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-rw-r--r--libnetdata/clocks/Makefile.am8
-rw-r--r--libnetdata/clocks/README.md10
-rw-r--r--libnetdata/clocks/clocks.c478
-rw-r--r--libnetdata/clocks/clocks.h162
4 files changed, 658 insertions, 0 deletions
diff --git a/libnetdata/clocks/Makefile.am b/libnetdata/clocks/Makefile.am
new file mode 100644
index 00000000..161784b8
--- /dev/null
+++ b/libnetdata/clocks/Makefile.am
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+AUTOMAKE_OPTIONS = subdir-objects
+MAINTAINERCLEANFILES = $(srcdir)/Makefile.in
+
+dist_noinst_DATA = \
+ README.md \
+ $(NULL)
diff --git a/libnetdata/clocks/README.md b/libnetdata/clocks/README.md
new file mode 100644
index 00000000..33b0f0e8
--- /dev/null
+++ b/libnetdata/clocks/README.md
@@ -0,0 +1,10 @@
+<!--
+custom_edit_url: "https://github.com/netdata/netdata/edit/master/libnetdata/clocks/README.md"
+title: "Clocks"
+sidebar_label: "Clocks"
+learn_status: "Published"
+learn_topic_type: "References"
+learn_rel_path: "Developers/libnetdata"
+-->
+
+# Clocks \ No newline at end of file
diff --git a/libnetdata/clocks/clocks.c b/libnetdata/clocks/clocks.c
new file mode 100644
index 00000000..adbad045
--- /dev/null
+++ b/libnetdata/clocks/clocks.c
@@ -0,0 +1,478 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "../libnetdata.h"
+
+// defaults are for compatibility
+// call clocks_init() once, to optimize these default settings
+static clockid_t clock_boottime_to_use = CLOCK_MONOTONIC;
+static clockid_t clock_monotonic_to_use = CLOCK_MONOTONIC;
+
+// the default clock resolution is 1ms
+#define DEFAULT_CLOCK_RESOLUTION_UT ((usec_t)0 * USEC_PER_SEC + (usec_t)1 * USEC_PER_MS)
+
+// the max clock resolution is 10ms
+#define MAX_CLOCK_RESOLUTION_UT ((usec_t)0 * USEC_PER_SEC + (usec_t)10 * USEC_PER_MS)
+
+usec_t clock_monotonic_resolution = DEFAULT_CLOCK_RESOLUTION_UT;
+usec_t clock_realtime_resolution = DEFAULT_CLOCK_RESOLUTION_UT;
+
+#ifndef HAVE_CLOCK_GETTIME
+inline int clock_gettime(clockid_t clk_id __maybe_unused, struct timespec *ts) {
+ struct timeval tv;
+ if(unlikely(gettimeofday(&tv, NULL) == -1)) {
+ netdata_log_error("gettimeofday() failed.");
+ return -1;
+ }
+ ts->tv_sec = tv.tv_sec;
+ ts->tv_nsec = (long)((tv.tv_usec % USEC_PER_SEC) * NSEC_PER_USEC);
+ return 0;
+}
+#endif
+
+// Similar to CLOCK_MONOTONIC, but provides access to a raw hardware-based time that is not subject to NTP adjustments
+// or the incremental adjustments performed by adjtime(3). This clock does not count time that the system is suspended
+
+static void test_clock_monotonic_raw(void) {
+#ifdef CLOCK_MONOTONIC_RAW
+ struct timespec ts;
+ if(clock_gettime(CLOCK_MONOTONIC_RAW, &ts) == -1 && errno == EINVAL)
+ clock_monotonic_to_use = CLOCK_MONOTONIC;
+ else
+ clock_monotonic_to_use = CLOCK_MONOTONIC_RAW;
+#else
+ clock_monotonic_to_use = CLOCK_MONOTONIC;
+#endif
+}
+
+// When running a binary with CLOCK_BOOTTIME defined on a system with a linux kernel older than Linux 2.6.39 the
+// clock_gettime(2) system call fails with EINVAL. In that case it must fall-back to CLOCK_MONOTONIC.
