hi all!
> -----Original Message-----
> From: Luc Vanlerberghe [mailto:[EMAIL PROTECTED]]
> Sent: Friday, January 26, 2001 6:14 PM
> To: [EMAIL PROTECTED]
> Subject: Re: Thread-safety
>
>
> > Does this mean that the following code would be thread safe?
> NO, it's not!
sorry to intervene here. i think you are wrong. look at it again:
> [...]
> > Does this mean that the following code would be thread safe?
> >
> > if (_jspx_inited == false) {
> > synchronized (this) {
> > if (_jspx_inited == false) {
> > synchronized(new Object()) {_jspx_init();}
> > _jspx_inited = true;
> > }
> > }
> > }
this double check is a usual technique to improve performance. the inner
check is necessary for proper operation. the outer check improves
performance since it does not require a lock on the object to be acquired
which is relatively costly.
and, btw. why did they not code this:
if ( ! _jspx_inited ) {
synchronized (this) {
if ( ! _jspx_inited ) {
// other initialization stuff
_jspx_inited = true;
}
}
}
i think it is quite superfluous to compare a boolean with true or false
(apart from the fact that in other programming languages this might even be
dangerous, just think of C...)
regards
robert
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