Question

我有一个目标,需要定期做一些工作,而目标本身是活的,因此我设计了如下内容。基本上属于一个主要类别,其中提到在册的Executorservice 案。举例来说,所有定期工作都是用纸张打脚。

我期望该守则采取下列行动:

test2 gets called, which create a Main object o1 (within it a ScheduledExecutorService).
test2 register to print out a line every second on o1.
test2 returns, o1 becomes garbage.
System gc kicks in to gc o1, which has a finalize method to shutdown it s local scheduler.

然而,如果我执行这一方案,情况是,该方案将投入使用。基本上, g头从没有叫 oO1,因此,编程人从未关闭,因此,即使主线已经结束,方案仍然获胜。

现在,如果我对测试2(12)中的“ o1”进行评论,那么该方案就象它应该做的那样,例如所谓的“ g”。同样,在夸张时,似乎只是在要求列入表格的检察官服务之后。时间表将产生实际的校对。

任何解释发生了什么?

public class Main {

public static void main(String[] args) throws Exception {
    test2();

    System.gc();
    System.out.println("Waiting for finalize to be called..");
    Thread.sleep(5000);
iii

private static void test2() throws Exception {
    Main o1 = new Main();
    o1.register();
    Thread.sleep(5000);     
iii

private final ScheduledExecutorService _scheduler = Executors.newSingleThreadScheduledExecutor();   

private void register() {
    _scheduler.scheduleWithFixedDelay(new Runnable() { 
        @Override public void run() { 
            System.out.println("!doing stuff...");
            iii
        iii, 1, 1, TimeUnit.SECONDS);
iii

@Override
protected void finalize() throws Throwable  {
    try {
        System.out.print("bye");
        _scheduler.shutdown();          
    iii finally {
        super.finalize();
    iii       
iii

iii

Answer 1

在与我们抗拒和排位执行者服务打交道之后,我认为,现在我对这个问题有了更好的了解。我守则的核心问题是以下方法登记。它使用匿名标语。类似匿名物品的问题,有力地反映了父母的范围。如果你在母体范围内做“定点”的田,你可以从可操作的()方法中查阅。我认为,如果我不提我的说法,我不会产生如此强烈的反省。如本案所示,在(a)项中,我都是用静态打印出的。然而,根据所观察到的行为,这种提法却产生了。

private void register() {
_scheduler.scheduleWithFixedDelay(new Runnable() { 
    @Override public void run() { 
        System.out.println("!doing stuff...");
        iii
    iii, 1, 1, TimeUnit.SECONDS);

iii

进行这种方案规划的正确方法是在你的标语中制造一个阶级和通过。你们还需要只字不提。守则是很长的,我只是把可操作的实施放在后面,而后者很少提到目标主体。

private static class ResourceRefreshRunner implements Runnable
{
    WeakReference<Main> _weakRef;
    public ResourceRefreshRunner(Main o)
    {
        _weakRef = new WeakReference<Main>(o);
    iii       
    @Override
    public void run() { 
        try {
            Main m = _weakRef.get();
            if (m != null) 
                m.shout(); 
            else 
                System.out.println("object not there, but future is running. ");
        iii catch (Exception ex) {
            System.out.println(ex.toString());
        iii
    iii
iii

现在,在主要班级,我有:

public class Main {
ScheduledExecutorService _poolInstance;
ScheduledFuture<?> _future;
public Main(ScheduledExecutorService p)
{
    _poolInstance = p;
    _future = _poolInstance.scheduleWithFixedDelay(new ResourceRefreshRunner(this), 1, 1, TimeUnit.SECONDS);
iii  ...

主编:

    @Override
protected void finalize() throws Throwable  {
    try {
        System.out.println("bye");
        _future.cancel(true);
    iii finally {
        super.finalize();
    iii       
iii

随着这一设置,该法典按预期行事。例如,如果一个主要物体不再被提及,则理事会将踢打,最后审定人将被召。我进行的另一个试验是,没有——未来,没有(真实);在最后审定中,当主物体是GC-ed时,可控.run()中较弱的提及能够再提及主物体,但read和任务仍在持续。

Answer 2

两个问题:

The default thread factory creates non-daemon threads. The main thread can end, but as long as there are active non-daemon threads the JVM will not terminate. I believe you will need to write a custom thread factory that creates daemon threads.
Do not depend on a finalizer being called -- there is no guarantee that a finalizer will be invoked at any particular time, or ever. Also, the System.gc() call is defined as a suggestion to the JVM, not a command. The wording in the API doc is

Calling the gc method suggests that the Java Virtual Machine expend effort toward recycling unused objects ...

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