+
+static void test_clock_boottime(void) {
+ struct timespec ts;
+ if(clock_gettime(CLOCK_BOOTTIME, &ts) == -1 && errno == EINVAL)
+ clock_boottime_to_use = clock_monotonic_to_use;
+ else
+ clock_boottime_to_use = CLOCK_BOOTTIME;
+}
+
+static usec_t get_clock_resolution(clockid_t clock) {
+ struct timespec ts = { 0 };
+
+ if(clock_getres(clock, &ts) == 0) {
+ usec_t ret = (usec_t)ts.tv_sec * USEC_PER_SEC + (usec_t)ts.tv_nsec / NSEC_PER_USEC;
+ if(!ret && ts.tv_nsec > 0 && ts.tv_nsec < NSEC_PER_USEC)
+ return (usec_t)1;
+
+ else if(ret > MAX_CLOCK_RESOLUTION_UT) {
+ nd_log(NDLS_DAEMON, NDLP_ERR, "clock_getres(%d) returned %"PRIu64" usec is out of range, using defaults for clock resolution.", (int)clock, ret);
+ return DEFAULT_CLOCK_RESOLUTION_UT;
+ }
+
+ return ret;
+ }
+ else {
+ nd_log(NDLS_DAEMON, NDLP_ERR, "clock_getres(%d) failed, using defaults for clock resolution.", (int)clock);
+ return DEFAULT_CLOCK_RESOLUTION_UT;
+ }
+}
+
+// perform any initializations required for clocks
+
+void clocks_init(void) {
+ // monotonic raw has to be tested before boottime
+ test_clock_monotonic_raw();
+
+ // boottime has to be tested after monotonic coarse
+ test_clock_boottime();
+
+ clock_monotonic_resolution = get_clock_resolution(clock_monotonic_to_use);
+ clock_realtime_resolution = get_clock_resolution(CLOCK_REALTIME);
+}
+
+inline time_t now_sec(clockid_t clk_id) {
+ struct timespec ts;
+ if(unlikely(clock_gettime(clk_id, &ts) == -1)) {
+ netdata_log_error("clock_gettime(%d, &timespec) failed.", clk_id);
+ return 0;
+ }
+ return ts.tv_sec;
+}
+
+inline usec_t now_usec(clockid_t clk_id) {
+ struct timespec ts;
+ if(unlikely(clock_gettime(clk_id, &ts) == -1)) {
+ netdata_log_error("clock_gettime(%d, &timespec) failed.", clk_id);
+ return 0;
+ }
+ return (usec_t)ts.tv_sec * USEC_PER_SEC + (usec_t)(ts.tv_nsec % NSEC_PER_SEC) / NSEC_PER_USEC;
+}
+
+inline int now_timeval(clockid_t clk_id, struct timeval *tv) {
+ struct timespec ts;
+
+ if(unlikely(clock_gettime(clk_id, &ts) == -1)) {
+ netdata_log_error("clock_gettime(%d, &timespec) failed.", clk_id);
+ tv->tv_sec = 0;
+ tv->tv_usec = 0;
+ return -1;
+ }
+
+ tv->tv_sec = ts.tv_sec;
+ tv->tv_usec = (suseconds_t)((ts.tv_nsec % NSEC_PER_SEC) / NSEC_PER_USEC);
+ return 0;
+}
+
+inline time_t now_realtime_sec(void) {
+ return now_sec(CLOCK_REALTIME);
+}
+
+inline msec_t now_realtime_msec(void) {
+ return now_usec(CLOCK_REALTIME) / USEC_PER_MS;
+}
+
+inline usec_t now_realtime_usec(void) {
+ return now_usec(CLOCK_REALTIME);
+}
+
+inline int now_realtime_timeval(struct timeval *tv) {
+ return now_timeval(CLOCK_REALTIME, tv);
+}
+
+inline time_t now_monotonic_sec(void) {
+ return now_sec(clock_monotonic_to_use);
+}
+
+inline usec_t now_monotonic_usec(void) {
+ return now_usec(clock_monotonic_to_use);
+}
+
+inline int now_monotonic_timeval(struct timeval *tv) {
+ return now_timeval(clock_monotonic_to_use, tv);
