ByteBuffer.asReadOnlyBuffer() and direct byte buffers

[Erik Larsson <catacombae@gmail.com>]

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Hi group,

In the process of trying to run my JNI-enabled library in gcj/gij I 
discovered what seems to be a bug in libgcj's direct ByteBuffer 
implementation.

When calling ByteBuffer.asReadOnlyBuffer() for a direct byte buffer, gij 
throws at me:
------
Exception in thread "main" java.nio.InvalidMarkException
    at java.nio.Buffer.reset(libgcj.so.10)
    at java.nio.DirectByteBufferImpl.duplicate(libgcj.so.10)
    at java.nio.DirectByteBufferImpl.asReadOnlyBuffer(libgcj.so.10)
    at Test.main(Test.java:18)
------

Test code is attached. The InvalidMarkException goes away if you call 
ByteBuffer.mark() before calling .asReadOnlyBuffer(), but 
.asReadOnlyBuffer() shouldn't require a defined mark (it doesn't for 
regular buffers).

gij version:
------
gij (GNU libgcj) version 4.4.1

Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
------

OS: Ubuntu 9.10 (prerelease), i386

I did a little research, and it seems this bug was reported against 
Classpath in 2005, along with a fix:
      http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22934

The GNU Classpath code contains what seems to be a fix in the current 
revision of DirectByteBufferImpl (duplicate() method):
     
http://cvs.savannah.gnu.org/viewvc/classpath/java/nio/DirectByteBufferImpl.java?revision=1.24&root=classpath&view=markup

...but gcc's libjava doesn't have that particular line ('if (this.mark 
!= -1)'):
     
http://gcc.gnu.org/viewcvs/trunk/libjava/java/nio/DirectByteBufferImpl.java?revision=141271&view=markup

Regards,

- Erik

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import java.nio.ByteBuffer;

public class Test {
    public static void main(String[] args) {
	ByteBuffer bb = ByteBuffer.allocateDirect(1024);
	System.err.println("Created readwrite direct buffer: " + bb);
	//bb.mark(); // Uncomment this line to prevent exception.
	ByteBuffer bbro = bb.asReadOnlyBuffer();
	System.err.println("Created readonly direct buffer: " + bbro);
    }
}