[kaffe] RandomAccessFile causes StackOverflowError

Dalibor Topic robilad at yahoo.com
Wed Apr 2 03:27:01 PST 2003

Hi Ito,

--- Ito Kazumitsu <ito.kazumitsu at hitachi-cable.co.jp>
> In message "Re: [kaffe] RandomAccessFile causes
> StackOverflowError"
>     on 03/03/28, Ito Kazumitsu
> <ito.kazumitsu at hitachi-cable.co.jp> writes:
> > > The attached program causes StackOverflowError
> when run with
> > > kaffe
> > And here is a patch.
> The problem is simple.
> The attached programs go into an infinite loop as is
> easily seen.
> And kaffe's read() of java.io.RandomAccessFile and
> some others
> have the same kind of bug.

that made it much clearer, thanks. 

So in short, the problem is that some IO classes
implement read() or read(char/byte[]) by delegating it
directly to read(char/byte[], int, int) which can be
reimplemented in a subclass to call read() or
read(char/byte []), resulting in a circular sequence
of calls blowing up the stack eventually.

You patch elegantly solves the issue by delegating to
an internal worker method _read(char/byte[], int,
int). I'll check it in tonight.

It would be great if you could review other IO code
send me the patches.

In general, the problem can be summed up as:
method M is implemented using overwriteable method N.
Since there is no way to guarantee that N won't be
overwritten to utilize M, the safest way to implement
M and N is to delegate their calls to a private worker
method implementation N' . 

I bet there is a lot of code out there that suffers
from this problem ;)

I'm wondering how to write a program that
automatically tests for this bug pattern ... Or is
there some static checker out there that can do this

I've attached some hand written tests as a start. They
have both discovered new bugs.

dalibor topic

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