生成Java线程转储而不重新启动.

Question

我想创建一个跟踪内存使用情况和CPU使用情况的线程.

如果应用程序达到高级别,我想生成堆转储或线程转储.

有没有办法生成线程转储运行时而不重新启动？

Answer 1

以下是我们以编程方式执行的操作:http://pastebin.com/uS5jYpd4

我们使用JMX ThreadMXBean和ThreadInfo类:

ThreadMXBean mxBean = ManagementFactory.getThreadMXBean();
ThreadInfo[] threadInfos = mxBean.getThreadInfo(mxBean.getAllThreadIds(), 0);
...

您还可以使用kill -QUIT pidunder~unix将堆栈转储到标准输出.还有jstack来转储JVM的堆栈.

如果应用程序的负载平均值高于某个阈值,我们还有一个自动转储堆栈:

private long lastCpuTimeMillis;
private long lastPollTimeMillis;

public void checkLoadAverage() {
    long now = System.currentTimeMillis();
    long currentCpuMillis = getTotalCpuTimeMillis();
    double loadAvg = calcLoadAveragePercentage(now, currentCpuMillis);
    if (loadAvg > LOAD_AVERAGE_DUMP_THRESHOLD) {
        try {
            dumpStack("Load average percentage is " + loadAvg);
        } catch (IOException e) {
            // Oh well, we tried
        }
    }
    lastCpuTimeMillis = currentCpuMillis;
    lastPollTimeMillis = now;
}

private long getTotalCpuTimeMillis() {
    long total = 0;
    for (long id : threadMxBean.getAllThreadIds()) {
        long cpuTime = threadMxBean.getThreadCpuTime(id);
        if (cpuTime > 0) {
            total += cpuTime;
        }
    }
    // since is in nano-seconds
    long currentCpuMillis = total / 1000000;
    return currentCpuMillis;
}

private double calcLoadAveragePercentage(long now, long currentCpuMillis) {
    long timeDiff = now - lastPollTimeMillis;
    if (timeDiff == 0) {
        timeDiff = 1;
    }
    long cpuDiff = currentCpuMillis - lastCpuTimeMillis;
    double loadAvg = (double) cpuDiff / (double) timeDiff;
    return loadAvg;
}

Answer 2

要将线程转储到标准输出,您可以执行类似的操作

ThreadInfo[] threads = ManagementFactory.getThreadMXBean()
        .dumpAllThreads(true, true);
for(final ThreadInfo info : threads)
    System.out.print(info);

在Java 6中使用ThreadMXBean类.但我建议使用真正的日志而不是标准输出.