[Java NIO] MappedByteBuffer does not write all bytes

[Satish Chilukuri]

I'm seeing some weird behavior with MappedByteBuffer. It only seems to write 1024 * n + 1 bytes ignoring the other bytes. This happens only on an AIX machine. The same code works fine in Windows.

	public static void main(String[] args) {
		try {
			File f = new File("/home/satish/test");
			FileChannel fc = new RandomAccessFile(f, "rw").getChannel();
			int size = new Integer(args[0]);

			StringBuilder builder = new StringBuilder();
			for (int i = 0; i < size; i++) {
				builder.append("A");
			}

			byte[] bytes = builder.toString().getBytes();
			MappedByteBuffer mbb = fc.map(FileChannel.MapMode.READ_WRITE,
					(int) fc.size(), bytes.length);
			mbb.put(ByteBuffer.wrap(bytes));

			fc.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

Here are a few runs with different values for size:

rm -f test; java FileTest 1024; ls -l test
-rw-rw-r--    1 satish  staff             1 May 21 04:31 test

rm -f test; java FileTest 1025; ls -l test
-rw-rw-r--    1 satish  staff          1025 May 21 04:31 test

rm -f test; java FileTest 2048; ls -l test
-rw-rw-r--    1 satish  staff          1025 May 21 04:31 test

rm -f test; java FileTest 2049; ls -l test
-rw-rw-r--    1 satish  staff          2049 May 21 04:31 test

For the first run, the size is 1024 bytes , but only 1 byte is written to the file "test". If the size is between 1025 and 2048, only the first 1025 bytes are written to "test" and so on.

Anyone have any idea as to what is happening here?

[Rob Spoor]

When I try your code on Windows the file size is correct each time. Possibly the flushing does not work well. What happens if you call force() on the MappedByteBuffer?

[Satish Chilukuri]

Rob Prime wrote:When I try your code on Windows the file size is correct each time. Possibly the flushing does not work well. What happens if you call force() on the MappedByteBuffer?

It works in Windows for me too. The problem is in AIX.

I tried calling force() after put(), but the results stay the same.