FileChannel tryLock()方法是检查锁还是只是打破它们？

Question

我有两个进程可以查看相同的文件,并希望实现文件锁定.问题似乎是一个进程用java编写而另一个进程用C编写,并且不清楚java端如何实现低级锁定.该平台是Solaris 10.我尝试在文件上引入锁定,以防止在C进程读取文件时Java进程进行更新.我的想法是尝试从java代码中获取一次锁定10次,然后才无条件地写入文件(我假设锁定类型是一个咨询锁定).但是,java tryLock()会在第二次尝试时中断C进程的锁定并破坏读取.

这是代码,简化(Java):

    int iAttemptCnt = 0;
              FileChannel wchannel = new FileOutputStream(new File(fileName), false).getChannel();;
              FileLock flock;
    while(true){
        try{
            MyLog.log(MyLog.LVL_INFO, "attempt to lock  file");
            if( (flock = wChannel.tryLock()) == null ){
                // lock held by another program
                if(++iAttemptCnt >= 10 
                    break;                  
            }
            else{
                MyLog.log(MyLog.LVL_INFO, " file locked");
                break;
            }
        }catch(OverlappingFileLockException ofle){
            .......                     
            if(++iAttemptCnt >= 10 ){
            ...
                break;          
            }                   
        }catch(IOException ioe){
            throw new IOException("failed to lock the  file");
        }
        try{
            MyLog.log(MyLog.LVL_INFO, "File already locked, retrying in one second");
            Thread.sleep(1000);
        }catch(InterruptedException ie){
            .....
        }

    }

C代码使用fcntl:

fd = open(filename, O_RDONLY);

.....

lck.l_type = F_RDLCK;/* F_RDLCK setting a shared or read lock */ 

lck.l_whence = 0; /* offset l_start from beginning of file */ 

lck.l_start = 0LL; 

lck.l_len = 0LL; /* until the end of the file address space */ 

....

while(  fcntl(fd, F_SETLK64, &lck) < 0){ 

  if( errno == EAGAIN )

    ....    
  else if (errno == EIO )

     ...

  else if( errno == ENOLCK)

     ...

  else if (errno == EDEADLK)

     ...
  if(++ii == 10 ){     

    break;
  }

  ...    

  sleep(1);
} 

 MyLongLastingRead();

...
lck.l_type = F_UNLCK;

fcntl(fd, F_SETLK, &lck);

close(fd);

是否tryLock()真的检查锁？

Answer 1

我不确定这是否能解决您的问题，但在我看到的集群结构的 l_pid 字段设置如下的示例中。

fl.l_pid = getpid();

在你的问题中，你没有设置这个字段。尝试看看是否有什么不同。我希望它有帮助。