ByteBuffer.asReadOnlyBuffer() and direct byte buffers

Erik Larsson catacombae@gmail.com
Sat Oct 3 04:30:00 GMT 2009


Hi,

Should I report this somewhere else?

- Erik

Erik Larsson wrote:
> 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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