我有一个需要并行计算许多小任务并按照任务的自然顺序处理结果的流程。为此,我有以下设置:
一个简单的ExecutorService,和一个我将用于保存Callable提交到执行程序时返回的Future对象的阻塞队列:
当前线程使用
一个简单的ExecutorService,和一个我将用于保存Callable提交到执行程序时返回的Future对象的阻塞队列:
ExecutorService exec = Executors.newFixedThreadPool(15);
LinkedBlockingQueue<Future<MyTask>> futures = new LinkedBlockingQueue<Future<MyTask>>(15 * 64);
以下是一些调试代码,用于定期计算提交的任务数和处理过的任务数,并将它们写出来(注意,processed
是在任务代码本身结束时递增的):
AtomicLong processed = new AtomicLong(0);
AtomicLong submitted = new AtomicLong(0);
Timer statusTimer = new Timer();
statusTimer.schedule(new TimerTask() {
@Override
public void run() {
l.info("Futures: " + futures.size() + "; Submitted: " + submitted.get() + "; Processed: " + processed.get() + "; Diff: " + (submitted.get() - processed.get())));
}
}, 60 * 1000, 60 * 1000);
一个线程从队列中获取任务(其实是一个生成器),将它们提交给执行者,并将结果Future放入futures
队列中(这样我就能确保不会提交太多任务而导致内存耗尽):
Thread submitThread = new Thread(() ->
{
MyTask task;
try {
while ((task = taskQueue.poll()) != null) {
futures.put(exec.submit(task));
submitted.incrementAndGet();
}
} catch (Exception e) {l .error("Unexpected Exception", e);}
}, "SubmitTasks");
submitThread.start();
当前线程使用
take
方法从futures
队列中取出已完成的任务并处理结果:while (!futures.isEmpty() || submitThread.isAlive()) {
MyTask task = futures.take().get();
//process result
}
当我在一个拥有8个核心的服务器上运行此代码(注意,代码当前使用了15个线程),CPU利用率仅达到峰值约为60%。我会看到这样的调试输出:
INFO : Futures: 960; Submitted: 1709710114; Processed: 1709709167; Diff: 947
INFO : Futures: 945; Submitted: 1717159751; Processed: 1717158862; Diff: 889
INFO : Futures: 868; Submitted: 1724597808; Processed: 1724596954; Diff: 853
INFO : Futures: 940; Submitted: 1732030120; Processed: 1732029252; Diff: 871
INFO : Futures: 960; Submitted: 1739538576; Processed: 1739537758; Diff: 818
INFO : Futures: 960; Submitted: 1746965761; Processed: 1746964811; Diff: 950
线程转储显示,许多线程池线程像这样阻塞:
"pool-1-thread-14" #30 prio=5 os_prio=0 tid=0x00007f25c802c800 nid=0x10b2 waiting on condition [0x00007f26151d5000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00007f2fbb0001b0> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireInterruptibly(AbstractQueuedSynchronizer.java:897)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(AbstractQueuedSynchronizer.java:1222)
at java.util.concurrent.locks.ReentrantLock.lockInterruptibly(ReentrantLock.java:335)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:439)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
我的理解是,任何时候我都至少有几百个任务已经提交给执行器服务,但没有被处理(通过堆栈跟踪我也可以确认SubmitTasks线程在LinkedBlockingQueue.put上被阻塞)。然而,堆栈跟踪(以及服务器利用率统计)显示执行器服务在LinkedBlockingQueue.take上被阻塞(我假设这是内部任务队列为空的情况)。
我错在哪里了?