Java致命错误SIGSEGV [英] Java fatal error SIGSEGV
问题描述
我从Java编译器收到一条我不明白的错误消息。我已经在OSX 10.6,10.9和Ubuntu 14.04上使用Java 6和7测试了我的代码。当我使用Eclipse调试器或解释器（使用-Xint选项）运行时，一切运行正常。否则，我收到以下消息：
I am getting an error message from the Java compiler that I don't understand. I've tested my code on OSX 10.6, 10.9, and Ubuntu 14.04, with both Java 6 and 7. When I run with the Eclipse debugger or from the interpreter (using -Xint option), everything runs fine. Otherwise, I get the following messages:
Java 1.6：
Invalid memory access of location 0x8 rip=0x1024e9660
Java 1.7：
#
# A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x000000010f7a8262, pid=20344, tid=18179
#
# JRE version: Java(TM) SE Runtime Environment (7.0_60-b19) (build 1.7.0_60-b19)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (24.60-b09 mixed mode bsd-amd64 compressed oops)
# Problematic frame:
# V [libjvm.dylib+0x3a8262] PhaseIdealLoop::idom_no_update(Node*) const+0x12
#
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
#
Java 7的错误输出更多（保存到文件中）但不幸的是我无法将其放入此帖子的字符限制中。
有时候我需要运行我的代码几次才会出现错误，但是它经常出现。
There's more error output for Java 7 (that is saved to a file) but unfortunately I can't fit it in the character limit of this post. Sometimes I need to run my code a couple of times for the error to come up, but it appears more often than not.
我的测试案例涉及缓存一些对数尺度的计算。具体来说，给定log（X），log（Y），...，我有一个小类来计算log（X + Y + ...）。然后我将结果缓存在HashMap中。
My test case involves cacheing some computations in logarithmic scale. Specifically, given log(X),log(Y),..., I have a small class that computes log(X+Y+...). And then I cache the result in a HashMap.
奇怪的是，改变一些循环索引似乎会使问题消失。特别是，如果我替换
Strangely, changing some loop indices seems to make the problem go away. In particular, if I replace
for (int z = 1; z < x+1; z++) {
double logSummand = Math.log(z + x + y);
toReturn.addLogSummand(logSummand);
}
for (int z = 0; z < x; z++) {
double logSummand = Math.log(1 + z + x + y);
toReturn.addLogSummand(logSummand);
}
然后我没有收到错误消息，程序运行正常。
then I don't get the error message and the program runs fine.
我的最小例子如下：
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class TestLogSum {
public static void main(String[] args) {
for (int i = 0; i < 6; i++) {
for (int n = 2; n < 30; n++) {
for (int j = 1; j <= n; j++) {
for (int k = 1; k <= j; k++) {
System.out.println(computeSum(k, j));
}
}
}
}
}
private static Map<List<Integer>, Double> cache = new HashMap<List<Integer>, Double>();
public static double computeSum(int x, int y) {
List<Integer> key = Arrays.asList(new Integer[] {x, y});
if (!cache.containsKey(key)) {
// explicitly creating/updating a double[] array, instead of using the LogSumArray wrapper object, will prevent the error
LogSumArray toReturn = new LogSumArray(x);
// changing loop indices will prevent the error
// in particular, for(z=0; z<x-1; z++), and then using z+1 in place of z, will not produce error
// for (int z = 0; z < x; z++) {
// double logSummand = Math.log(1 + z + x + y);
for (int z = 1; z < x+1; z++) {
double logSummand = Math.log(z + x + y);
toReturn.addLogSummand(logSummand);
}
// returning the value here without cacheing it will prevent the segfault
cache.put(key, toReturn.retrieveLogSum());
}
return cache.get(key);
}
/*
* Given a bunch of logarithms log(X),log(Y),log(Z),...
* This class is used to compute the log of the sum, log(X+Y+Z+...)
*/
private static class LogSumArray {
private double[] logSummandArray;
private int currSize;
private double maxLogSummand;
public LogSumArray(int maxEntries) {
this.logSummandArray = new double[maxEntries];
this.currSize = 0;
this.maxLogSummand = Double.NEGATIVE_INFINITY;
}
public void addLogSummand(double logSummand) {
logSummandArray[currSize] = logSummand;
currSize++;
// removing this line will prevent the error
maxLogSummand = Math.max(maxLogSummand, logSummand);
}
public double retrieveLogSum() {
if (maxLogSummand == Double.NEGATIVE_INFINITY) return Double.NEGATIVE_INFINITY;
assert currSize <= logSummandArray.length;
double factorSum = 0;
for (int i = 0; i < currSize; i++) {
factorSum += Math.exp(logSummandArray[i] - maxLogSummand);
}
return Math.log(factorSum) + maxLogSummand;
}
}
}
推荐答案
因此，在阅读完评论后，似乎这是JVM中需要向Oracle报告的错误。所以，我已经向Oracle提交了一份错误报告。当我收到他们的回复时，我会发布更新。
So after reading the comments, it seems like this is a bug in the JVM that needs to be reported to Oracle. So, I have gone ahead and filed a bug report to Oracle. I'll post updates when I hear back from them.
感谢所有尝试过该代码的人，并发现它在您的机器上也会中断。
Thanks to all those who tried the code and found it breaks on your machines as well.
如果有人有能力/倾向于弄清楚编译器中的代码导致了这个错误，那么听到它会很棒：）
If there is anyone with the ability/inclination to figure out what code in the compiler is causing this error, it would be awesome to hear about it :)
更新：昨天甲骨文有人回复，他说他准备修复了这个bug并要求将我的代码包含为回归测试:)他没有解释什么问题是，除了说它是在HotSpot JIT中，但他确实给我发了一个关于他所做的更改的链接，万一有人感兴趣： http://cr.openjdk.java.net/~kvn/8046516/webrev/
UPDATE: Someone from Oracle responded yesterday, he said he prepared a fix for the bug and also asked to include my code as a regression test :) He didn't explain what the problem was, beyond saying it was in the HotSpot JIT, but he did send me a link with the changes he made, in case anyone is interested: http://cr.openjdk.java.net/~kvn/8046516/webrev/
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