Java System.nanoTime vs System.currentTimeMillis
根据其文档,System.nanoTime返回 纳秒,因为某个固定但任意的起始时间。然而,在所有x64机器上,我尝试了下面的代码,有时间跳跃,移动固定原点时间。我使用另一种方法(此处为currentTimeMillis)获取正确时间的方法可能存在一些缺陷。然而,测量相对时间(持续时间)的主要目的也受到负面影响 在将不同的队列与LMAX的Disruptor进行比较时,我遇到了这个问题,有时我会得到非常负的延迟。在这些情况下,开始和结束时间戳由不同的线程创建,但延迟是在这些线程完成后计算的 我在这里的代码使用nanoTime花费时间,以currentTimeMillis时间计算固定原点,并在调用之间比较该原点。既然我必须在这里问一个问题:这个代码怎么了?为什么它观察到违反固定原产地合同的情况?还是没有Java System.nanoTime vs System.currentTimeMillis,java,multithreading,nanotime,Java,Multithreading,Nanotime,根据其文档,System.nanoTime返回 纳秒,因为某个固定但任意的起始时间。然而,在所有x64机器上,我尝试了下面的代码,有时间跳跃,移动固定原点时间。我使用另一种方法(此处为currentTimeMillis)获取正确时间的方法可能存在一些缺陷。然而,测量相对时间(持续时间)的主要目的也受到负面影响 在将不同的队列与LMAX的Disruptor进行比较时,我遇到了这个问题,有时我会得到非常负的延迟。在这些情况下,开始和结束时间戳由不同的线程创建,但延迟是在这些线程完成后计算的 我在这里
import java.text.*;
/**
* test coherency between {@link System#currentTimeMillis()} and {@link System#nanoTime()}
*/
public class TimeCoherencyTest {
static final int MAX_THREADS = Math.max( 1, Runtime.getRuntime().availableProcessors() - 1);
static final long RUNTIME_NS = 1000000000L * 100;
static final long BIG_OFFSET_MS = 2;
static long startNanos;
static long firstNanoOrigin;
static {
initNanos();
}
private static void initNanos() {
long millisBefore = System.currentTimeMillis();
long millisAfter;
do {
startNanos = System.nanoTime();
millisAfter = System.currentTimeMillis();
} while ( millisAfter != millisBefore);
firstNanoOrigin = ( long) ( millisAfter - ( startNanos / 1e6));
}
static NumberFormat lnf = DecimalFormat.getNumberInstance();
static {
lnf.setMaximumFractionDigits( 3);
lnf.setGroupingUsed( true);
};
static class TimeCoherency {
long firstOrigin;
long lastOrigin;
long numMismatchToLast = 0;
long numMismatchToFirst = 0;
long numMismatchToFirstBig = 0;
long numChecks = 0;
public TimeCoherency( long firstNanoOrigin) {
firstOrigin = firstNanoOrigin;
lastOrigin = firstOrigin;
}
}
public static void main( String[] args) {
Thread[] threads = new Thread[ MAX_THREADS];
for ( int i = 0; i < MAX_THREADS; i++) {
final int fi = i;
final TimeCoherency tc = new TimeCoherency( firstNanoOrigin);
threads[ i] = new Thread() {
@Override
public void run() {
long start = getNow( tc);
long firstOrigin = tc.lastOrigin; // get the first origin for this thread
System.out.println( "Thread " + fi + " started at " + lnf.format( start) + " ns");
long nruns = 0;
while ( getNow( tc) < RUNTIME_NS) {
nruns++;
}
final long runTimeNS = getNow( tc) - start;
final long originDrift = tc.lastOrigin - firstOrigin;
nruns += 3; // account for start and end call and the one that ends the loop
final long skipped = nruns - tc.numChecks;
System.out.println( "Thread " + fi + " finished after " + lnf.format( nruns) + " runs in " + lnf.format( runTimeNS) + " ns (" + lnf.format( ( double) runTimeNS / nruns) + " ns/call) with"
+ "\n\t" + lnf.format( tc.numMismatchToFirst) + " different from first origin (" + lnf.format( 100.0 * tc.numMismatchToFirst / nruns) + "%)"
+ "\n\t" + lnf.format( tc.numMismatchToLast) + " jumps from last origin (" + lnf.format( 100.0 * tc.numMismatchToLast / nruns) + "%)"
+ "\n\t" + lnf.format( tc.numMismatchToFirstBig) + " different from first origin by more than " + BIG_OFFSET_MS + " ms"
+ " (" + lnf.format( 100.0 * tc.numMismatchToFirstBig / nruns) + "%)"
+ "\n\t" + "total drift: " + lnf.format( originDrift) + " ms, " + lnf.format( skipped) + " skipped (" + lnf.format( 100.0 * skipped / nruns) + " %)");
