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Subject: Re: Groovy category throwing MissingMethodException and
 MissingPropertyException when using multiple threads
From: Keith Suderman <suderman@anc.org>
In-Reply-To: <563278FA.8070404@gmx.org>
Date: Thu, 29 Oct 2015 23:43:33 -0400
Cc: dev@groovy.incubator.apache.org
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Message-Id: <A6712BC9-36F7-47C7-BA5F-2A22D24C4A2D@anc.org>
References: 
 <CAJ4jX6jWc4BbotTB3jkKyw-ycgFm6bCqWqNQoHGAaxny8pDGqA@mail.gmail.com>
 <56311C00.9020702@gmx.net>
 <1BCD07F2-703A-4EA8-B5C9-FBC5B99DC116@cs.vassar.edu>
 <563278FA.8070404@gmx.org>
To: users@groovy.incubator.apache.org

Hi Jochen,

I am not positive this is the cause of the problem here, but it sets off =
alarm bells in my head.  Consider lines 75 and 76:

          atomicCategoryUsageCounter.incrementAndGet();
          categoriesInUse =3D atomicCategoryUsageCounter.get();

Line 75 does an incrementAndGet() but ignores the result.  The value is =
then obtained again on the next line with another call to get() leaving =
a tiny window for another thread to increment/decrement the counter.  =
That is what I meant by =E2=80=9Cnon-atomic usage=E2=80=9D. This should =
be:

          categoriesInUse =3D =
atomicCategoryUsageCounter.incrementAndGet();

The same thing happens in the endScope() method (lines 99-100); the code =
calls getAndDecrement(), ignores the result, and then calls the get() =
method again on the next line, leaving another tiny window for another =
thread to change the value.=20

I haven=E2=80=99t had a chance to figure out why Groovy won=E2=80=99t =
build on my system so I can=E2=80=99t submit a PR for this.

Cheers,
Keith


> On Oct 29, 2015, at 3:52 PM, Jochen Theodorou <blackdrag@gmx.org> =
wrote:
>=20
> On 29.10.2015 11:48, Suderman Keith wrote:
>> There are (at least) two race conditions in =
GroovyCategorySupport.java
>> that would explain the intermittent and hard to reproduce bugs.
>>=20
>> I was hoping to submit this as my first official pull request to the
>> Groovy project, but gradle has different ideas=E2=80=A6
>>=20
>> However, the offending code is in on lines 75-76 and 99-100 where
>> atomicCategoryUsageCounter is used non-atomically. If no one beats me =
to
>> it I will submit a PR once I puzzle out why ./gradlew test is failing
>> for me.
>=20
> Can you explain the non-atomic usage and why it leads to a problem =
here?
>=20
> bye blackdrag

------------------------------
Research Associate
Department of Computer Science
Vassar College
Poughkeepsie, NY