我需要监控应用程序所创建的线程消耗的内存量。如果某个贪婪的线程消耗了太多的内存,那么就需要采取纠正措施。我参考了How much memory does my java thread take?中的一些建议,其中一个建议是在ThreadMXBean
中使用getThreadAllocatedBytes
。我使用下面的作业来尝试使用getThreadAllocatedBytes
。
List<Long> primes = new ArrayList<Long>();
long i = 0;
while (true) {
primes.add(++i);
if ((i % 10) == 0) {
primes.clear();
System.runFinalization();
System.gc();
}
}
我在四个线程上运行这个任务相当长的时间。尽管该任务不会持续累积内存,但getThreadAllocatedBytes
返回的值却不断增加,甚至从未下降。这意味着getThreadAllocatedBytes
并不返回线程在堆上实际使用的内存量,而是返回自线程启动以来为其分配的堆上总内存量。我的平台细节如下:
Linux PG85213.egi.ericsson.com 3.5.0-030500-generic #201207211835 SMP Sat Jul 21 22:35:55 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)
上述行为是否是getThreadAllocatedBytes
的期望行为?
如果是,那么是否没有办法找到线程有效使用的堆上内存。
参考完整程序如下:
package workbench;
import java.lang.management.ManagementFactory;
import com.sun.management.ThreadMXBean;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executors;
import java.util.logging.Level;
import java.util.logging.Logger;
public class AnotherWorkBench {
private static final CountDownLatch latch = new CountDownLatch(4);
static final List<Long> threadIds = Collections.synchronizedList(new ArrayList<Long>());
private void dummyJob() {
List<Long> primes = new ArrayList<Long>();
long i = 0;
while (true) {
primes.add(++i);
if ((i % 10) == 0) {
primes.clear();
//introduce sleep to prevent process hogging
try {
Thread.currentThread().sleep(2000);
} catch (InterruptedException ex) {
Logger.getLogger(AnotherWorkBench.class.getName()).log(Level.SEVERE, null, ex);
}
System.runFinalization();
System.gc();
}
}
}
private void runDummyJobs() {
Runnable dummyJob = new Runnable() {
@Override
public void run() {
threadIds.add(Thread.currentThread().getId());
latch.countDown();
dummyJob();
}
};
Runnable memoryMonitorJob = new Runnable() {
@Override
public void run() {
System.out.println(Thread.currentThread().getName() + " : Monitor thread started");
ThreadMXBean threadMxBean = (ThreadMXBean) ManagementFactory.getThreadMXBean();
threadMxBean.setThreadAllocatedMemoryEnabled(true);
while (true) {
for (Long threadId : threadIds) {
System.out.println(Thread.currentThread().getName() + " : Thread ID : " + threadId + " : memory = " + threadMxBean.getThreadAllocatedBytes(threadId) + " bytes");
}
//wait between subsequent scans
try {
System.out.println(Thread.currentThread().getName() + " : secondary sleep");
Thread.currentThread().sleep(5000);
System.out.println(Thread.currentThread().getName() + " : out of secondary sleep");
} catch (InterruptedException ex) {
Logger.getLogger(WorkBench.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
};
Executors.newSingleThreadExecutor().submit(dummyJob);
Executors.newSingleThreadExecutor().submit(dummyJob);
Executors.newSingleThreadExecutor().submit(dummyJob);
Executors.newSingleThreadExecutor().submit(dummyJob);
try {
latch.await();
} catch (InterruptedException ex) {
Logger.getLogger(AnotherWorkBench.class.getName()).log(Level.SEVERE, null, ex);
}
Executors.newSingleThreadExecutor().submit(memoryMonitorJob);
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
new AnotherWorkBench().runDummyJobs();
}
}
System.gc()
并不保证GC一定会运行。特别是在您的情况下,System.gc()
可能会以亚毫秒间隔调用,虚拟机可能会决定将GC运行推迟到某个任意时间;通常是当可用内存按某种度量变得较低时。 - JimmyB