Generate a Java thread dump without restarting.

Question

I\'d like to create a thread that keeps track of the memory usage and cpu usage.

If the application reaches a high level, I want to generate an heap dump or a thread

Answer 1

Try “kill –QUIT” Process_id e.g

kill -QUIT 2134

This will trigger the thread dump without restarting it

Answer 2

Here's how we do it programmatically: http://pastebin.com/uS5jYpd4

We use the JMX ThreadMXBean and ThreadInfo classes:

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

You can also do a kill -QUIT pid under ~unix to dump the stacks to the standard-out. There is also jstack to dump the stack of a JVM.

We also have an automation which dumps the stack if the load average of the application is above some threshold:

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 3

To dump the threads to the standard out, you may do something like this

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

in Java 6 using the ThreadMXBean class. But I would suggest to use real logging instead of the standard output.

Answer 4

Yes, you can generated your own stack dump using the built-in management MXBeans. Specifically, you can get all the current ThreadInfos From the ThreadMXBean and write the contents to your desired location.

Answer 5

In spring application, we can generate heap dump programmatically by creating cron job.

import com.sun.management.HotSpotDiagnosticMXBean;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

import javax.management.MBeanServer;
import java.io.File;
import java.lang.management.ManagementFactory;

@Component
public class HeapDumpGenerator {
    @Scheduled(cron = "0 0/5 * * * *")
    public void execute() {
        generateHeapDump();
    }

    private void generateHeapDump() {
        MBeanServer mBeanServer = ManagementFactory.getPlatformMBeanServer();
        String dumpFilePath = System.getProperty("user.home") + File.separator + 
                "heap-dumps" + File.separator +
                "dumpfile_" + System.currentTimeMillis() + ".hprof";
        try {
            HotSpotDiagnosticMXBean hotSpotDiagnosticMXBean = ManagementFactory
                .newPlatformMXBeanProxy(mBeanServer,
                                    "com.sun.management:type=HotSpotDiagnostic", 
                                    HotSpotDiagnosticMXBean.class);
            hotSpotDiagnosticMXBean.dumpHeap(dumpFilePath, Boolean.TRUE);
        } catch (Exception e) {
            // log error
        }
    }
}

It will run at every five minutes, but we can set our own time/interval. We can also add condition before calling generateHeapDump() method.