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Posted to users@tomcat.apache.org by Christopher Schultz <ch...@christopherschultz.net> on 2009/06/15 18:32:24 UTC
Re: [OT] using static helper classes within servlets
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David,
On 6/14/2009 5:43 PM, David Blevins wrote:
> Regardless of that choice we
> will still handle sychronization of instantiation, so
> double-check-locking or other things will not be necessary.
NB: DCL does not work in Java. Period.
http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
There are cases where you /can/ make it work, but let's face it: most
programmers simple cannot be trusted to do it properly. Also, the
techniques are very sensitive to JVM level, etc. so you'd need to have a
different implementation depending on which JVM you were running. Yuk.
- -chris
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Re: [OT] using static helper classes within servlets
Posted by David Blevins <da...@visi.com>.
On Jun 15, 2009, at 9:32 AM, Christopher Schultz wrote:
> On 6/14/2009 5:43 PM, David Blevins wrote:
>> Regardless of that choice we
>> will still handle sychronization of instantiation, so
>> double-check-locking or other things will not be necessary.
>
> NB: DCL does not work in Java. Period.
>
> http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
>
> There are cases where you /can/ make it work, but let's face it: most
> programmers simple cannot be trusted to do it properly. Also, the
> techniques are very sensitive to JVM level, etc. so you'd need to
> have a
> different implementation depending on which JVM you were running. Yuk.
Chris, I was referring to the EJB 3.1 Singleton bean type which would
free him up from having to write that complicated code you mention.
-David
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RE: [OT] using static helper classes within servlets
Posted by "Caldarale, Charles R" <Ch...@unisys.com>.
> From: Christopher Schultz [mailto:chris@christopherschultz.net]
> Subject: Re: [OT] using static helper classes within servlets
>
> NB: DCL does not work in Java. Period.
While that statement was true for 1.4 and prior JVMs, 1.5 actually made DCL work.
> http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
Note that the majority of the above was written prior to the development of JSR 133, let alone its implementation; my reading of JSR 133 indicates that the volatile keyword is no longer required, due to the requirement of flushing any internally cached values at the entrance to a synchronized block.
- Chuck
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Re: [OT] using static helper classes within servlets
Posted by Christopher Schultz <ch...@christopherschultz.net>.
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Tim,
On 6/15/2009 12:43 PM, Tim Funk wrote:
> correction: The double checked idiom was "fixed" in java5. The variable
> which is checked needs to be declared as volatile. The link states that
> at the bottom.
...which is why I said:
>> There are cases where you /can/ make it work, but let's face it: most
>> programmers simple cannot be trusted to do it properly. Also, the
>> techniques are very sensitive to JVM level, etc. so you'd need to have a
>> different implementation depending on which JVM you were running. Yuk.
- -chris
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Re: [OT] using static helper classes within servlets
Posted by Tim Funk <fu...@apache.org>.
correction: The double checked idiom was "fixed" in java5. The variable
which is checked needs to be declared as volatile. The link states that
at the bottom.
-Tim
Christopher Schultz wrote:
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> Hash: SHA1
>
> David,
>
> On 6/14/2009 5:43 PM, David Blevins wrote:
>
>> Regardless of that choice we
>> will still handle sychronization of instantiation, so
>> double-check-locking or other things will not be necessary.
>>
>
> NB: DCL does not work in Java. Period.
>
> http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
>
> There are cases where you /can/ make it work, but let's face it: most
> programmers simple cannot be trusted to do it properly. Also, the
> techniques are very sensitive to JVM level, etc. so you'd need to have a
> different implementation depending on which JVM you were running. Yuk.
>
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