opal/util: add portable wrappers for clock_gettime()/getres()

As of Dec 2021, it turns out that CLOCK_MONOTONIC can actually go
backwards on macOS (!).  Add two simple portable wrappers that use
CLOCK_MONOTONIC_RAW on Darwin (which doesn't go backwards) and
CLOCK_MONOTONIC everywhere else.

Additionally, if the underlying OS does not have clock_gettime(), use
gettimeofday() instead.

Signed-off-by: Jeff Squyres <[email protected]>

Author: jsquyres

opal/util/Makefile.am

@@ -9,7 +9,7 @@
 #                         University of Stuttgart.  All rights reserved.
 # Copyright (c) 2004-2005 The Regents of the University of California.
 #                         All rights reserved.
-# Copyright (c) 2007-2015 Cisco Systems, Inc.  All rights reserved.
+# Copyright (c) 2007-2022 Cisco Systems, Inc.  All rights reserved
 # Copyright (c) 2013      NVIDIA Corporation.  All rights reserved.
 # Copyright (c) 2013      Intel, Inc. All rights reserved
 # Copyright (c) 2016      Los Alamos National Security, LLC. All rights
@@ -48,6 +48,7 @@ headers = \
 	bipartite_graph.h \
 	bipartite_graph_internal.h \
         bit_ops.h \
+        clock_gettime.h \
         cmd_line.h \
         crc.h \
         daemon_init.h \

opal/util/clock_gettime.h

@@ -0,0 +1,104 @@
+/*
+ * Copyright (c) 2022 Cisco Systems, Inc. All rights reserved.
+ * $COPYRIGHT$
+ *
+ * Additional copyrights may follow
+ *
+ * $HEADER$
+ */
+
+/** @file clock_gettime.h
+ *
+ * Simple, portable wrappers around clock_gettime(3) and
+ * clock_getres(3) to always get monotonically-increasing time.
+ *
+ * If the underlying OS does not have clock_gettime(3), use
+ * gettimeofday(3) instead.
+ *
+ * We intentionally do not use the OPAL timer framework for
+ * high-prevision time here; see
+ * https://github.com/open-mpi/ompi/issues/3003 for more details.
+ *
+ * As of Dec 2021, it turns out that CLOCK_MONOTONIC can actually go
+ * backwards on macOS (!).  CLOCK_MONOTONIC does *not* go backwards on
+ * Linux (or anywhere else we can find), though, even in the presence
+ * of small NTP time adjustments -- e.g., adjtime(3) simply slightly
+ * speeds up or slows down the system clock to make it eventually get
+ * to the desired time.  On macOS, we can use CLOCK_MONOTONIC_RAW,
+ * which never goes backwards.
+ *
+ * Hence, for these wrappers, use CLOCK_MONOTONIC_RAW on Darwin, and
+ * use CLOCK_MONOTONIC everywhere else.
+ *
+ * See
+ * https://github.com/open-mpi/ompi/pull/8057#discussion_r762612710
+ * and
+ * https://github.com/open-mpi/ompi/pull/8057#discussion_r762618783
+ * for more details.
+ */
+
+#ifndef OPAL_UTIL_CLOCK_GETTIME_H_
+#define OPAL_UTIL_CLOCK_GETTIME_H_
+
+#include "opal_config.h"
+
+#include <time.h>
+
+#if OPAL_HAVE_CLOCK_GETTIME
+#if defined(__darwin__)
+#define OPAL_CLOCK_TYPE CLOCK_MONOTONIC_RAW
+#else
+#define OPAL_CLOCK_TYPE CLOCK_MONOTONIC
+#endif
+#endif // OPAL_HAVE_CLOCK_GETTIME
+
+
+/**
+ * Simple, portable wrapper around clock_gettime(3) for high-precision time.
+ *
+ * If the underlying system does not have clock_gettime(3), use
+ * gettimeofday(3) instead.
+ *
+ * @param spec (OUT) Struct to return the time
+ * @return Return value from underlying clock_gettime()
+ */
+static inline int opal_clock_gettime(struct timespec *spec)
+{
+#if OPAL_HAVE_CLOCK_GETTIME
+    return clock_gettime(OPAL_CLOCK_TYPE, spec);
+#else
+    // If we do not have clock_gettime(), fall back to gettimeofday()
+    struct timeval tv;
+    int ret = gettimeofday(&tv, NULL);
+
+    spec->tv_sec = tv.tv_sec;
+    // Elevate the micrseconds to nanoseconds
+    spec->tv_nsec = tv.tv_usec * 1000;
+
+    return ret;
+#endif
+}
+
+/**
+ * Simple, portable wrapper around clock_getres(3) for high-precision time.
+ *
+ * If the underlying system does not have clock_gettime(3), return usec
+ * precison (because opal_clock_gettime() will be using gettimeofday(3)).
+ *
+ * @param spec (OUT) Struct to return the resolution
+ * @return Return value from underlying clock_getres()
+ */
+static inline int opal_clock_getres(struct timespec *spec)
+{
+#if OPAL_HAVE_CLOCK_GETTIME
+    return clock_getres(OPAL_CLOCK_TYPE, spec);
+#else
+    // If we don't have clock_gettime(), just return usec precision.
+    spec->tv_sec = 0;
+    spec->tv_sec = 1.0e-6;
+
+    return 0;
+#endif
+}
+
+#endif // OPAL_UTIL_CLOCK_GETTIME_H_