我正在使用ConcurrentLinkedQueue来存储计算步骤，并使用ExecutorService创建的Executors.newFixedThreadPool来执行它们。我的问题是应用程序永远不会终止。这是一些代码：
public class Run {
public static void main (String[] args) throws Exception {
ParallelExecutor executor = new ParallelExecutor();
executor.execute();
// manual shutdown
Thread.sleep(30 * 1000);
executor.stop();
// the main thread dies, the application keeps running
}
public class ParallelExecutor implements Runnable {
// stores executions steps to
private ConcurrentLinkedQueue<ExecutionStep> queue = new ConcurrentLinkedQueue<ExecutionStep>();
private ExecutorService threadPoolExecutor = Executors.newFixedThreadPool(10);
private Thread feedingThread = new Thread(this);
public void execute() {
ExecutionStep step = new ConcreteExecutionStep();
this.queue.add(step);
this.feedingThread.start();
}
public void stop() {
if (log.isInfoEnabled()) {
log.info("Shutting down");
}
this.queue = new ConcurrentLinkedQueue<ExecutionStep>();
try {
this.feedingThread.join(0);
this.threadPoolExecutor.shutdownNow();
} catch (InterruptedException e) {
log.warn("Something happened!", e);
}
}
public void run() {
while (true) {
if (this.threadPoolExecutor.isShutdown()) {
return;
}
try {
Thread.sleep(this.waitMillis);
} catch (InterruptedException e) {
// NOP
}
if (!this.queue.isEmpty()) {
this.threadPoolExecutor.execute(new Runnable() {
@Override
public void run() {
ExecutionStep step = this.queue.poll();
List<ExecutionStep> nextSteps = Collections.emptyList();
try {
nextSteps = step.execute();
} catch (Exception e) {
// NOP
}
// here we feed the queue
this.queue.addAll(nextSteps);
}
});
}
}
}
编辑：这是主线程死亡后的线程转储：
2011-09-06 17:20:56
Full thread dump Java HotSpot(TM) 64-Bit Server VM (20.1-b02-384 mixed mode):
"DestroyJavaVM" prio=5 tid=10f874800 nid=0x100501000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE
"Poller SunPKCS11-Darwin" daemon prio=1 tid=101a4d800 nid=0x11362e000 waiting on condition [11362d000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at sun.security.pkcs11.SunPKCS11$TokenPoller.run(SunPKCS11.java:692)
at java.lang.Thread.run(Thread.java:680)
"pool-2-thread-1" prio=5 tid=103db3000 nid=0x11341a000 waiting on condition [113419000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <7f42e8f38> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1987)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:399)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:947)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:680)
"Timer-0" daemon prio=5 tid=101a63000 nid=0x113317000 in Object.wait() [113316000]
java.lang.Thread.State: TIMED_WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <7f49cc200> (a java.util.TaskQueue)
at java.util.TimerThread.mainLoop(Timer.java:509)
- locked <7f49cc200> (a java.util.TaskQueue)
at java.util.TimerThread.run(Timer.java:462)
"Low Memory Detector" daemon prio=5 tid=10180a000 nid=0x10f607000 runnable [00000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread1" daemon prio=9 tid=101809800 nid=0x10f504000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" daemon prio=9 tid=103951000 nid=0x10f401000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE
"JDWP Command Reader" daemon prio=5 tid=103950000 nid=0x10df01000 runnable [00000000]
java.lang.Thread.State: RUNNABLE
"JDWP Event Helper Thread" daemon prio=5 tid=10394f800 nid=0x10dc0a000 runnable [00000000]
java.lang.Thread.State: RUNNABLE
"JDWP Transport Listener: dt_socket" daemon prio=5 tid=10394e800 nid=0x10db07000 runnable [00000000]
