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From tobias.dittr...@t-online.de (Tobias Dittrich)
Subject Re: about singletons (ot)
Date Wed, 29 Jan 2003 23:16:50 GMT

Basically yes. Much less code than you normally would think needs to be
declared synchronized.  Maybe someone can post a link to a good guide to
thread synchronization - personally I only can recommend the O'Reilly Java
Thread book but that's personal taste(!)

However - as you said, synchronization implies a performance penalty as
there will be some code around the synchronized block for lock checking etc.
This is regardless of where you put the synchronized flag - a method is just
as well a code block. So make sure not to change a single large synchronized
block (such as a whole method) for a patchwork of small synchronized blocks.
You might find your thread spending the gained time (for not having to wait
for locks to become free) in synchronization management code.

Tobi



----- Original Message -----
From: "Erik Price" <eprice@ptc.com>
To: "Tomcat Users List" <tomcat-user@jakarta.apache.org>
Sent: Wednesday, January 29, 2003 9:26 PM
Subject: Re: about singletons (ot)


> So you mean that the original author (mike jackson) was saying that he
> used synchronized code blocks to apply a finer level of detail in
> specifying what is synchronized and what isn't, as opposed to just
> declaring an entire method synchronized?
>
> I understand that synchronization implies a performance penalty, but I
> wasn't sure what the advantage to using synchronized blocks over
> synchronized methods was.
>
>
> Erik
>
>
>
>
> Tobias Dittrich wrote:
> > The reason why you don't want to use synchronized methods is that a
> > synchronized block can only be executed by one thread at a time. Every
other
> > thread wanting to access this method will be blocked during this time
(well,
> > basically). So you want to try to keep the synchonized blocks as small
as
> > possible.
> >
> > Having said that I wonder weather performance is an issue in the
singleton
> > vs only-static discussion. Is there a significant difference in
execution
> > speed? After all one has to make one additional method call every time
when
> > accessing a singleton method (the getInstance() which is  synchronized,
> > too). And since we're off topic anyway: is a call to a static method
faster
> > than a "normal" one to an object (well, I mean the overhead from the
method
> > call, not the execution speed of the method body ... )?
> >
> >
> > Cheers
> > Tobi
> >
> >
> >
> > From: "Erik Price" <eprice@ptc.com>
> > To: "Tomcat Users List" <tomcat-user@jakarta.apache.org>
> > Sent: Wednesday, January 29, 2003 1:46 PM
> > Subject: Re: about singletons (ot)
> >
> >
> >
> >>
> >>Mike Jackson wrote:
> >>
> >>>The difference is that if you use a singleton there's one instance.  If
> >>>everything
> >>>is static then you only have one copy.  Usually when you use a
singleton
> >>>it's to
> >>>control access to some resource, the intent is that you use the
> >
> > singleton
> >
> >>>and some
> >>>synchronized calls (note I don't mean synchronized methods, but
> >
> > synchronized
> >
> >>>code
> >>>blocks) to control threads using that resource.
> >>
> >>Why could you not use synchronized methods?
> >>
> >>
> >>
> >>Erik


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