File{Input,Output}Stream finalizer should not close FileDescriptor

Name: rm29839 Date: 12/17/97


finalize() method of the FileInputStream and
the FileOutputStream calls close() method,
which closes the FileDescriptor of the
FileInput/OutputStream.
This is good while one FileDescriptor is used
by exactly one FileInput/OutputStream.
If, for example, I open an RandomAccessFile,
get the FileDescriptor, create the
FileInputStream, use FileInputStream and clear
the reference to it, then, when the
FileInputStream will be finalized,
the RandomAccessFile will be inaccessible.
Here the source:

import java.io.*;

public class IOTest extends FileOutputStream
  {

  IOTest(FileDescriptor fd)
    { super(fd); }

  public void close()
    throws IOException
    {
    super.close();
    System.out.println("The file stream is closed");
    }

  protected void finalize()
    throws IOException
    {
    super.finalize();
    System.out.println("The file stream is finalized");
    }

  public static void main(String[] args)
    throws Exception
    {
    RandomAccessFile f = new RandomAccessFile("f", "rw");
    IOTest iot = new IOTest(f.getFD());
    // Do anything with iot, but don't call iot.close() explicitly.
    iot = null;
    // This way to cause finalization seems complicated,
    // but System.runFinalization() don't finalize iot.
    try {
      byte[][] b = new byte[100][];
      for (int i = 0; i < b.length; i++)
        { b[i] = new byte[10000000]; }
      }
    catch (OutOfMemoryError e) {
      }
    f.writeUTF("The string");
    f.close();
    }

  }

Here the output of the program:

The file stream is closed
The file stream is finalized
java.io.IOException: write error
        at java.io.RandomAccessFile.writeUTF(RandomAccessFile.java:842)
        at IOTest.main(IOTest.java:39)

So, f.writeUTF("The string") throws IOException.

As I think, FileInput/OutputStream should not
have finalize() method, because this classes
don't use system resources themself. Instead,
finalize() method should be placed in the class
FileDescriptor.
(Review ID: 22026)
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