}};
threads[ i].start();
}
try {
for ( Thread thread : threads) {
thread.join();
}
} catch ( InterruptedException ie) {};
}
public static long getNow( TimeCoherency coherency) {
long millisBefore = System.currentTimeMillis();
long now = System.nanoTime();
if ( coherency != null) {
checkOffset( now, millisBefore, coherency);
}
return now - startNanos;
}
private static void checkOffset( long nanoTime, long millisBefore, TimeCoherency tc) {
long millisAfter = System.currentTimeMillis();
if ( millisBefore != millisAfter) {
// disregard since thread may have slept between calls
return;
}
tc.numChecks++;
long nanoMillis = ( long) ( nanoTime / 1e6);
long nanoOrigin = millisAfter - nanoMillis;
long oldOrigin = tc.lastOrigin;
if ( oldOrigin != nanoOrigin) {
tc.lastOrigin = nanoOrigin;
tc.numMismatchToLast++;
}
if ( tc.firstOrigin != nanoOrigin) {
tc.numMismatchToFirst++;
}
if ( Math.abs( tc.firstOrigin - nanoOrigin) > BIG_OFFSET_MS) {
tc.numMismatchToFirstBig ++;
}
}
}
import java.text.*;
/**
*测试{@link System#currentTimeMillis()}和{@link System#nanoTime()}之间的一致性
*/
公共类时间一致性测试{
静态最终int MAX_THREADS=Math.MAX(1,Runtime.getRuntime().availableProcessors()-1);
静态最终长期运行时间=1000000000L*100;
静态最终长大偏移量=2;
静态长startnos;
静态长源;
静止的{
initNanos();
}
私有静态void initNanos(){
long millisBefore=System.currentTimeMillis();
长毫秒;
做{
startNanos=System.nanoTime();
millisAfter=System.currentTimeMillis();
}而(毫秒数!=毫秒数之前);
firstNanoOrigin=(长)(毫秒后-(startNanos/1e6));
}
静态NumberFormat lnf=DecimalFormat.getNumberInstance();
静止的{
lnf.setMaximumFractionDigits(3);
lnf.setGroupingUsed(真);
};
静态类时间一致性{
长源;
长期起源;
长nummitchtolast=0;
长nummitchtofirst=0;
long numMismatchToFirstBig=0;
长numChecks=0;
公共时间一致性(长源){
firstOrigin=firstNanoOrigin;
lastOrigin=firstOrigin;
}
}
公共静态void main(字符串[]args){
线程[]线程=新线程[最大线程];
对于(int i=0;i大偏移量){
tc.numMismatchToFirstBig++;
}
}
}
现在我做了一些小的改变。基本上,我将nanoTime调用括在两个currentTimeMillis调用之间,以查看线程是否已被重新调度(这应该需要mor)
// ______ delay _______
// v v
long origin = (long)(System.currentTimeMillis() - System.nanoTime() / 1e6);
// ^
// truncation
public class SimpleTimeCoherencyTest {
public static void main(String[] args) {
final long anchorNanos = System.nanoTime();
long lastNanoTime = System.nanoTime();
long accumulatedNanos = lastNanoTime - anchorNanos;
long numCallsSinceAnchor = 1L;
for(int i = 0; i < 100; i++) {
TestRun testRun = new TestRun(accumulatedNanos, lastNanoTime);
Thread t = new Thread(testRun);
t.start();
try {
t.join();
} catch(InterruptedException ie) {}
lastNanoTime = testRun.lastNanoTime;
accumulatedNanos = testRun.accumulatedNanos;
numCallsSinceAnchor += testRun.numCallsToNanoTime;
}
System.out.println(numCallsSinceAnchor);
System.out.println(accumulatedNanos);
System.out.println(lastNanoTime - anchorNanos);
}
static class TestRun
implements Runnable {
volatile long accumulatedNanos;
volatile long lastNanoTime;
volatile long numCallsToNanoTime;
TestRun(long acc, long last) {
accumulatedNanos = acc;
lastNanoTime = last;
}
@Override
public void run() {
long lastNanos = lastNanoTime;
long currentNanos;
do {
currentNanos = System.nanoTime();
accumulatedNanos += currentNanos - lastNanos;
lastNanos = currentNanos;
numCallsToNanoTime++;
} while(currentNanos - lastNanoTime <= 100000000L);
lastNanoTime = lastNanos;
}
}
}