为了了解某些东西如何扩展,我会尽力将监控成本保持在最低限度,并且我会比较一个小数字和一个大数字。
public class Executor_Demo {
public static void main(String... arg) throws ExecutionException, InterruptedException {
int nThreads = 5100;
ExecutorService executor = Executors.newFixedThreadPool(nThreads, new DaemonThreadFactory());
List<Future<Results>> futures = new ArrayList<Future<Results>>();
for (int i = 0; i < nThreads; i++) {
futures.add(executor.submit(new BackgroundCallable()));
}
Results result = new Results();
for (Future<Results> future : futures) {
result.merge(future.get());
}
executor.shutdown();
result.print(System.out);
}
static class Results {
private long cpuTime;
private long userTime;
Results() {
final ThreadMXBean tb = ManagementFactory.getThreadMXBean();
cpuTime = tb.getCurrentThreadCpuTime();
userTime = tb.getCurrentThreadUserTime();
}
public void merge(Results results) {
cpuTime += results.cpuTime;
userTime += results.userTime;
}
public void print(PrintStream out) {
ThreadMXBean tb = ManagementFactory.getThreadMXBean();
List<MemoryPoolMXBean> pools = ManagementFactory.getMemoryPoolMXBeans();
for (int i = 0, poolsSize = pools.size(); i < poolsSize; i++) {
MemoryPoolMXBean pool = pools.get(i);
MemoryUsage peak = pool.getPeakUsage();
out.format("Peak %s memory used:\t%,d%n", pool.getName(), peak.getUsed());
out.format("Peak %s memory reserved:\t%,d%n", pool.getName(), peak.getCommitted());
}
out.println("Total thread CPU time\t" + cpuTime);
out.println("Total thread user time\t" + userTime);
out.println("Total started thread count\t" + tb.getTotalStartedThreadCount());
out.println("Current Thread Count\t" + tb.getThreadCount());
out.println("Peak Thread Count\t" + tb.getPeakThreadCount());
out.println("Daemon Thread Count\t" + tb.getDaemonThreadCount());
}
}
static class DaemonThreadFactory implements ThreadFactory {
@Override
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setDaemon(true);
return t;
}
}
static class BackgroundCallable implements Callable<Results> {
@Override
public Results call() throws Exception {
Thread.sleep(100);
return new Results();
}
}
}
当测试时-XX:MaxNewSize=64m
(这限制了临时内存空间的大小会增加)
100 threads
Peak Code Cache memory used: 386,880
Peak Code Cache memory reserved: 2,555,904
Peak PS Eden Space memory used: 41,280,984
Peak PS Eden Space memory reserved: 50,331,648
Peak PS Survivor Space memory used: 0
Peak PS Survivor Space memory reserved: 8,388,608
Peak PS Old Gen memory used: 0
Peak PS Old Gen memory reserved: 192,675,840
Peak PS Perm Gen memory used: 3,719,616
Peak PS Perm Gen memory reserved: 21,757,952
Total thread CPU time 20000000
Total thread user time 20000000
Total started thread count 105
Current Thread Count 93
Peak Thread Count 105
Daemon Thread Count 92
5100 threads
Peak Code Cache memory used: 425,728
Peak Code Cache memory reserved: 2,555,904
Peak PS Eden Space memory used: 59,244,544
Peak PS Eden Space memory reserved: 59,244,544
Peak PS Survivor Space memory used: 2,949,152
Peak PS Survivor Space memory reserved: 8,388,608
Peak PS Old Gen memory used: 3,076,400
Peak PS Old Gen memory reserved: 192,675,840
Peak PS Perm Gen memory used: 3,787,096
Peak PS Perm Gen memory reserved: 21,757,952
Total thread CPU time 810000000
Total thread user time 150000000
Total started thread count 5105
Current Thread Count 5105
Peak Thread Count 5105
Daemon Thread Count 5104
主要的增加是旧一代使用量的增加约 3 MB 或每个线程约 6 KB。 CPU 使用时间为 956 毫秒,即每个线程大约 0.2 毫秒。
在第一个示例中,您创建一个线程,在第二个示例中您创建 1000 个线程。
您正在执行的输出似乎是大部分工作,并且第二种情况下的输出比第一种情况要多得多。
您需要确保您的测试和监控比您想要监控/测量的要轻得多。