Github user wy96f commented on the issue:
https://github.com/apache/activemq-artemis/pull/2481
@michaelandrepearce @franz1981
Here is the code of System::nanoTime from openjdk:
jlong os::javaTimeNanos() {
if (Linux::supports_monotonic_clock()) {
struct timespec tp;
int status = Linux::clock_gettime(CLOCK_MONOTONIC, &tp);
assert(status == 0, "gettime error");
jlong result = jlong(tp.tv_sec) * (1000 * 1000 * 1000) +
jlong(tp.tv_nsec);
return result;
} else {
timeval time;
int status = gettimeofday(&time, NULL);
assert(status != -1, "linux error");
jlong usecs = jlong(time.tv_sec) * (1000 * 1000) + jlong(time.tv_usec);
return 1000 * usecs;
}
}
If monotonic clock is not supported, nanoTime is implemented like
currentTimeMillis.
If clock_gettime is used, as man page says: CLOCK_MONOTONIC_RAW (since
Linux 2.6.28; Linux-specific) similar to CLOCK_MONOTONIC, but provides access
to a raw hardware-based time that is not subject to NTP adjustments. That's to
say CLOCK_MONOTONIC maybe affected by ntp. See
https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8006942,
https://github.com/rust-lang/rust/issues/37902 for reference. Not sure
CLOCK_MONOTONIC won't jump backward, please correct me if anything wrong:)
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