Why are we continuing this thread when it has NOT specific to Tomcat?
Please, folks, find a Java list. There are a number of them available from
sun and from Topica.com
-----Original Message-----
From: William Kaufman [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, June 12, 2001 12:47 PM
To: '[EMAIL PROTECTED]'
Subject: RE: Java Question
> public static String getYear(String str){
> synchronized(str){
> newStr = str.substring(0,4);
> return newStr;
> }
> }
While your use of "synchronize" is correct, _this_ synchronization is not
necessary at all. java.lang.String is unmodifiable: there's nothing you can
do with it that might conflict with what another thread will do with it.
So, you never have to worry about conflicts, and you never need to
synchronize.
The answer is,
1) You need to synchronize when two threads running code might modify the
same data at the same time.
2) You need to synchronize on the exact same object around all code which
modifies a given bit of data.
3) Never synchronize on java.lang.Class objects.
The only issue about static/non-static in there is that synchronizing a
static method effectively synchronizes on the object's Class, which is a
no-no.
(You might want to read up on concurrency--see Doug Lea's "Concurrent
Programming", or his web site, http://g.oswego.edu/ .)
-- Bill K.
-----Original Message-----
From: Brandon Cruz [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, June 12, 2001 11:56 AM
To: [EMAIL PROTECTED]
Subject: RE: Java Question
So would changing something simple from...
public static String getYear(String str){
newStr = str.substring(0,4);
return newStr;
}
to...
public static String getYear(String str){
synchronized(str){
newStr = str.substring(0,4);
return newStr;
}
}
be correct if I want to avoid having incorrect results returned when
accessed by multiple threads? It compiles like that, but is that all that
is needed to synchronize something?
Brandon
-----Original Message-----
From: Luba Powell [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, June 12, 2001 1:52 PM
To: [EMAIL PROTECTED]
Subject: Re: Java Question
Actually the outcome is predictable:
monitorenter will obtain objectref on this (aload_0)
* if no other thread has locked the object
* if the object is currently locked by another thread (monitorenter
instruction)
* if the current thread already owns a lock - the lock is released when the
counter
returns to 0
.method static doSort([I)V
aload_0
monitorenter
; sensitive code
monitorexit
...
return
end method
----- Original Message -----
From: "Brandon Cruz" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, June 12, 2001 2:18 PM
Subject: Java Question
----- Original Message -----
From: "Pae Choi" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, June 12, 2001 2:41 PM
Subject: Re: Java Question
> When you access the 'synchronized' static method, it locks its class.
> so this will ensure the thread-safe access. Otherwise, the result is
> unknown.
>
>
> Pae
>
>
> > I have looked all over and can't find the answer to this simple
question.
> > If you use a static method, do you have to synchronize it in case other
> > people may access it at the same time. For example, I have a static
Utility
> > class to do date calculations. The method Utility.getMonth(String date)
> > takes in a full date string, parses it, and returns just the month
value.
> > If 5 different people all using the website attempt to use
> > Utility.getMonth(String date) at the same time for different dates, will
it
> > return the right results? If not, do I have to synchronize it or
something
> > in case multiple users attempt to access it?
> >
> > I know this is not really related to tomcat, but since I am using
tomcat,
> > and everyone else using tomcat is also a java developer, I figured this
is
> > the best place I can ask.
> >
> > Thanks for any help!!!
> >
> > Brandon
> >
>
