[vlc-devel] [PATCH 1/3] compat: add clock_gettime for darwin

[Marvin Scholz]

---
 compat/clock_gettime.c | 130 +++++++++++++++++++++++++++++++++++++++++
 configure.ac           |   4 ++
 include/vlc_fixups.h   |  11 ++++
 3 files changed, 145 insertions(+)
 create mode 100644 compat/clock_gettime.c

diff --git a/compat/clock_gettime.c b/compat/clock_gettime.c
new file mode 100644
index 0000000000..dbe2434d9d
--- /dev/null
+++ b/compat/clock_gettime.c
@@ -0,0 +1,130 @@
+/*****************************************************************************
+ * clock_gettime.c: POSIX clock_gettime() replacement
+ *****************************************************************************
+ * Copyright © 2020 VLC authors and VideoLAN
+ *
+ * Author: Marvin Scholz <epirat07 at gmail dot com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifndef __APPLE__
+# error clock_gettime not implemented on your platform!
+#endif
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#define _DARWIN_C_SOURCE
+#define _POSIX_C_SOURCE  200809L
+
+#include <sys/errno.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <sys/sysctl.h>
+
+/**
+ * Get the absolute time at which the system was booted
+ * 
+ * This time is changed whenever the clock is adjusted to
+ * correctly reflect the boot time with the adjusted clock,
+ * so just querying it once and reusing the value is not safe.
+ *
+ * \param[out]  tv   Timeval struct to write the boottime to
+ * 
+ * \note
+ * The boot time only has microsecond precision
+ *
+ * \return 0 on success, else -1 and errno set
+ */
+static int vlc__get_system_boottime(struct timeval *tv)
+{
+    int ret = sysctl((int[]){ CTL_KERN, KERN_BOOTTIME }, 2,
+                     tv, &(size_t){ sizeof(*tv) }, NULL, 0);
+
+    if (ret != 0)
+        return errno;
+
+    return 0;
+}
+
+/**
+ * Get the monotonic time (CLOCK_MONOTONIC)
+ * 
+ * Calculates a monotically incrasing time since system boot
+ * that continues to increment when the syste is asleep.
+ * 
+ * Warnings to everyone trying to simplify this:
+ * - Using mach_continuous_time is not equivalent to this, see
+ *   the darwin manpage about CLOCK_MONOTONIC_RAW for an explanation.
+ * - Using mach_absolute_time is not equivalent to this, as it does
+ *   not continue to increment when the system is asleep.
+ * - The boot time is queried twice in a loop and only used if both
+ *   match. This is done to detect if the boot time change since we
+ *   obtained the current time of day, as the boot time can change
+ *   when the system wallclock is adjusted, as that will adjust the
+ *   boot time accordingly.
+ *
+ * \param[out]  tv   Timeval struct to write the monotonic time to
+ *
+ * \return 0 on success, else -1 and errno set
+ */
+static int vlc__get_monotonic(struct timeval *tv)
+{
+    int ret;
+    struct timeval currenttime;
+    struct timeval boottime_begin;
+    struct timeval boottime_end;
+
+    do {
+        ret = vlc__get_system_boottime(&boottime_begin);
+        if (ret != 0)
+            return ret;
+
+        ret = gettimeofday(&currenttime, NULL);
+        if (ret != 0)
+            return ret;
+
+        ret = vlc__get_system_boottime(&boottime_end);
+        if (ret != 0)
+            return ret;
+    } while (timercmp(&boottime_begin, &boottime_end, !=));
+
+    timersub(&currenttime, &boottime_begin, tv);
+    return 0;
+}
+
+int clock_gettime(clockid_t clock_id, struct timespec *tp)
+{
+    int ret = 0;
+    struct timeval tv;
+
+    switch (clock_id) {
+        case CLOCK_MONOTONIC:
+            ret = vlc__get_monotonic(&tv);
+            break;
+        case CLOCK_REALTIME:
+            ret = gettimeofday(&tv, NULL);
+            break;
+        default:
+            errno = EINVAL;
+            return -1;
+    }
+
+    if (ret == 0)
+        TIMEVAL_TO_TIMESPEC(&tv, tp);
+    return ret;
+}
diff --git a/configure.ac b/configure.ac
index bc1874cb97..134cae50a6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -179,6 +179,10 @@ case "${host_os}" in
     VLC_ADD_LIBS([libvlc vlc],[-Wl,-undefined,dynamic_lookup,-framework,AppKit])
     VLC_ADD_LIBS([libvlccore],[-Wl,-framework,CoreFoundation,-framework,CoreServices])
 
+    dnl macOS 10.11 lacks clock_gettime, introduced with 10.12
+    AC_LIBOBJ([clock_gettime])
+    AC_CHECK_FUNCS([clock_gettime])
+
     AC_EGREP_CPP(yes,
             [#import <TargetConditionals.h>
              #if TARGET_OS_IPHONE
diff --git a/include/vlc_fixups.h b/include/vlc_fixups.h
index 8fd01da0ce..055bcf84d6 100644
--- a/include/vlc_fixups.h
+++ b/include/vlc_fixups.h
@@ -658,6 +658,17 @@ FILE *vlc_win32_tmpfile(void);
 
 #ifdef __APPLE__
 # define fdatasync fsync
+
+# include <time.h>
+# ifndef CLOCK_REALTIME
+#  define CLOCK_REALTIME 0
+# endif
+# ifndef CLOCK_MONOTONIC
+#  define CLOCK_MONOTONIC 6
+# endif
+# ifndef HAVE_CLOCK_GETTIME
+int clock_gettime(clockid_t clock_id, struct timespec *tp);
+# endif
 #endif
 
 #ifdef __cplusplus
-- 
2.21.1 (Apple Git-122.3)