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From "Steffen Heil" <li...@steffen-heil.de>
Subject AW: OFFTOPIC: Java String problem - possible VM bug
Date Mon, 30 Aug 2010 23:01:55 GMT
Hi

> What version tomcat?

I see this under 6.0.29 [and I think under 6.0.18 before, but I am not
sure], but as this is pure java code, not calling any tomcat code and not
probably affected by tomcat code, I don't think that matters. (That's why I
labeled that off-topic.)

However, if it even could be of any help solving this mystery, I will
provide any information needed.

Regards,
  Steffen

> 
> 
> On Mon, Aug 30, 2010 at 3:38 PM, Steffen Heil <lists@steffen-heil.de>
wrote:
> 
> > Hi
> >
> > I am sorry, I am asking something not really related to tomcat here.
> > While this may sound like a beginners question, I think I really what
> > I am doing in java, but this time I suspect I have found a scenario
> > where the sun/oracle VM exposes a bug with pure String handling.
> >
> > So anyone who can find a bug in the procedure posted below is very
> welcome.
> > So is everyone who can direct me to some place better suited to ask
> > this question.
> >
> > Finding bugs in a static method that only takes immutable arguments
> > usually seems easy... Turns out, it is not.
> >
> > However, please note that I already tried to debug this in various
> > ways and the exception does NOT occur, as soon as a debugger is
> > attached. The exception is only thrown under 64bit Linux Server-VM,
> > within tomcat. It is neither thrown under 64bit Windows, nor on the
> > very same Linux VM as standalone testcase, nor when a debugger is
> > remotely attached. The JREs testest are 1.6u20 and 1.6u21.
> >
> > The code in question is the following:
> >
> >
> >        @SuppressWarnings( "null" )
> >        public final static String replaceAll( String stack, String ...
> > replacements )
> >        {
> >                try {
> >                        if ( stack == null )
> >                                return stack;
> >                        int index, pos;
> >                        String niddle = null, string;
> >                        int niddleLength, stringLength;
> >                        for ( index = 0; true; index += 2 ) {
> >                                if ( index >= replacements.length )
> >                                        return stack;
> >                                niddle = replacements[ index ];
> >                                pos = stack.indexOf( niddle );
> >                                if ( pos != - 1 )
> >                                        break;
> >                        }
> >                        StringBuilder buffer = new StringBuilder( stack
);
> >                        niddleLength = niddle.length();
> >                        string = replacements[ index + 1 ];
> >                        if ( string == null )
> >                                do
> >                                        buffer.delete( pos, pos +
> > niddleLength );
> >                                while ( ( pos = buffer.indexOf( niddle,
> > pos
> > ) ) != - 1 );
> >                        else {
> >                                stringLength = string.length();
> >                                do {
> > /*331*/                         buffer.replace( pos, pos + niddleLength,
> > string );
> >                                        pos += stringLength;
> >                                } while ( ( pos = buffer.indexOf(
> > niddle, pos ) ) != - 1 );
> >                        }
> >                        index += 2;
> >                        for ( ; index < replacements.length; index += 2 )
{
> >                                niddle = replacements[ index ];
> >                                string = replacements[ index + 1 ];
> >                                niddleLength = niddle.length();
> >                                if ( string == null )
> >                                        for ( pos = 0; ( pos =
> > buffer.indexOf( niddle, pos ) ) != - 1; )
> >                                                buffer.delete( pos, pos
> > + niddleLength );
> >                                else {
> >                                        stringLength = string.length();
> >                                        for ( pos = 0; ( pos =
> > buffer.indexOf( niddle, pos ) ) != - 1; pos += stringLength )
> >                                                buffer.replace( pos,
> > pos + niddleLength, string );
> >                                }
> >                        }
> >                        return buffer.toString();
> >                } catch ( Throwable t ) { .... (code to dump the
> > arguments and the stack trace) ...
> >                }
> >        }
> >
> >
> > Note, that when the method is called, there are two arguments: one
> > String and a String[] with a length of 1004 Strings.... (I guarantee
> > that this String array is NOT modified during execution, not even
> > afterwards.) The execption is (it is thrown indirectly in the marked
line 331):
> >
> > java.lang.StringIndexOutOfBoundsException: start > length()
> >        at
> > java.lang.AbstractStringBuilder.replace(AbstractStringBuilder.java:799)
> >        at java.lang.StringBuilder.replace(StringBuilder.java:271)
> >        at
> > com.osiris4.core.utils.StringUtils.replaceAll(StringUtils.java:331)
> >        ....
> >
> >
> > I can provide real arguments that lead to this exception, however, as
> > there are more than 1000 Strings (partially large ones) involved, I
> > will skip them here.
> > Anyone interested will get them by mail. I have various samples.
> >
> >
> > Currently this prevents loading my web application in about one of
> > three times. (And it also happens during internal computations which
> > prevents further work.) Sometimes this error can be "reproduced" (by
> > restarting
> > tomcat) 10 times in a row, sometimes it does not occur within 20
> > restarts at all. (Without changing anything in the systems
> > configuration.)
> >
> >
> > Sorry again, for asking off-topic, but I don't know where to ask for
> > help anymore.
> >
> > Regards,
> >   Steffen
> >
> >

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