Question

I have a static utility class, FileUtils which has the following method:

public static Object readDataFromInternalStorage(String fileName) 
{...}

public static synchronized void 
          writeDataToInternalStorage(Serializable theData, String fileName) 
{...}

I am encountering the odd java.io.EOFException in my read method when trying to read from internal storage. This is a multi-threaded app where multiple threads can access this code at the same time (though this is not a common case). After thinking about this for a bit, my suspicion is that while reading the file, another thread comes along and writes to the file before the read is finished, thereby mangling the read. Is my assumption correct?

Assuming it is, what is the best way to fix this? Is the answer simply to add ‘synchonized’ to my read method, which if I read this post correctly locks on the entire class?

Answer 1

Your assumption is probably correct; a concurrent write while you are reading can cause all sorts of problems.

One option is to synchronize the read but, as you say, that will allow only one reader or writer at a time. Another option is to use a ReentrantReadWriteLock to control both reading and writing. This is harder to use but is much more flexible, allowing for multiple, simultaneous readers and exclusive writers.