+}
+
+inline time_t now_monotonic_high_precision_sec(void) {
+ return now_sec(CLOCK_MONOTONIC);
+}
+
+inline usec_t now_monotonic_high_precision_usec(void) {
+ return now_usec(CLOCK_MONOTONIC);
+}
+
+inline int now_monotonic_high_precision_timeval(struct timeval *tv) {
+ return now_timeval(CLOCK_MONOTONIC, tv);
+}
+
+inline time_t now_boottime_sec(void) {
+ return now_sec(clock_boottime_to_use);
+}
+
+inline usec_t now_boottime_usec(void) {
+ return now_usec(clock_boottime_to_use);
+}
+
+inline int now_boottime_timeval(struct timeval *tv) {
+ return now_timeval(clock_boottime_to_use, tv);
+}
+
+inline usec_t timeval_usec(struct timeval *tv) {
+ return (usec_t)tv->tv_sec * USEC_PER_SEC + (tv->tv_usec % USEC_PER_SEC);
+}
+
+inline msec_t timeval_msec(struct timeval *tv) {
+ return (msec_t)tv->tv_sec * MSEC_PER_SEC + ((tv->tv_usec % USEC_PER_SEC) / MSEC_PER_SEC);
+}
+
+inline susec_t dt_usec_signed(struct timeval *now, struct timeval *old) {
+ usec_t ts1 = timeval_usec(now);
+ usec_t ts2 = timeval_usec(old);
+
+ if(likely(ts1 >= ts2)) return (susec_t)(ts1 - ts2);
+ return -((susec_t)(ts2 - ts1));
+}
+
+inline usec_t dt_usec(struct timeval *now, struct timeval *old) {
+ usec_t ts1 = timeval_usec(now);
+ usec_t ts2 = timeval_usec(old);
+ return (ts1 > ts2) ? (ts1 - ts2) : (ts2 - ts1);
+}
+
+#ifdef __linux__
+void sleep_to_absolute_time(usec_t usec) {
+ static int einval_printed = 0, enotsup_printed = 0, eunknown_printed = 0;
+ clockid_t clock = CLOCK_REALTIME;
+
+ struct timespec req = {
+ .tv_sec = (time_t)(usec / USEC_PER_SEC),
+ .tv_nsec = (suseconds_t)((usec % USEC_PER_SEC) * NSEC_PER_USEC)
+ };
+
+ errno = 0;
+ int ret = 0;
+ while( (ret = clock_nanosleep(clock, TIMER_ABSTIME, &req, NULL)) != 0 ) {
+ if(ret == EINTR) {
+ errno = 0;
+ continue;
+ }
+ else {
+ if (ret == EINVAL) {
+ if (!einval_printed) {
+ einval_printed++;
+ netdata_log_error("Invalid time given to clock_nanosleep(): clockid = %d, tv_sec = %lld, tv_nsec = %ld",
+ clock,
+ (long long)req.tv_sec,
+ req.tv_nsec);
+ }
+ } else if (ret == ENOTSUP) {
+ if (!enotsup_printed) {
+ enotsup_printed++;
+ netdata_log_error("Invalid clock id given to clock_nanosleep(): clockid = %d, tv_sec = %lld, tv_nsec = %ld",
+ clock,
+ (long long)req.tv_sec,
+ req.tv_nsec);
+ }
+ } else {
+ if (!eunknown_printed) {
+ eunknown_printed++;
+ netdata_log_error("Unknown return value %d from clock_nanosleep(): clockid = %d, tv_sec = %lld, tv_nsec = %ld",
+ ret,
+ clock,
+ (long long)req.tv_sec,
+ req.tv_nsec);
+ }
+ }
+ sleep_usec(usec);
+ }
+ }
+};
+#endif
+
+#define HEARTBEAT_ALIGNMENT_STATISTICS_SIZE 10
+netdata_mutex_t heartbeat_alignment_mutex = NETDATA_MUTEX_INITIALIZER;
+static size_t heartbeat_alignment_id = 0;
+
+struct heartbeat_thread_statistics {
+ size_t sequence;
+ usec_t dt;
+};
+static struct heartbeat_thread_statistics heartbeat_alignment_values[HEARTBEAT_ALIGNMENT_STATISTICS_SIZE] = { 0 };
