RandomAccessFile & FileInputStream read

[Marlene Miller]

Are RandomAccessFile.read() and FileInputStream.read() related, when the input stream is created using the file descriptor from the random access file?

class Test {
   public static void test() {
      RandomAccessFile file = new RandomAccessFile("db.dat","rw");
      FileDescriptor fd = file.getFD();
      FileInputStream in = new FileInputStream(fd);
      FileOutputStream out = new FileOutputStream(fd);
      //
      file.write(1);
      out.write(2);
      file.seek(0);
      int i1 = in.read();
      int i2 = file.read();
   }
}

(I didn't find any clues in the source code.)

[Jim Yingst]

Hi Marlene! From testing it seems that the two are indeed related. Reading from the RAF seems to advance the file positoin read by the input stream, and vice versa. However I haven't seen any documentation about this. I would guess that this is undocumented behavior, and so it's probably a good idea to avoid code that uses multiple streams and RAFs referring to the same file simultaneously, unless you find explicit documentation somewhere.
In contrast, if you use a FileChannel obtained by the getChannel() method of RAF or a file input or output stream, you do get some explicit guarantees about its behavior relative to the RAF/stream, as well as relative to other FileChannels. There are still some annoying loopholes IMO in terms of shat's guaranteed here and what's not (see this lengthy discussion if you're curious) - but the situation is certainly better than that you originally described, for which there seem to be no guarantees. Unless I missed someting which is entirely possible. Hope that helps...

[Marlene Miller]

Thank you very much Jim (9990 posts, 10 more to go!).
Uh oh. Wrong forum again. Next time, IO and Streams.
>>avoid code that uses multiple streams and RAFs referring to the same file simultaneously
Yes, that was the reason for the question.
Thank you for the link. I will try to understand the whole thing.

[Jim Yingst]

Uh oh. Wrong forum again. Next time, IO and Streams.
And hey, I didn't even have to say anything. Cool.