
+    }
+    timeval micro;
+    if (gettimeofday(&micro, NULL) != 0) {
+        exit(1);
+    }
+    inittime.tv_sec = micro.tv_sec;
+    inittime.tv_nsec = micro.tv_usec * 1000L;
+    initticks = mach_absolute_time();
+}
+
 // clock_gettime is not available in MacOS < 10.12
 inline int clock_gettime(clockid_t id, timespec* time) {
-    if (id == CLOCK_MONOTONIC) {
-        clock_serv_t cclock;
-        mach_timespec_t mts;
-        host_get_clock_service(mach_host_self(), id, &cclock);
-        clock_get_time(cclock, &mts);
-        mach_port_deallocate(mach_task_self(), cclock);
-        time->tv_sec = mts.tv_sec;
-        time->tv_nsec = mts.tv_nsec;
-    } else if (id == CLOCK_REALTIME) {
-        struct timeval now;
-        if (gettimeofday(&now, NULL) < 0) {
-            return -1;
-        }
-        time->tv_sec = now.tv_sec;
-        time->tv_nsec = now.tv_usec * 1000;
+    if (pthread_once(&init_clock_once, InitClock) != 0) {
+        exit(1);
     }
+    uint64_t clock = mach_absolute_time() - initticks;
+    uint64_t elapsed = clock * (uint64_t)timebase.numer / (uint64_t)timebase.denom;
+    *time = inittime;
+    time->tv_sec += elapsed / 1000000000L;
+    time->tv_nsec += elapsed % 1000000000L;
+    time->tv_sec += time->tv_nsec / 1000000000L;
+    time->tv_nsec = time->tv_nsec % 1000000000L;
     return 0;
 }
 # endif