+
+void heartbeat_statistics(usec_t *min_ptr, usec_t *max_ptr, usec_t *average_ptr, size_t *count_ptr) {
+ struct heartbeat_thread_statistics current[HEARTBEAT_ALIGNMENT_STATISTICS_SIZE];
+ static struct heartbeat_thread_statistics old[HEARTBEAT_ALIGNMENT_STATISTICS_SIZE] = { 0 };
+
+ memcpy(current, heartbeat_alignment_values, sizeof(struct heartbeat_thread_statistics) * HEARTBEAT_ALIGNMENT_STATISTICS_SIZE);
+
+ usec_t min = 0, max = 0, total = 0, average = 0;
+ size_t i, count = 0;
+ for(i = 0; i < HEARTBEAT_ALIGNMENT_STATISTICS_SIZE ;i++) {
+ if(current[i].sequence == old[i].sequence) continue;
+ usec_t value = current[i].dt - old[i].dt;
+
+ if(!count) {
+ min = max = total = value;
+ count = 1;
+ }
+ else {
+ total += value;
+ if(value < min) min = value;
+ if(value > max) max = value;
+ count++;
+ }
+ }
+ if(count)
+ average = total / count;
+
+ if(min_ptr) *min_ptr = min;
+ if(max_ptr) *max_ptr = max;
+ if(average_ptr) *average_ptr = average;
+ if(count_ptr) *count_ptr = count;
+
+ memcpy(old, current, sizeof(struct heartbeat_thread_statistics) * HEARTBEAT_ALIGNMENT_STATISTICS_SIZE);
+}
+
+inline void heartbeat_init(heartbeat_t *hb) {
+ hb->realtime = 0ULL;
+ hb->randomness = (usec_t)250 * USEC_PER_MS + ((usec_t)(now_realtime_usec() * clock_realtime_resolution) % (250 * USEC_PER_MS));
+ hb->randomness -= (hb->randomness % clock_realtime_resolution);
+
+ netdata_mutex_lock(&heartbeat_alignment_mutex);
+ hb->statistics_id = heartbeat_alignment_id;
+ heartbeat_alignment_id++;
+ netdata_mutex_unlock(&heartbeat_alignment_mutex);
+
+ if(hb->statistics_id < HEARTBEAT_ALIGNMENT_STATISTICS_SIZE) {
+ heartbeat_alignment_values[hb->statistics_id].dt = 0;
+ heartbeat_alignment_values[hb->statistics_id].sequence = 0;
+ }
+}
+
+// waits for the next heartbeat
+// it waits using the monotonic clock
+// it returns the dt using the realtime clock
+
+usec_t heartbeat_next(heartbeat_t *hb, usec_t tick) {
+ if(unlikely(hb->randomness > tick / 2)) {
+ // TODO: The heartbeat tick should be specified at the heartbeat_init() function
+ usec_t tmp = (now_realtime_usec() * clock_realtime_resolution) % (tick / 2);
+
+ nd_log_limit_static_global_var(erl, 10, 0);
+ nd_log_limit(&erl, NDLS_DAEMON, NDLP_NOTICE,
+ "heartbeat randomness of %"PRIu64" is too big for a tick of %"PRIu64" - setting it to %"PRIu64"",
+ hb->randomness, tick, tmp);
+ hb->randomness = tmp;
+ }
+
+ usec_t dt;
+ usec_t now = now_realtime_usec();
+ usec_t next = now - (now % tick) + tick + hb->randomness;
+
+ // align the next time we want to the clock resolution
+ if(next % clock_realtime_resolution)
+ next = next - (next % clock_realtime_resolution) + clock_realtime_resolution;
+
+ // sleep_usec() has a loop to guarantee we will sleep for at least the requested time.
+ // According the specs, when we sleep for a relative time, clock adjustments should not affect the duration
+ // we sleep.
