Re: servlet reference and thread safe

From:

Lew <lew@nowhere.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 12 Nov 2006 10:18:56 -0500

Message-ID:

<K86dnfSFq8z8psrYnZ2dnUVZ_rCdnZ2d@comcast.com>

gk wrote:

"...the instance , static variables used in a servlet reference
object are not thread safe..."

why instance variables are not thread safe ?
seperate instance will have there own copy and hence they are not
going to be mixed up in multithreading enviornment.
so, these variables are thread safe .

could you please explain ...why that statement is correct ?
this x,y cant be thraed safe ?

....

if i make synchronized setter/getter methods to access those instance
variables , will that be thread safe now ?

hiwa wrote:
Yes.

Simon Brooke wrote:

Errr... no. And if you think it is, you /really/ don't understand how a
Servlet engine works.

The servlet engine may well re-use the same instance of a servlet class to
handle multiple requests. The instance refers to its own private variables
without use of accessor methods. Since multiple threads may be using the
instance, problems might ensue.

Synchronizing access to a shared resource involves synchronizing on the
resource or one that is tied to it, as "synchronized(this)" or
"synchronized(x)". Synchronizing to the accessor methods is not reliable, as
it ignores accesses that bypass those methods.

It's better to stick with stack variables for servlet action.

- Lew