Re: Re[4]: java.util.Date
Apologies if I'm misinterpreting, but I think Antoni's concern is that the
SimpleDateFormat's parse and format methods are not thread-safe. The creation
of the converters and their registration can obviously be accomplished in a
thread-safe manner, but if multiple threads call into parse and/or format at
the same time, this will cause a problem. If that's not what Antoni was
saying...it's still a problem ;-). Shouldn't you code a Converter's convert
method with the same approach to thread-safety as an Action's execute/perform
method? If your Converter maintains a SimpleDateFormat instance field that it
uses to either format or parse, it's not thread safe.
Quoting Rick Reumann [EMAIL PROTECTED]:
On Wednesday, November 6, 2002, 4:05:45 PM, Antoni wrote:
AR Hi, I don't speak english very very well, so this is a bit
AR difficult for me to explain, but I'll try ;-)
No problem. Most American's don't speak English very well
(including myself I'm sure:)
AR I have'nt looked at the beanutils Converter registration, do you have to
AR register a class or an instance?
It registers an instance one time in the static block at the top
of the action:
static {
DateBeanUtilsConverter dateConverter = new
DateBeanUtilsConverter();
dateConverter.setFormatPattern( MMdd );
StringBeanUtilsConverterDate myStringConverter = new
StringBeanUtilsConverterDate();
myStringConverter.setFormatPattern( MMdd );
ConvertUtils.register( dateConverter, java.util.Date.class );
ConvertUtils.register( myStringConverter, String.class );
}
AR The problem here is that if there is only one instance of your class, and
AR setFormatPattern is only called once, then if there are two request that
AR require the use of your class a the same time, served by different
threads,
AR the parse method in your instance of SimpleDateFormat might be called
AR concurrently, so (as it isn't thread save) it might fail.
I'm not sure how this would happen as Eddie have both pointed out
that the static block will only get called one time regardless of
how many instances are created (at least on a single JVM I'm
pretty sure that's the case). (On top of that I'm pretty sure on
one JVM user's all share one servlet instance unless you maybe use
that SingleThreadModel which I think hands them out from a pool.
Moot point though I think if I do the stuff in the static block.
But I could be wrong).
--
Rick
mailto:maillist;reumann.net
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Kris Schneider mailto:kris;dotech.com
D.O.Tech http://www.dotech.com/
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Re: Re[4]: java.util.Date
A Dimecres 06 Novembre 2002 22:19, Rick Reumann va escriure:
On Wednesday, November 6, 2002, 4:05:45 PM, Antoni wrote:
AR Hi, I don't speak english very very well, so this is a bit
AR difficult for me to explain, but I'll try ;-)
No problem. Most American's don't speak English very well
(including myself I'm sure:)
:)
AR I have'nt looked at the beanutils Converter registration, do you have
to AR register a class or an instance?
It registers an instance one time in the static block at the top
of the action:
static {
DateBeanUtilsConverter dateConverter = new
DateBeanUtilsConverter(); dateConverter.setFormatPattern( MMdd );
StringBeanUtilsConverterDate myStringConverter = new
StringBeanUtilsConverterDate(); myStringConverter.setFormatPattern(
MMdd );
ConvertUtils.register( dateConverter, java.util.Date.class );
ConvertUtils.register( myStringConverter, String.class );
}
AR The problem here is that if there is only one instance of your class,
and AR setFormatPattern is only called once, then if there are two request
that AR require the use of your class a the same time, served by different
threads, AR the parse method in your instance of SimpleDateFormat might be
called AR concurrently, so (as it isn't thread save) it might fail.
I'm not sure how this would happen as Eddie have both pointed out
that the static block will only get called one time regardless of
how many instances are created (at least on a single JVM I'm
pretty sure that's the case). (On top of that I'm pretty sure on
one JVM user's all share one servlet instance unless you maybe use
that SingleThreadModel which I think hands them out from a pool.
Moot point though I think if I do the stuff in the static block.