+ sleep_usec_with_now(next - now, now);
+ now = now_realtime_usec();
+ dt = now - hb->realtime;
+
+ if(hb->statistics_id < HEARTBEAT_ALIGNMENT_STATISTICS_SIZE) {
+ heartbeat_alignment_values[hb->statistics_id].dt += now - next;
+ heartbeat_alignment_values[hb->statistics_id].sequence++;
+ }
+
+ if(unlikely(now < next)) {
+ errno = 0;
+ nd_log_limit_static_global_var(erl, 10, 0);
+ nd_log_limit(&erl, NDLS_DAEMON, NDLP_NOTICE,
+ "heartbeat clock: woke up %"PRIu64" microseconds earlier than expected "
+ "(can be due to the CLOCK_REALTIME set to the past).",
+ next - now);
+ }
+ else if(unlikely(now - next > tick / 2)) {
+ errno = 0;
+ nd_log_limit_static_global_var(erl, 10, 0);
+ nd_log_limit(&erl, NDLS_DAEMON, NDLP_NOTICE,
+ "heartbeat clock: woke up %"PRIu64" microseconds later than expected "
+ "(can be due to system load or the CLOCK_REALTIME set to the future).",
+ now - next);
+ }
+
+ if(unlikely(!hb->realtime)) {
+ // the first time return zero
+ dt = 0;
+ }
+
+ hb->realtime = now;
+ return dt;
+}
+
+void sleep_usec_with_now(usec_t usec, usec_t started_ut) {
+ // we expect microseconds (1.000.000 per second)
+ // but timespec is nanoseconds (1.000.000.000 per second)
+ struct timespec rem = { 0, 0 }, req = {
+ .tv_sec = (time_t) (usec / USEC_PER_SEC),
+ .tv_nsec = (suseconds_t) ((usec % USEC_PER_SEC) * NSEC_PER_USEC)
+ };
+
+ // make sure errno is not EINTR
+ errno = 0;
+
+ if(!started_ut)
+ started_ut = now_realtime_usec();
+
+ usec_t end_ut = started_ut + usec;
+
+ while (nanosleep(&req, &rem) != 0) {
+ if (likely(errno == EINTR && (rem.tv_sec || rem.tv_nsec))) {
+ req = rem;
+ rem = (struct timespec){ 0, 0 };
+
+ // break an infinite loop
+ errno = 0;
+
+ usec_t now_ut = now_realtime_usec();
+ if(now_ut >= end_ut)
+ break;
+
+ usec_t remaining_ut = (usec_t)req.tv_sec * USEC_PER_SEC + (usec_t)req.tv_nsec * NSEC_PER_USEC > usec;
+ usec_t check_ut = now_ut - started_ut;
+ if(remaining_ut > check_ut) {
+ req = (struct timespec){
+ .tv_sec = (time_t) ( check_ut / USEC_PER_SEC),
+ .tv_nsec = (suseconds_t) ((check_ut % USEC_PER_SEC) * NSEC_PER_USEC)
+ };
+ }
+ }
+ else {
+ netdata_log_error("Cannot nanosleep() for %"PRIu64" microseconds.", usec);
+ break;
+ }
+ }
+}
+
+static inline collected_number uptime_from_boottime(void) {
+#ifdef CLOCK_BOOTTIME_IS_AVAILABLE
+ return (collected_number)(now_boottime_usec() / USEC_PER_MS);
+#else
+ netdata_log_error("uptime cannot be read from CLOCK_BOOTTIME on this system.");
+ return 0;
+#endif
+}
+
+static procfile *read_proc_uptime_ff = NULL;
+static inline collected_number read_proc_uptime(char *filename) {
+ if(unlikely(!read_proc_uptime_ff)) {
+ read_proc_uptime_ff = procfile_open(filename, " \t", PROCFILE_FLAG_DEFAULT);
+ if(unlikely(!read_proc_uptime_ff)) return 0;
+ }
+
+ read_proc_uptime_ff = procfile_readall(read_proc_uptime_ff);
+ if(unlikely(!read_proc_uptime_ff)) return 0;
+
+ if(unlikely(procfile_lines(read_proc_uptime_ff) < 1)) {
+ netdata_log_error("/proc/uptime has no lines.");
+ return 0;
+ }