java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" daemon prio=9 tid=10e000000 nid=0x10da04000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE
"Surrogate Locker Thread (Concurrent GC)" daemon prio=5 tid=101808800 nid=0x10d901000 waiting on condition [00000000]
java.lang.Thread.State: RUNNABLE
"Finalizer" daemon prio=8 tid=10393f000 nid=0x10c204000 in Object.wait() [10c203000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <7f44e3d70> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:118)
- locked <7f44e3d70> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:134)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)
"Reference Handler" daemon prio=10 tid=10393e000 nid=0x10c101000 in Object.wait() [10c100000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <7f44e5220> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:485)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116)
- locked <7f44e5220> (a java.lang.ref.Reference$Lock)
"VM Thread" prio=9 tid=103939800 nid=0x10b6fc000 runnable
"Gang worker#0 (Parallel GC Threads)" prio=9 tid=103801800 nid=0x102601000 runnable
"Gang worker#1 (Parallel GC Threads)" prio=9 tid=103802000 nid=0x102704000 runnable
"Gang worker#2 (Parallel GC Threads)" prio=9 tid=103803000 nid=0x107102000 runnable
"Gang worker#3 (Parallel GC Threads)" prio=9 tid=103803800 nid=0x107205000 runnable
"Gang worker#4 (Parallel GC Threads)" prio=9 tid=103804000 nid=0x107308000 runnable
"Gang worker#5 (Parallel GC Threads)" prio=9 tid=103804800 nid=0x10740b000 runnable
"Gang worker#6 (Parallel GC Threads)" prio=9 tid=103805800 nid=0x10750e000 runnable
"Gang worker#7 (Parallel GC Threads)" prio=9 tid=103806000 nid=0x107611000 runnable
"Concurrent Mark-Sweep GC Thread" prio=9 tid=1038e3800 nid=0x10b408000 runnable
"Gang worker#0 (Parallel CMS Threads)" prio=9 tid=1038e2000 nid=0x10aa02000 runnable
"Gang worker#1 (Parallel CMS Threads)" prio=9 tid=1038e2800 nid=0x10ab05000 runnable
"VM Periodic Task Thread" prio=10 tid=10181c000 nid=0x10f70a000 waiting on condition
"Exception Catcher Thread" prio=10 tid=103801000 nid=0x1017f9000 runnable
JNI global references: 13614
Heap
par new generation total 19136K, used 16017K [7f3000000, 7f44c0000, 7f44c0000)
eden space 17024K, 81% used [7f3000000, 7f3d944a8, 7f40a0000)
from space 2112K, 100% used [7f42b0000, 7f44c0000, 7f44c0000)
to space 2112K, 0% used [7f40a0000, 7f40a0000, 7f42b0000)
concurrent mark-sweep generation total 63872K, used 6053K [7f44c0000, 7f8320000, 7fae00000)
concurrent-mark-sweep perm gen total 30656K, used 30476K [7fae00000, 7fcbf0000, 800000000)
编辑：问题是由于另一个执行者在发布问题之前在我删除的代码中（默默地）启动，因为我认为这无关紧要。无论如何，Peter Lawrey答案仍然是有价值的输入，因此它被接受了。
答案 0 :(得分：3)
在关闭执行程序之前，您正在等待fedThread终止（feedingThread.join(0)），并且进给线程将在while（true）-loop中继续，直到执行程序停止。
答案 1 :(得分：2)
这将关闭，前提是没有工作正在进行，并且它不会不时地暂停，这会减慢您的应用程序速度，并且可能使其看起来没有任何结果。
public class ParallelExecutor {
interface ExecutionStep {
List<ExecutionStep> execute();
}
public static final int N_THREADS = Runtime.getRuntime().availableProcessors();
private final ExecutorService executorService = Executors.newFixedThreadPool(N_THREADS);
public void execute(final ExecutionStep step) {
executorService.submit(new Runnable() {
@Override
public void run() {
for (ExecutionStep es : step.execute())
execute(es);
}
});
}
public void stop() {
this.executorService.shutdownNow();
}
}
用
运行ParallelExecutor executor = new ParallelExecutor();
executor.execute(new ConcreteExecutionStep());
// manual shutdown
Thread.sleep(30 * 1000);
executor.stop();
答案 2 :(得分：0)
我找到了一个非常简单的答案。如果您不是从主函数返回，而是以System.exit(0)结束，则执行程序将按预期死亡。