But I could be wrong).
The problem is not in the static code, the problem is reusing the same
instance of SimpleDateFormat
Your initial aproach is fine. But let see what could happen if you move the
SimpleDateFormat creation to the setFormatPattern method:
- when the class loader loads your Action the static bloc is executed:
1- an instance of your converter is created
2- the setFormatPattern is called and an instance off SimpleDateFormat is
created.
3- the converter instance is registered
- there are 2 request at the same time that target an action that uses
BeanUtils.copyProperties with a bean that has a Date.
- the 2 request are served by to differents threads A and B
4- thread A begins the execution of the Action.execute,
5- thread A begins the execution of BeanUtils.copyProperties
6- thread A begins the execution of DateBeanUtilsConverter.convert
7- thread A begins the execution of SimpleDateFormat.parse
8- thread A is stopped and thread B begins the execution
9- thread B begins the execution of the Action.execute,
10- thread B begins the execution of BeanUtils.copyProperties
11- thread B begins the execution of DateBeanUtilsConverter.convert
12- thread B begins the execution of SimpleDateFormat.parse
13- thread B is stopped and thread A begins the execution
14 - thread A continues the execution of SimpleDateFormat.parse , but a
internal attribute of SimpleDateFormat where modified and it fails.
The problem is that during execution of SimpleDateFormat.parse some private
fields of SimpleDateFormat are modified.
You can take a look at
http://developer.java.sun.com/developer/bugParade/bugs/4228335.html
for details on the format classes not being thread-save issue
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Re: Re[4]: java.util.Date
Hi,
A Dimecres 06 Novembre 2002 22:31, Kris Schneider va escriure:
Apologies if I'm misinterpreting, but I think Antoni's concern is that the
SimpleDateFormat's parse and format methods are not thread-safe. The
creation of the converters and their registration can obviously be
accomplished in a thread-safe manner, but if multiple threads call into
parse and/or format at the same time, this will cause a problem. If that's
not what Antoni was saying...it's still a problem ;-). Shouldn't you code a
Converter's convert method with the same approach to thread-safety as an
Action's execute/perform method? If your Converter maintains a
SimpleDateFormat instance field that it uses to either format or parse,
it's not thread safe.
That's exactly what I was trying to say!
Thanks for the clarification
Quoting Rick Reumann [EMAIL PROTECTED]:
On Wednesday, November 6, 2002, 4:05:45 PM, Antoni wrote:
AR Hi, I don't speak english very very well, so this is a bit
AR difficult for me to explain, but I'll try ;-)
No problem. Most American's don't speak English very well
(including myself I'm sure:)
AR I have'nt looked at the beanutils Converter registration, do you have
to
AR register a class or an instance?
It registers an instance one time in the static block at the top
of the action:
static {
DateBeanUtilsConverter dateConverter = new
DateBeanUtilsConverter();
dateConverter.setFormatPattern( MMdd );
StringBeanUtilsConverterDate myStringConverter = new
StringBeanUtilsConverterDate();
myStringConverter.setFormatPattern( MMdd );
ConvertUtils.register( dateConverter, java.util.Date.class );
ConvertUtils.register( myStringConverter, String.class );
}
AR The problem here is that if there is only one instance of your class,
and
AR setFormatPattern is only called once, then if there are two request
that
AR require the use of your class a the same time, served by different
threads,
AR the parse method in your instance of SimpleDateFormat might be called
AR concurrently, so (as it isn't thread save) it might fail.
I'm not sure how this would happen as Eddie have both pointed out
that the static block will only get called one time regardless of
how many instances are created (at least on a single JVM I'm
pretty sure that's the case). (On top of that I'm pretty sure on
one JVM user's all share one servlet instance unless you maybe use
that SingleThreadModel which I think hands them out from a pool.
Moot point though I think if I do the stuff in the static block.
But I could be wrong).
--
Rick
mailto:maillist;reumann.net
--
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