Problem with doPost() method executed twice in parallel

[ro...@st.com]

     Hi everybody, excuse my poor english ;)  ,  I decided to subscribe 
     because I have a serious problem blocking me and my developments since 
     one week:
     
     I work on an classical application using servlet and jsp and a 
     database (INGRES) but no EJB.
     
     Unfortunately I don't work with an IDE containing a debuuger, so I 
     must trace my code manually using System.out.println() instructions.
     
     So here is my problem :
     I call a servlet from a jsp page, the servlet is executed correctly, 
     passing in init() method (the first time), then in doPost() method.
     
     In doPost() method I make calls to others methods of others classes; 
     the output messages (issued from traces) confirm that all is correct 
     and that the methods of extern methods are well called.
     
     And suddenly, whereas the code is executing in an extern method, the 
     traces situed at the begin of doPost() method are displayed a second 
     time !!!
     It looks like if doPost() method was executed a second time IN 
     PARALLEL of the first doPost() (because the external methods issued 
     from the first doPost() continue to execute).
     
     
     I searched everywhere and I can't explain this strange behaviour, can 
     you ... ?
     
     Thanks for your answers.


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Re: Problem with doPost() method executed twice in paralle

[ro...@st.com]

     Maybe you're right but I forgot to precise some things :
     - for the moment I'm the only user testing my application so there is 
     no risk that another user creates a new thread by connecting.
     - the external classes are objects stored in session


______________________________ Reply Separator _________________________________
Subject: Re: Problem with doPost() method executed twice in paralle
Author:  tmo (tmo@ebi.ac.uk) at internet
Date:    6/7/02 3:15 PM


     
     
rosset.synlog@st.com wrote:
     
>      And suddenly, whereas the code is executing in an extern method, the 
>      traces situed at the begin of doPost() method are displayed a second 
>      time !!!
>      It looks like if doPost() method was executed a second time IN
>      PARALLEL of the first doPost() (because the external methods issued 
>      from the first doPost() continue to execute).
     
This is correct. The servlet container will create a single instance of 
the servlet class that you have written, calling the init() method at 
the time of creation. After this, each request to your servlet will map 
to a separate thread, all of which run through the same object (your 
servlet).
     
If you are accessing external objects as part of this process, you must 
ensure that either your external resources are created per-access, so 
created and referenced within the doPost() method, or that they are 
thread safe, as you have no control over when they are accessed.
     
Exactly why you are getting two invocations of your doPost() call is 
unclear, it depends on what is trying to access it, but this kind of 
behavior is common and intentional.
     
Hope that helps,
     
Tom Oinn
     
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Re: Problem with doPost() method executed twice in parallel

[Tom Oinn <tm...@ebi.ac.uk>]

rosset.synlog@st.com wrote:

>      And suddenly, whereas the code is executing in an extern method, the
>      traces situed at the begin of doPost() method are displayed a second
>      time !!!
>      It looks like if doPost() method was executed a second time IN
>      PARALLEL of the first doPost() (because the external methods issued
>      from the first doPost() continue to execute).

This is correct. The servlet container will create a single instance of
the servlet class that you have written, calling the init() method at
the time of creation. After this, each request to your servlet will map
to a separate thread, all of which run through the same object (your
servlet).

If you are accessing external objects as part of this process, you must
ensure that either your external resources are created per-access, so
created and referenced within the doPost() method, or that they are
thread safe, as you have no control over when they are accessed.

Exactly why you are getting two invocations of your doPost() call is
unclear, it depends on what is trying to access it, but this kind of
behavior is common and intentional.

Hope that helps,

Tom Oinn

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