CODEWITHSUNDEEP
javamemory-managementjava-7filechannel
user1717817
user1717817

Reputation:

Java 7 filechannel not closing properly after calling a map method

I'm working on a sc2replay parsing tool. I build it on top of MPQLIB http://code.google.com/p/mpqlib/

Unfortunately the tool uses filechannels to read through the bzip files, and uses map(MapMode.READ_ONLY, hashtablePosition, hashTableSize);

After calling that function closing the file channel does not release the file in the process. To be specific I cannot rename/move the file.

The problem occurs in Java 7 and it works fine on Java 6.

Here is a simple code snippet to replicate it:

    FileInputStream f = new FileInputStream("test.SC2Replay");
    FileChannel fc = f.getChannel();

    fc.map(MapMode.READ_ONLY, 0,1);

    fc.close();

    new File("test.SC2Replay").renameTo(new File("test1.SC2Replay"));

commenting out the fc.map will allow you to rename the file.

P.S. from here Should I close the FileChannel?

It states that you do not need to close both filechannel and filestream because closing one will close another. I also tried closing either or both and still did not worked.

Is there a workaround on renaming the file after reading the data using FileChannel.map on Java 7, because every one seems to have Java 7 nowadays?

Upvotes: 5

Views: 1372

Answers (3)

Hakanai
Hakanai

Reputation: 12680

If you're using Sun JRE, you can cheat by casting to their implementation and telling it to release itself. I'd only recommend doing this if you're not reliant on the file being closed or never plan to use another JRE.

At some point, I hope that something like this will make it into the proper public API.

try (FileInputStream stream = new FileInputStream("test.SC2Replay");
     FileChannel channel = stream.getChannel()) {

    MappedByteBuffer mappedBuffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, 1);
    try {
        // do stuff with it
    } finally {
        if (mappedBuffer instanceof DirectBuffer) {
            ((DirectBuffer) mappedBuffer).cleaner().clean();
        }
    }
}

Upvotes: 0

user1717817
user1717817

Reputation:

Good day,

it seems that FileChannel.map causes the problem on java 7. if you use FileChannel.map, you can no longer close the the file.

a quick work around is instead of using FileChannel.map(MapMode.READ_ONLY, position, length)

you can use

ByteBuffer b = ByteBuffer.allocate(length); 
fc.read(b,position);
b.rewind();

Upvotes: 2

0xCAFEBABE
0xCAFEBABE

Reputation: 5666

It's a documented bug. The bug report referes to Java 1.4, and they consider it a documentation bug. Closing the filechannel does not close the underlying stream.

Upvotes: 0

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