我正在使用 Java ExecutorService (ThreadPool) 来执行任务并更新 UI,同时特定 Activity 位于前台(可见)。
问题: 我想要的是,当用户切换到另一个 Activity 时,我想停止/取消所有任务(无论是排队还是正在运行)。为此,我必须在调用 isDone() 检查 Future 对象状态后,对 ExecutorService 提交方法返回的 Future 对象使用 ExecutorService shutdown/shutdownNow 方法或 cancel(true) 。这会将相应的中断线程标志设置为 TRUE,我必须在可调用实现中检查(Thread.currentThread.isInterrupted())以确定是否被中断退出任务/线程。问题是我是否调用 ExecutorService shutdown 方法或 Future cancel(true) 方法,在这两种情况下,很少有 10 次中有 1 次它将线程中断标志设置为 TRUE,这最终导致内存泄漏等。
代码:
ThreadPool Singleton实现(cancelAll-取消任务& shutdownExecutor-关闭ExecutorService):
private static class ThreadPoolManager {
private ExecutorService executorService;
private List<Future> queuedFutures;
private BlockingQueue<Runnable> blockingQueue;
private static ThreadPoolManager instance;
private ThreadPoolManager() {
MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Threadpool-created(constructor)");
queuedFutures = new ArrayList<>();
blockingQueue = new LinkedBlockingDeque<>();
executorService = new ThreadPoolExecutor(Runtime.getRuntime().availableProcessors(), Runtime.getRuntime().availableProcessors(), 1, TimeUnit.SECONDS, blockingQueue);
}
static {
instance = new ThreadPoolManager();
}
public static void submitItemTest(Callable<Object> callable) {
MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Threadpool-submitted item test");
if(instance.executorService.isShutdown()){
instance=new ThreadPoolManager();
}
Future future = instance.executorService.submit(callable);
instance.queuedFutures.add(future);
}
public static void submitTestAll(Callable<Object> callable) {
MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Threadpool-submitted test all");
if(instance.executorService.isShutdown()){
instance=new ThreadPoolManager();
}
cancelAll();
Future future = instance.executorService.submit(callable);
instance.queuedFutures.add(future);
}
public static void cancelAll() {
MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Cancelling all future tasks");
instance.blockingQueue.clear();
for (Future future : instance.queuedFutures) {
if (!future.isDone()) {
boolean cancelled = future.cancel(true);
MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Cancelled-" + cancelled);
}
}
instance.queuedFutures.clear();
}
public static void shutdownExecutor(){
MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Shuttingdown threadpool");
instance.executorService.shutdownNow();
}
}
可调用实现(正常迭代和检查中断的 if 子句):
private Callable<Object> getTestAllCallable() {
return new Callable<Object>() {
@Override
public Object call() {
for (int i = 0; i < inbuiltProxyPojoArrayList.size(); i++) {
if (!Thread.currentThread().isInterrupted()) {
//someWork
} else {
MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "ThreadInterrupted-Cancelling");
return null;
}
}
return null;
}
};
}
Activity/Fragment onStop 实现(用于调用取消任务和关闭):
@Override
public void onStop() {
MyLogger.log(MyLogger.LOG_TYPE.INFO, "onStop called");
ThreadPoolManager.cancelAll();
ThreadPoolManager.shutdownExecutor();
super.onStop();
}
更新:
所做的更改:
不再使用 Runnable 而不是 Callable。
现在不再对 ExecutorService 使用单例。
private class ThreadPoolManager { private ExecutorService executorService; private List<Future> queuedFutures; private BlockingQueue<Runnable> blockingQueue; private ThreadPoolManager() { MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Threadpool-created(constructor)"); queuedFutures = new ArrayList<>(); blockingQueue = new LinkedBlockingDeque<>(); executorService =getNewExecutorService(); } private ExecutorService getNewExecutorService(){ return new ThreadPoolExecutor(Runtime.getRuntime().availableProcessors(), Runtime.getRuntime().availableProcessors(), 1, TimeUnit.SECONDS, blockingQueue); } private void submitItemTest(Runnable runnable) { MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Threadpool-submitted item test"); if(executorService.isShutdown()){ executorService=getNewExecutorService(); } Future future = executorService.submit(runnable); queuedFutures.add(future); } private void submitTestAll(Runnable runnable) { MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Threadpool-submitted test all"); if(executorService.isShutdown()){ executorService=getNewExecutorService(); } cancelAll(); Future future = executorService.submit(runnable); queuedFutures.add(future); } private void cancelAll() { MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Cancelling all future tasks"); blockingQueue.clear(); for (Future future : queuedFutures) { if (!future.isDone()) { boolean cancelled = future.cancel(true); MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Cancelled-" + cancelled); } } queuedFutures.clear(); } private void shutdownExecutor(){ MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Shuttingdown threadpool"); executorService.shutdownNow(); blockingQueue.clear(); queuedFutures.clear(); } }
找到了罪魁祸首,但还没有找到解决方案。以下 2 是 Runnables 1 的实现,其中 1 正在运行(isInterrupted 返回 true 或出现 InterupptedException,然后任务结束),但其他则不运行。
工作可运行(我用它来测试):
new Runnable() {
@Override
public void run() {
int i=0;
while(!Thread.currentThread().isInterrupted()){
try {
System.out.println(i);
Thread.currentThread().sleep(2000);
} catch (InterruptedException e) {
MyLogger.log(MyLogger.LOG_TYPE.DEBUG,"Interrupted");
return;
}
i++;
}
}
}
不工作(我想使用的实际代码):
new Runnable(){
@Override
public void run() {
for (int i = 0; i < inbuiltProxyPojoArrayList.size(); i++) {
if (!Thread.currentThread().isInterrupted()) {
} else {
MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "Thread Interrupted (Cancelled)");
break;
}
}
}
};
1 个可能的解决方案是使用变量( boolean 值)作为可运行对象内的中断标志,我将其视为最后的手段,但很乐意了解错误。
最佳答案
根据 ExecutorService
文档,关闭正在执行的任务是尽最大努力完成的。
因此,当您调用 ExecutorService.shutdownNow()
时,实现将尝试关闭所有当前正在执行的任务。每个任务将继续运行,直到它检测到它被中断为止。
为了确保您的线程在早期阶段达到该点,最好在循环中添加检查线程是否被中断,如下所示:
Thread.currentThread().isInterrupted();
通过在每次迭代时进行此调用,您的线程将在距实际中断很短的间隔内检测到中断。
因此,修改后的 Callable
代码将如下所示:
private Callable<Object> getTestAllCallable() {
return new Callable<Object>() {
@Override
public Object call() {
for (int i = 0; i < inbuiltProxyPojoArrayList.size(); i++) {
if(Thread.currentThread().isInterrupted()) {
return null;
}
if(someCondition) {
//someWork
} else {
MyLogger.log(MyLogger.LOG_TYPE.DEBUG, "ThreadInterrupted-Cancelling");
return null;
}
}
return null;
}
};
}
顺便说一句,如果您不打算从 call()
方法返回任何值,则使用 Callable
是没有意义的。如果您的任务中需要参数化类型,只需创建一个参数化 Runnable
即可,如下所示:
public class ParameterizedRunnable<T> implements Runnable {
private final T t;
public ParameterizedRunnable(T t) {
this.t = t;
}
public void run() {
//do some work here
}
}
关于Java ExecutorService - 任务/可调用不取消/中断,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45390151/