bug 8014477 Race in String.contentEquals

[Mike Duigou]

Hi Peter;

I tried it on my i7 box and was able to get it to fail right away. I didn't try the previous test on this box so can't say whether it would have also failed.

Applying the String changes resolved the issue. I think this one is ready!

Mike

On May 15 2013, at 00:50 , Peter Levart wrote:

> Mike, David,
> 
> Could you try this variant of the test:
> 
> http://cr.openjdk.java.net/~plevart/jdk8-tl/String.contentEquals/webrev.05/
> 
> 
> I tried it on 3 different machines (4-core i7 Linux, 8-core sparc T-2 Solaris, 4-core amd64 Solaris) x 2 different JDK8 JVMs (64bit and 32bit) and it fails immediately on all 6 of them.
> 
> Regards, Peter
> 
> On 05/14/2013 05:39 PM, Mike Duigou wrote:
>> Good to see the test added. I was also unable to reproduce the failure on my Core 2 Duo Mac laptop but the test and fix match up.
>> 
>> Mike
>> 
>> 
>> On May 14 2013, at 04:34 , Peter Levart wrote:
>> 
>>> On 05/14/2013 01:17 PM, David Holmes wrote:
>>>> Thanks Peter this looks good to me.
>>>> 
>>>> One minor thing please set the correct copyright year in the test, it should just be
>>>> 
>>>> Copyright (c) 2013, Oracle ...
>>> Ok, fixed:
>>> 
>>> http://cr.openjdk.java.net/~plevart/jdk8-tl/String.contentEquals/webrev.04/
>>> 
>>> 
>>>> I couldn't get the test to actually fail, but I can see that it could.
>>> Hm, do you have a multi-core chip? On my computer (i7 CPU) it fails immediately and always. You could try varying the number of concurrent threads and or the time to wait for exception to be thrown...
>>> 
>>>> David
>>>> 
>>>> On 14/05/2013 9:04 PM, Peter Levart wrote:
>>>>> Ok, here's the corrected fix:
>>>>> 
>>>>> http://cr.openjdk.java.net/~plevart/jdk8-tl/String.contentEquals/webrev.03/
>>>>> 
>>>>> I also added a reproducer for the bug.
>>>>> 
>>>>> Regards, peter
>>>>> 
>>>>> On 05/14/2013 07:53 AM, Peter Levart wrote:
>>>>>> Right, sb.length() should be used. I will correct that as soon as I
>>>>>> get to the keyboard.
>>>>>> 
>>>>>> Regards, Peter
>>>>>> 
>>>>>> On May 14, 2013 7:22 AM, "David Holmes" <david.holmes at oracle.com
>>>>>> <mailto:david.holmes at oracle.com>> wrote:
>>>>>> 
>>>>>>    Thanks Peter! I've filed
>>>>>> 
>>>>>>    8014477
>>>>>>    Race condition in String.contentEquals when comparing with
>>>>>>    StringBuffer
>>>>>> 
>>>>>>    On 14/05/2013 8:34 AM, Peter Levart wrote:
>>>>>> 
>>>>>>        On 05/14/2013 12:09 AM, Peter Levart wrote:
>>>>>> 
>>>>>>            I noticed a synchronization bug in String.contentEquals
>>>>>>            method. If
>>>>>>            called with a StringBuffer argument while concurrent thread is
>>>>>>            modifying the StringBuffer, the method can either throw
>>>>>>            ArrayIndexOutOfBoundsException or return true even though
>>>>>>            the content
>>>>>>            of the StringBuffer has never been the same as the String's.
>>>>>> 
>>>>>>            Here's a proposed patch:
>>>>>> 
>>>>>> http://cr.openjdk.java.net/~plevart/jdk8-tl/String.contentEquals/webrev.01/
>>>>>> <http://cr.openjdk.java.net/%7Eplevart/jdk8-tl/String.contentEquals/webrev.01/>
>>>>>> 
>>>>>>            Regards, Peter
>>>>>> 
>>>>>> 
>>>>>>        Or even better (with some code clean-up):
>>>>>> 
>>>>>> http://cr.openjdk.java.net/~plevart/jdk8-tl/String.contentEquals/webrev.02/
>>>>>> <http://cr.openjdk.java.net/%7Eplevart/jdk8-tl/String.contentEquals/webrev.02/>
>>>>>> 
>>>>>> 
>>>>>>    This part is not correct I believe:
>>>>>> 
>>>>>>    1010     private boolean
>>>>>>    nonSyncContentEquals(AbstractStringBuilder sb) {
>>>>>>    1011         char v1[] = value;
>>>>>>    1012         char v2[] = sb.getValue();
>>>>>>    1013         int n = v1.length;
>>>>>>    1014         if (n != v2.length) {
>>>>>>    1015             return false;
>>>>>>    1016         }
>>>>>> 
>>>>>>    v2 can be larger than v1 if v2 is not being fully used (ie count <
>>>>>>    length).
>>>>>> 
>>>>>>    David
>>>>>>    -----
>>>>>> 
>