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java - 如何知道锁已被获取

转载 作者:行者123 更新时间:2023-12-01 23:45:49 27 4
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我有一个由多个线程访问的通用方法,

     public void m(String fileName)
{
FileOutputStream fos= new FileOutputStream(fileName);
FileChannel fc = fos.getChannel();
fc.tryLock();
....

有时,两个或多个线程中的文件名可能相同,并且当我使用 tryLock() 或 lock() 时会出现异常。我如何知道锁是否已被获取?

更新:

import java.io.FileOutputStream;
import java.nio.channels.FileChannel;

class A implements Runnable{
@Override
public void run()
{
try
{
FileOutputStream fos= new FileOutputStream("file.2txt");
FileChannel fc = fos.getChannel();
fc.tryLock();

Thread.sleep(4000);

fc.close();
System.out.println("done");
}
catch (Exception e)
{
e.printStackTrace();
}
}
}

public class Test
{
public static void main(String[] args) throws Exception
{
new Thread(new A()).start();
Thread.sleep(2000);
new Thread(new A()).start();
}
}

我遇到异常:

java.nio.channels.OverlappingFileLockException
at sun.nio.ch.FileChannelImpl$SharedFileLockTable.checkList(Unknown Source)
at sun.nio.ch.FileChannelImpl$SharedFileLockTable.add(Unknown Source)
at sun.nio.ch.FileChannelImpl.tryLock(Unknown Source)
at java.nio.channels.FileChannel.tryLock(Unknown Source)
at run.A.run(Test.java:14)
at java.lang.Thread.run(Unknown Source)

最佳答案

How can I know if a lock has already been acquired?

最好的答案是使用fc.tryLock();。但是,它不应该抛出异常。如果无法获取锁,它将返回null。这是查看锁是否未锁定的最佳方法。

引用javadocs for FileChannel.tryLock() :

This method does not block. An invocation always returns immediately, either having acquired a lock on the requested region or having failed to do so. If it fails to acquire a lock because an overlapping lock is held by another program then it returns null. If it fails to acquire a lock for any other reason then an appropriate exception is thrown.

关于java - 如何知道锁已被获取,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/17091366/

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