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Slap me silly, but...

Servin Park

Joined: May 10, 2002
Posts: 26
My question may seem very silly, but bare with me please. In doGet or doPost method in a servlet that doesn't implement SingThreadModel, I instanciate an object called "MyObject".
1: public void doGet(...)
2: {
3: MyObject mo = new MyObject();
4: ...
5: //using set methods in MyObject, mo is
6: //customerized for each users that call
7: //this servlet
8: process(mo);
10: }
12: private void process(MyObject mo)
13: {
14: //do something with mo
15: }
Let's say a split second later first request came in second request came in to the doGet method. By the time the first request is on the line 8, how do I know that the second request didn't changed the mo object? How do I make sure that the integrity of mo is kept? I read from somewhere that local variables and the parameters are threadsafe, but I just can't seem to understand it. Can someone explain what really happens or how it should be coded?
[ August 19, 2002: Message edited by: Servin Park ]
[ August 19, 2002: Message edited by: Servin Park ]
Pradeep bhatt
Ranch Hand

Joined: Feb 27, 2002
Posts: 8927

For every request a new object will be created in the doGet method. So the objects are thread safe

Bosun Bello
Ranch Hand

Joined: Nov 06, 2000
Posts: 1510
This servlet does NOT implement the singleThreadModel interface. So a new object wil not be created for every request. A new thread will be spawn for the same instance. If you want to guard against unfavourable results since all the threads will be sharing the same instance variables, you can either implement the SingleThreadModel interface, or synchronize access to the code in question.

So much trouble in the world -- Bob Marley
Bear Bibeault
Author and ninkuma

Joined: Jan 10, 2002
Posts: 63854

While instance variables are certainly not safe, the local variables in doGet() and doPost() are completely thread-safe.
Instance variables are created at construction-time of the servlet and only one variable per instance is created. That is why they are not safe: if multiple threads use the same object, the instance variable is shared and can get clobbered.
However, local variables within a method are created on the method's stack and are private to the invocation of that method. Thus, even if the servlet instance is shared across multiple threads, each method invocation has a private copy of its local variables and no thread-safety issues are created.
[ August 20, 2002: Message edited by: Bear Bibeault ]

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Servin Park

Joined: May 10, 2002
Posts: 26
Thank you so much for your kind suggestions/comments.
I agree. Here's the link:
subject: Slap me silly, but...
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