+ if(unlikely(procfile_linewords(read_proc_uptime_ff, 0) < 1)) {
+ netdata_log_error("/proc/uptime has less than 1 word in it.");
+ return 0;
+ }
+
+ return (collected_number)(strtondd(procfile_lineword(read_proc_uptime_ff, 0, 0), NULL) * 1000.0);
+}
+
+inline collected_number uptime_msec(char *filename){
+ static int use_boottime = -1;
+
+ if(unlikely(use_boottime == -1)) {
+ collected_number uptime_boottime = uptime_from_boottime();
+ collected_number uptime_proc = read_proc_uptime(filename);
+
+ long long delta = (long long)uptime_boottime - (long long)uptime_proc;
+ if(delta < 0) delta = -delta;
+
+ if(delta <= 1000 && uptime_boottime != 0) {
+ procfile_close(read_proc_uptime_ff);
+ netdata_log_info("Using now_boottime_usec() for uptime (dt is %lld ms)", delta);
+ use_boottime = 1;
+ }
+ else if(uptime_proc != 0) {
+ netdata_log_info("Using /proc/uptime for uptime (dt is %lld ms)", delta);
+ use_boottime = 0;
+ }
+ else {
+ netdata_log_error("Cannot find any way to read uptime on this system.");
+ return 1;
+ }
+ }
+
+ collected_number uptime;
+ if(use_boottime)
+ uptime = uptime_from_boottime();
+ else
+ uptime = read_proc_uptime(filename);
+
+ return uptime;
+}
diff --git a/libnetdata/clocks/clocks.h b/libnetdata/clocks/clocks.h
new file mode 100644
index 00000000..2beb14ed
--- /dev/null
+++ b/libnetdata/clocks/clocks.h
@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef NETDATA_CLOCKS_H
+#define NETDATA_CLOCKS_H 1
+
+#include "../libnetdata.h"
+
+#ifndef HAVE_STRUCT_TIMESPEC
+struct timespec {
+ time_t tv_sec; /* seconds */
+ long tv_nsec; /* nanoseconds */
+};
+#endif
+
+#ifndef HAVE_CLOCKID_T
+typedef int clockid_t;
+#endif
+
+typedef uint64_t nsec_t;
+typedef uint64_t msec_t;
+typedef uint64_t usec_t;
+typedef int64_t susec_t;
+
+typedef struct heartbeat {
+ usec_t realtime;
+ usec_t randomness;
+ size_t statistics_id;
+} heartbeat_t;
+
+/* Linux value is as good as any other */
+#ifndef CLOCK_REALTIME
+#define CLOCK_REALTIME 0
+#endif
+
+#ifndef CLOCK_MONOTONIC
+/* fallback to CLOCK_REALTIME if not available */
+#define CLOCK_MONOTONIC CLOCK_REALTIME
+#endif
+
+#ifndef CLOCK_BOOTTIME
+
+#ifdef CLOCK_UPTIME
+/* CLOCK_BOOTTIME falls back to CLOCK_UPTIME on FreeBSD */
+#define CLOCK_BOOTTIME CLOCK_UPTIME
+#else // CLOCK_UPTIME
+/* CLOCK_BOOTTIME falls back to CLOCK_REALTIME */
+#define CLOCK_BOOTTIME CLOCK_REALTIME
+#endif // CLOCK_UPTIME
+
+#else // CLOCK_BOOTTIME
+
+#ifdef HAVE_CLOCK_GETTIME
+#define CLOCK_BOOTTIME_IS_AVAILABLE 1 // required for /proc/uptime
+#endif // HAVE_CLOCK_GETTIME
+
+#endif // CLOCK_BOOTTIME
+
+#ifndef NSEC_PER_MSEC
+#define NSEC_PER_MSEC 1000000ULL
+#endif
+
+#ifndef NSEC_PER_SEC
+#define NSEC_PER_SEC 1000000000ULL
+#endif
+#ifndef NSEC_PER_USEC
+#define NSEC_PER_USEC 1000ULL
+#endif
+
+#ifndef USEC_PER_SEC
+#define USEC_PER_SEC 1000000ULL
+#endif
+#ifndef MSEC_PER_SEC
+#define MSEC_PER_SEC 1000ULL
+#endif
+
+#define USEC_PER_MS 1000ULL
+
+#ifndef HAVE_CLOCK_GETTIME
+/* Fallback function for POSIX.1-2001 clock_gettime() function.
