Subject: Is Singleton thread safe?

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Subject: Is Singleton thread safe?

Subject: Is Singleton thread safe?

2005-04-01 - By Patrick Blais

Back

Reply: 1 2 3 4 5 6 7 8 9 10 >>

It depends on the way you implement it.
You might have thread safe issues if you have per say the following class:
public class SequenceManager {
private static SequenceManager manager;
protected SequenceManager () {
super();
}
public static SequenceManager getInstance() {
if(manager == null){
manager= new SequenceManager();
return manager;
}else{
return manager;
}
is not thread safe.
The following implementation is thread safe. THe difference is when the class
loader will load the class,
it will instanciate the variable manager and this, will be done only once. You
do not need
to synchronize the method... yoou need to prevent from loading the class twice.
public class SequenceManager {
private static SequenceManager manager=new SequenceManager();
protected SequenceManager () {
super();
}
public static SequenceManager getInstance() {
return manager;
}

Sureshbabu
Koya <Sureshbabu.Koya@(protected)> wrote:
You cannot syncronize a static variable. It is always better if you modify your
variables using set/get methods. Once you syncronize your set method your
variable would be thread safe.

I saw people using synchonize blocks for servlet instance variables instead of
maintaining local variables. Since servlet is a singleton this is necessary.
Apart from this case(Singleton) I did not see people trying to synchronize
static variables.

Regards,
Suresh Koya

-- --Original Message-- --
From: An interest list for Sun Java Center J2EE Pattern Catalog [mailto
:J2EEPATTERNS-INTEREST@(protected)]On Behalf Of Julia Liu
Sent: Friday, April 01, 2005 9:47 PM
To: J2EEPATTERNS-INTEREST@(protected)
Subject: Re: Is Singleton thread safe?

Thanks for reply. Could I Synchronized static varible?

Sureshbabu Koya <Sureshbabu.Koya@(protected)> wrote: Making a singleton
thread safe is up to you. You should also think about how the performance get a
hit if you want to make a singleton threadsafe.

regards,
Suresh
-- --Original Message-- --
From: An interest list for Sun Java Center J2EE Pattern Catalog [mailto
:J2EEPATTERNS-INTEREST@(protected)]On Behalf Of Julia Liu
Sent: Friday, April 01, 2005 9:24 PM
To: J2EEPATTERNS-INTEREST@(protected)
Subject: Is Singleton thread safe?

Hi,

Is Singleton thread safe? Why?

