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8242504: Enhance the system clock to nanosecond precision

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Co-authored-by: Mark Kralj-Taylor <kralj.mark@gmail.com>
Reviewed-by: dfuchs, rriggs, dcubed, vtewari
This commit is contained in:
David Holmes 2020-05-28 22:34:02 -04:00
parent 60ac615aa8
commit 7228978b19
6 changed files with 62 additions and 31 deletions
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35
src/hotspot/os/linux/os_linux.cpp
View File

@ -1376,18 +1376,35 @@ double os::elapsedVTime() {
}
jlong os::javaTimeMillis() {
timeval time;
int status = gettimeofday(&time, NULL);
assert(status != -1, "linux error");
return jlong(time.tv_sec) * 1000 + jlong(time.tv_usec / 1000);
if (os::Posix::supports_clock_gettime()) {
struct timespec ts;
int status = os::Posix::clock_gettime(CLOCK_REALTIME, &ts);
assert_status(status == 0, status, "gettime error");
return jlong(ts.tv_sec) * MILLIUNITS +
jlong(ts.tv_nsec) / NANOUNITS_PER_MILLIUNIT;
} else {
timeval time;
int status = gettimeofday(&time, NULL);
assert(status != -1, "linux error");
return jlong(time.tv_sec) * MILLIUNITS +
jlong(time.tv_usec) / (MICROUNITS / MILLIUNITS);
}
}
void os::javaTimeSystemUTC(jlong &seconds, jlong &nanos) {
timeval time;
int status = gettimeofday(&time, NULL);
assert(status != -1, "linux error");
seconds = jlong(time.tv_sec);
nanos = jlong(time.tv_usec) * 1000;
if (os::Posix::supports_clock_gettime()) {
struct timespec ts;
int status = os::Posix::clock_gettime(CLOCK_REALTIME, &ts);
assert_status(status == 0, status, "gettime error");
seconds = jlong(ts.tv_sec);
nanos = jlong(ts.tv_nsec);
} else {
timeval time;
int status = gettimeofday(&time, NULL);
assert(status != -1, "linux error");
seconds = jlong(time.tv_sec);
nanos = jlong(time.tv_usec) * (NANOUNITS / MICROUNITS);
}
}
void os::Linux::fast_thread_clock_init() {

16
src/hotspot/os/posix/os_posix.cpp
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@ -1638,6 +1638,8 @@ void os::Posix::save_preinstalled_handler(int sig, struct sigaction& oldAct) {
int (*os::Posix::_clock_gettime)(clockid_t, struct timespec *) = NULL;
int (*os::Posix::_clock_getres)(clockid_t, struct timespec *) = NULL;
bool os::Posix::_supports_monotonic_clock = false;
static int (*_pthread_condattr_setclock)(pthread_condattr_t *, clockid_t) = NULL;
static bool _use_clock_monotonic_condattr = false;
@ -1653,7 +1655,7 @@ void os::Posix::init(void) {
void* handle = NULL;
// For linux we need librt, for other OS we can find
// For older linux we need librt, for other OS we can find
// this function in regular libc.
#ifdef NEEDS_LIBRT
// We do dlopen's in this particular order due to bug in linux
@ -1673,6 +1675,8 @@ void os::Posix::init(void) {
int (*clock_gettime_func)(clockid_t, struct timespec*) =
(int(*)(clockid_t, struct timespec*))dlsym(handle, "clock_gettime");
if (clock_getres_func != NULL && clock_gettime_func != NULL) {
_clock_gettime = clock_gettime_func;
_clock_getres = clock_getres_func;
// We assume that if both clock_gettime and clock_getres support
// CLOCK_MONOTONIC then the OS provides true high-res monotonic clock.
struct timespec res;
@ -1680,15 +1684,7 @@ void os::Posix::init(void) {
if (clock_getres_func(CLOCK_MONOTONIC, &res) == 0 &&
clock_gettime_func(CLOCK_MONOTONIC, &tp) == 0) {
// Yes, monotonic clock is supported.
_clock_gettime = clock_gettime_func;
_clock_getres = clock_getres_func;
} else {
#ifdef NEEDS_LIBRT
// Close librt if there is no monotonic clock.
if (handle != RTLD_DEFAULT) {
dlclose(handle);
}
#endif
_supports_monotonic_clock = true;
}
}

