java-进程无法访问文件，因为该文件正在被另一个进程使用 [英] java - The process cannot access the file because it is being used by another process

问题描述

我有一段代码可以监视目录中是否有文件添加.每当将新文件添加到目录时，都会选择文件内容并将其发布在kafka上，然后将其删除.

I have a piece of code that monitors a directory for addition of files. Whenever a new file is added to the directory, the contents of the file are picked and published on kafka and then the file is deleted.

这在我发出单个请求时有效，但是一旦我将代码接受jMeter的5个或10个用户请求，内容就会成功发布到kafka上，但是代码无法删除该文件.我收到一个FileSystemException并显示消息The process cannot access the file because it is being used by another process..

This works when I make a single request but as soon as I subject my code to 5 or 10 user request from jMeter, the contents are published on kafka successfully but the code isn't able to delete the file. I get a FileSystemException with a message that The process cannot access the file because it is being used by another process..

我猜有一些并发问题，我看不到.

I guess there is some concurrency issue which I am unable to see.

public void monitor() throws IOException, InterruptedException {
    Path faxFolder = Paths.get(TEMP_FILE_LOCATION);
    WatchService watchService = FileSystems.getDefault().newWatchService();
    faxFolder.register(watchService, StandardWatchEventKinds.ENTRY_CREATE);
    boolean valid = true;
    do {
        WatchKey watchKey = watchService.take();
        for (WatchEvent<?> event : watchKey.pollEvents()) {
            if (StandardWatchEventKinds.ENTRY_CREATE.equals(event.kind())) {
                String fileName = event.context().toString();
                publishToKafka(new File(TEMP_FILE_LOCATION + fileName).toPath(), "topic");
            }
        }
        valid = watchKey.reset();
    } while (valid);
}

private void publishToKafka(Path path, String topic) {
    try (BufferedReader reader = Files.newBufferedReader(path)) {
        String input = null;
        while ((input = reader.readLine()) != null) {
            kafkaProducer.publishMessageOnTopic(input, topic);
        }
    } catch (IOException e) {
        LOG.error("Could not read buffered file to send message on kafka.", e);
    } finally {
        try {
            Files.deleteIfExists(path); // This is where I get the exception
        } catch (IOException e) {
            LOG.error("Problem in deleting the buffered file {}.", path.getFileName(), e);
        }
    }
}

异常日志:

java.nio.file.FileSystemException: D:\upload\notif-1479974962595.csv: The process cannot access the file because it is being used by another process.

    at sun.nio.fs.WindowsException.translateToIOException(Unknown Source)
    at sun.nio.fs.WindowsException.rethrowAsIOException(Unknown Source)
    at sun.nio.fs.WindowsException.rethrowAsIOException(Unknown Source)
    at sun.nio.fs.WindowsFileSystemProvider.implDelete(Unknown Source)
    at sun.nio.fs.AbstractFileSystemProvider.deleteIfExists(Unknown Source)
    at java.nio.file.Files.deleteIfExists(Unknown Source)
    at com.panasonic.mdw.core.utils.MonitorDirectory$FileContentPublisher.publishToKafka(MonitorDirectory.java:193)
    at com.panasonic.mdw.core.utils.MonitorDirectory$FileContentPublisher.sendData(MonitorDirectory.java:125)
    at com.panasonic.mdw.core.utils.MonitorDirectory$FileContentPublisher.run(MonitorDirectory.java:113)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

推荐答案

看着您的代码，似乎线程选择了一个文件再次发布，而另一个线程选择了它进行发布.这就是为什么没人能删除它的原因. 它必须仅是并发问题.您应该根据以下准则重新设计代码:可以同时运行的步骤和不能同时运行的步骤. 因此，整个过程中的步骤如下:

Looking at your code it seems when one file is picked by thread for publishing again another thread is picking it up for publishing. That's why no one is able to delete it. It must be concurrency issue only. You should redesign code based up on criterion : steps which can be run concurrently and those which cannot be. So steps in the entire process are :

1. 拾取文件(主线程应该这样做)
2. 发布文件(调用其他线程进行操作)
3. 删除文件(称为线程应将其删除)
4. 检查是否存在任何文件(再次主线程可以做到)

此外，选择文件后，您可以将其读入缓冲区，将其删除，然后继续进行发布.这样可以确保主线程不会将此文件分配给其他线程.

Also the moment a file is selected, you can read it into buffer , delete it and then continue with publish. This will make sure that main thread does not assign this file to some other thread.

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