+ *
+ * We use a realtime clock from gettimeofday(), this will
+ * make systems without clock_gettime() support sensitive
+ * to time jumps or hibernation/suspend side effects.
+ */
+int clock_gettime(clockid_t clk_id, struct timespec *ts);
+#endif
+
+/*
+ * Three clocks are available (cf. man 3 clock_gettime):
+ *
+ * REALTIME clock (i.e. wall-clock):
+ * This clock is affected by discontinuous jumps in the system time
+ * (e.g., if the system administrator manually changes the clock), and by the incremental adjustments performed by adjtime(3) and NTP.
+ *
+ * MONOTONIC clock
+ * Clock that cannot be set and represents monotonic time since some unspecified starting point.
+ * This clock is not affected by discontinuous jumps in the system time
+ * (e.g., if the system administrator manually changes the clock), but is affected by the incremental adjustments performed by adjtime(3) and NTP.
+ * If not available on the system, this clock falls back to REALTIME clock.
+ *
+ * BOOTTIME clock
+ * Identical to CLOCK_MONOTONIC, except it also includes any time that the system is suspended.
+ * This allows applications to get a suspend-aware monotonic clock without having to deal with the complications of CLOCK_REALTIME,
+ * which may have discontinuities if the time is changed using settimeofday(2).
+ * If not available on the system, this clock falls back to MONOTONIC clock.
+ *
+ * All now_*_timeval() functions fill the `struct timeval` with the time from the appropriate clock.
+ * Those functions return 0 on success, -1 else with errno set appropriately.
+ *
+ * All now_*_sec() functions return the time in seconds from the appropriate clock, or 0 on error.
+ * All now_*_usec() functions return the time in microseconds from the appropriate clock, or 0 on error.
+ *
+ */
+int now_realtime_timeval(struct timeval *tv);
+time_t now_realtime_sec(void);
+usec_t now_realtime_usec(void);
+
+int now_monotonic_timeval(struct timeval *tv);
+time_t now_monotonic_sec(void);
+msec_t now_realtime_msec(void);
+usec_t now_monotonic_usec(void);
+int now_monotonic_high_precision_timeval(struct timeval *tv);
+time_t now_monotonic_high_precision_sec(void);
+usec_t now_monotonic_high_precision_usec(void);
+
+int now_boottime_timeval(struct timeval *tv);
+time_t now_boottime_sec(void);
+usec_t now_boottime_usec(void);
+
+usec_t timeval_usec(struct timeval *tv);
+msec_t timeval_msec(struct timeval *tv);
+
+usec_t dt_usec(struct timeval *now, struct timeval *old);
+susec_t dt_usec_signed(struct timeval *now, struct timeval *old);
+
+void heartbeat_init(heartbeat_t *hb);
+
+/* Sleeps until next multiple of tick using monotonic clock.
+ * Returns elapsed time in microseconds since previous heartbeat
+ */
+usec_t heartbeat_next(heartbeat_t *hb, usec_t tick);
+
+void heartbeat_statistics(usec_t *min_ptr, usec_t *max_ptr, usec_t *average_ptr, size_t *count_ptr);
+
+void sleep_usec_with_now(usec_t usec, usec_t started_ut);
+#define sleep_usec(usec) sleep_usec_with_now(usec, 0);
+
+void clocks_init(void);
+
+// lower level functions - avoid using directly
+time_t now_sec(clockid_t clk_id);
+usec_t now_usec(clockid_t clk_id);
+int now_timeval(clockid_t clk_id, struct timeval *tv);
+
+collected_number uptime_msec(char *filename);
+
+extern usec_t clock_monotonic_resolution;
+extern usec_t clock_realtime_resolution;
+
+void sleep_to_absolute_time(usec_t usec);
+
+#endif /* NETDATA_CLOCKS_H */
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