线程“main”java.lang.OutofMemoryError中出现异常：无法创建新的本机线程

Question

Exception in thread "main" java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Thread.java:717)
at java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:950)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1357)
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:134)
at com.albertoborsetta.formscanner.api.FormTemplate.findPoints(FormTemplate.java:852)
at com.albertoborsetta.formscanner.model.FormScannerModel.analyzeFiles(FormScannerModel.java:562)
at com.albertoborsetta.formscanner.main.FormScanner.main(FormScanner.java:145)

public void findPoints(BufferedImage image, int threshold, int density,
        int size) throws FormScannerException {
    height = image.getHeight();
    width = image.getWidth();
    int cores = Runtime.getRuntime().availableProcessors();

    ExecutorService threadPool = Executors.newFixedThreadPool(cores - 1);
    HashSet<Future<HashMap<String, FormQuestion>>> fieldDetectorThreads = new HashSet<>();

    HashMap<String, FormQuestion> templateFields = template.getFields();
    ArrayList<String> fieldNames = new ArrayList<>(templateFields.keySet());
    Collections.sort(fieldNames);

    for (String fieldName : fieldNames) {
        Future<HashMap<String, FormQuestion>> future = threadPool.submit(new FieldDetector(threshold, density, size, this, templateFields.get(fieldName), image));
        fieldDetectorThreads.add(future);
    }

    for (Future<HashMap<String, FormQuestion>> thread : fieldDetectorThreads) {
        try {
            HashMap<String, FormQuestion> threadFields = thread.get();
            for (String fieldName : threadFields.keySet()) {
                FormQuestion field = threadFields.get(fieldName);
                fields.put(fieldName, field);
                for (Entry<String, FormPoint> point : field.getPoints().entrySet()) {
                    if (point.getValue() != null) {
                        pointList.add(point.getValue());
                    }
                }
            }
        } catch (InterruptedException | ExecutionException e) {
            throw new FormScannerException(e.getCause());
        }
    }

    threadPool.shutdown();

}

在调用shutdown方法后，这些线程是否会被杀死。我不是java开发人员。我做了一些研发。但我不成功。

Answer 1

问题来自集 用来保存每个实例以便以后检查它们。

在聊天中，你告诉我你正在检查120.000个文件。这意味着有许多未来创建，当池找到一个插槽时，它将创建一个线程来执行可调用的。

因为集保存每个实例，所以线程不会被垃圾回收，这就是泄漏的原因。您需要删除所有使用的future，以便GC为下一个线程清除内存。

Iterator<Future<HashMap<String, FormQuestion>>> iterator = fieldDetectorThreads.iterator();
while (iterator.hasNext()) {
    //get the next instance
    Future<HashMap<String, FormQuestion>> thread = iterator.next();
    //Remove it from the set
    iterator.remove();

    //then work on that instance just like before
    try {
        HashMap<String, FormQuestion> threadFields = thread.get();
        for (String fieldName : threadFields.keySet()) {
            FormQuestion field = threadFields.get(fieldName);
            fields.put(fieldName, field);
            for (Entry<String, FormPoint> point : field.getPoints().entrySet()) {
                if (point.getValue() != null) {
                    pointList.add(point.getValue());
                }
            }
        }
    } catch (InterruptedException | ExecutionException e) {
        throw new FormScannerException(e.getCause());
    }
}

但是，如果提交请求的循环花了很长时间才结束（在检查第一个请求之前生成120k未来），那么在发送每个请求之前，这个循环就会中断。

在这种情况下，可能需要将该逻辑拆分为两个线程，一个用于发送请求，一个用于检查结果，直到第一个线程结束并且集合为空。

以防万一，我会在循环之后添加一个关闭请求

threadPool.shutdown();