6
src/hotspot/os/posix/os_posix.hpp
View File

@ -128,18 +128,18 @@ public:
#ifdef SUPPORTS_CLOCK_MONOTONIC
private:
static bool _supports_monotonic_clock;
// These need to be members so we can access them from inline functions
static int (*_clock_gettime)(clockid_t, struct timespec *);
static int (*_clock_getres)(clockid_t, struct timespec *);
public:
static bool supports_monotonic_clock();
static bool supports_clock_gettime();
static int clock_gettime(clockid_t clock_id, struct timespec *tp);
static int clock_getres(clockid_t clock_id, struct timespec *tp);
#else
static bool supports_monotonic_clock() { return false; }
static bool supports_clock_gettime() { return false; }
#endif
static void to_RTC_abstime(timespec* abstime, int64_t millis);

4
src/hotspot/os/posix/os_posix.inline.hpp
View File

@ -32,6 +32,10 @@
// Exported clock functionality
inline bool os::Posix::supports_monotonic_clock() {
return _supports_monotonic_clock;
}
inline bool os::Posix::supports_clock_gettime() {
return _clock_gettime != NULL;
}

22
test/jdk/java/time/test/java/time/TestClock_System.java
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2012, 2016, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2012, 2020, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -177,7 +177,8 @@ public class TestClock_System {
+ formatTime("\n\thighest1", highest1));
}
int count=0;
int countBetterThanMillisPrecision = 0;
int countBetterThanMicrosPrecision = 0;
// let's preheat the system a bit:
int lastNanos = 0;
for (int i = 0; i < 1000 ; i++) {
@ -191,7 +192,10 @@ public class TestClock_System {
lastNanos = nanos;
if ((nanos % 1000000) > 0) {
count++; // we have micro seconds
countBetterThanMillisPrecision++; // we have microseconds
}
if ((nanos % 1000) > 0) {
countBetterThanMicrosPrecision++; // we have nanoseconds
}
if ((sysnan % 1000000) > 0) {
throw new RuntimeException("Expected only millisecconds "
@ -200,13 +204,17 @@ public class TestClock_System {
}
}
System.out.println("\nNumber of time stamps which had better than"
+ " millisecond precision: "+count+"/"+1000);
+ " millisecond precision: "
+ countBetterThanMillisPrecision + "/" + 1000);
System.out.println("\nNumber of time stamps which had better than"
+ " microsecond precision: "
+ countBetterThanMicrosPrecision + "/" + 1000);
System.out.println(formatTime("\nsystemUTC ", system1));
System.out.println(formatTime("highestResolutionUTC ", highest1));
if (count == 0) {
if (countBetterThanMillisPrecision == 0) {
System.err.println("Something is strange: no microsecond "
+ "precision with highestResolutionUTC?");
throw new RuntimeException("Micro second preccision not reached");
+ "precision with highestResolutionUTC?");
throw new RuntimeException("Micro second precision not reached");
}
// check again

10
test/micro/org/openjdk/bench/java/lang/Systems.java → test/micro/org/openjdk/bench/java/lang/SystemTime.java
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2014, 2020, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -27,11 +27,12 @@ import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import java.time.Instant;
import java.util.concurrent.TimeUnit;
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class Systems {
public class SystemTime {
@Benchmark
public long currentTimeMillis() {
@ -43,4 +44,9 @@ public class Systems {
return System.nanoTime();
}
@Benchmark
public long instantNowAsEpochNanos() {
Instant now = Instant.now();
return now.getEpochSecond() * 1_000_000_000L + now.getNano();
}
}