Thanks

Julia Liu

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Julia Liu

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<DIV>It depends on the way you implement it.<BR>You might have thread safe
issues if you have per say the following class:</DIV>
<DIV>public class SequenceManager {</DIV>
<DIV>private static SequenceManager manager;<BR>protected SequenceManager () {
<BR> super();<BR>}<BR>public static SequenceManager getInstance() {</DIV>
<DIV>if(manager == null){<BR> manager= new SequenceManager();<BR>&nbsp
;return manager;<BR>}else{<BR> return manager;<BR>}</DIV>
<DIV>is not thread safe.</DIV>
<DIV>The following implementation is thread safe. THe difference is when the
class loader will load the class,</DIV>
<DIV>it will instanciate the variable manager and this, will be done only once.
You do not need</DIV>
<DIV>to synchronize the method... yoou need to prevent from loading the class
twice.</DIV>
<DIV>public class SequenceManager {</DIV>
<DIV>private static SequenceManager manager=new SequenceManager();<BR>protected
SequenceManager () {<BR> super();<BR>}</DIV>
<DIV>public static SequenceManager getInstance() {<BR> return manager;<BR>
}<BR></DIV>
<DIV> </DIV>
<DIV><B><I>Sureshbabu </I></B></DIV>
<DIV><B><I>Koya <Sureshbabu.Koya@(protected)></I></B> wrote:</DIV>
<BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER
-LEFT: #1010ff 2px solid">
<META content="MSHTML 6.00.2600.0" name=GENERATOR>
<DIV><SPAN class=062503416-01042005><FONT face=Arial color=#0000ff size=2>You
cannot syncronize a static variable. It is always better if you modify your
variables using set/get methods. Once you syncronize your set method your
variable would be thread safe.</FONT></SPAN></DIV>
<DIV><SPAN class=062503416-01042005><FONT face=Arial color=#0000ff size=2><
/FONT></SPAN> </DIV>
<DIV><SPAN class=062503416-01042005><FONT face=Arial color=#0000ff size=2>I saw
people using synchonize blocks for servlet instance variables instead
of maintaining local variables. Since servlet is a singleton this is necessary.
 Apart from this case(Singleton) I did not see people trying
to synchronize static variables.  </FONT></SPAN></DIV>
<DIV><SPAN class=062503416-01042005><FONT face=Arial color=#0000ff size=2><
/FONT></SPAN> </DIV>
<DIV><SPAN class=062503416-01042005><FONT face=Arial color=#0000ff size=2
>Regards,</FONT></SPAN></DIV>
<DIV><SPAN class=062503416-01042005><FONT face=Arial color=#0000ff size=2
>Suresh Koya</FONT></SPAN></DIV>
<DIV><SPAN class=062503416-01042005></SPAN><FONT face=Tahoma><FONT face=Arial
color=#0000ff size=2></FONT><FONT face=Arial color=#0000ff size=2></FONT><FONT
face=Arial color=#0000ff size=2></FONT><BR><FONT size=2><SPAN class=062503416
-01042005><FONT face=Arial color=#0000ff> </FONT></SPAN>-- --Original
Message-- --<BR><B>From:</B> An interest list for Sun Java Center J2EE Pattern
Catalog [mailto:J2EEPATTERNS-INTEREST@(protected)]<B>On Behalf Of </B>Julia
Liu<BR><B>Sent:</B> Friday, April 01, 2005 9:47 PM<BR><B>To:</B> J2EEPATTERNS
-INTEREST@(protected)<BR><B>Subject:</B> Re: Is Singleton thread safe?<BR><BR><
/FONT></DIV></FONT>
<BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff
2px solid">
<DIV>Thanks for reply.  Could I Synchronized static varible?<BR><BR><B><I
>Sureshbabu Koya <Sureshbabu.Koya@(protected)></I></B> wrote:
<BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER
-LEFT: #1010ff 2px solid">
<META content="MSHTML 6.00.2600.0" name=GENERATOR>
<DIV><SPAN class=405301116-01042005><FONT face=Arial color=#0000ff size=2
>Making a singleton thread safe is up to you. You should also think about how
the performance get a hit if you want to make a singleton threadsafe.</FONT><
/SPAN></DIV>
<DIV><SPAN class=405301116-01042005><FONT face=Arial color=#0000ff size=2><
/FONT></SPAN> </DIV>
<DIV><SPAN class=405301116-01042005><FONT face=Arial color=#0000ff size=2
>regards,</FONT></SPAN></DIV>
<DIV><SPAN class=405301116-01042005><FONT face=Arial color=#0000ff size=2
>Suresh</FONT></SPAN></DIV>
<BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff
2px solid">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma size=2>---
--Original Message-- --<BR><B>From:</B> An interest list for Sun Java Center
J2EE Pattern Catalog [mailto:J2EEPATTERNS-INTEREST@(protected)]<B>On Behalf Of
</B>Julia Liu<BR><B>Sent:</B> Friday, April 01, 2005 9:24 PM<BR><B>To:</B>
J2EEPATTERNS-INTEREST@(protected)<BR><B>Subject:</B> Is Singleton thread safe?
<BR><BR></FONT></DIV>
<DIV>Hi,</DIV>
<DIV> </DIV>
<DIV>Is Singleton thread safe? Why?</DIV>
<DIV> </DIV>
<DIV>Thanks<BR><BR></DIV><BR><BR>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV><FONT color=#4040ff size=3><EM><STRONG><FONT size=2>Julia  Liu 
</FONT><IMG src="http://us.i1.yimg.com/us.yimg.com/i/mesg/tsmileys2/40.gif"
NOSEND="1"></STRONG></EM></FONT></DIV></DIV></DIV></DIV></DIV></DIV></DIV></DIV
></DIV>
<P>
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<DIV>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV><FONT color=#4040ff size=3><EM><STRONG><FONT size=2>Julia  Liu 
</FONT><IMG src="http://us.i1.yimg.com/us.yimg.com/i/mesg/tsmileys2/40.gif"
NOSEND="1"></STRONG></EM></FONT></DIV></DIV></DIV></DIV></DIV></DIV></DIV></DIV
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