RE: multiple init() calls
Hi, -Original Message- From: Serge A. Redchuk [mailto:[EMAIL PROTECTED]] Sent: Thursday, January 31, 2002 10:34 AM To: [EMAIL PROTECTED] Subject: multiple init() calls Hi All ! I've encountered a problem with creating threads of init servlet. Forgive me if I'm wrong. As I think, catalina must call init() method of init servlet _once_. And then just must make only copies of init servlet instance for new user requests. But I've encountered that the init() method called again and again ! At every creation of new action router. Does your servlet implement SingleThreadModel? If so you got what you wanted, AFAIK. It is not the thing that I need !!! Platform: pc Os: linux JDK: IBM Java web.xml: ... !-- Standard Action Servlet Configuration (with debugging) -- servlet servlet-nameaction/servlet-name servlet-class.ActionRouterServlet/servlet-class init-param param-nameapplication/param-name param-valueApplicationResources/param-value /init-param init-param ... Anton -- To unsubscribe: mailto:[EMAIL PROTECTED] For additional commands: mailto:[EMAIL PROTECTED] Troubles with the list: mailto:[EMAIL PROTECTED]
Re: multiple init() calls
hi i think there may be a misunderstanding (or i misunderstood your message ?!) the servlet must create _only_ one instance of each servlet class per web application then this instance must receive _one_ message init() at this point user request may be served for each user request, a thread is started and executes the service(...) method on the _shared_ instance the singleThreadModel only tells the servlet engine not to serve several request simultaneously this is the behaviour required by the J2EE specs as for your problem, i'm doing servlet for about 2 years now and i never saw that kind of behaviour... may be a look at your code would help... have fun! David -Original Message- From: Serge A. Redchuk [mailto:[EMAIL PROTECTED]] Hi All ! I've encountered a problem with creating threads of init servlet. Forgive me if I'm wrong. As I think, catalina must call init() method of init servlet _once_. And then just must make only copies of init servlet instance for new user requests. But I've encountered that the init() method called again and again ! At every creation of new action router. Does your servlet implement SingleThreadModel? If so you got what you wanted, AFAIK. It is not the thing that I need !!! Platform: pc Os: linux JDK: IBM Java web.xml: ... !-- Standard Action Servlet Configuration (with debugging) -- servlet servlet-nameaction/servlet-name servlet-class.ActionRouterServlet/servlet-class init-param param-nameapplication/param-name param-valueApplicationResources/param-value /init-param init-param ... Anton -- To unsubscribe: mailto:[EMAIL PROTECTED] For additional commands: mailto:[EMAIL PROTECTED] Troubles with the list: mailto:[EMAIL PROTECTED] -- To unsubscribe: mailto:[EMAIL PROTECTED] For additional commands: mailto:[EMAIL PROTECTED] Troubles with the list: mailto:[EMAIL PROTECTED]
RE: multiple init() calls
Hi,
-Original Message-
From: David Rault [mailto:[EMAIL PROTECTED]]
Sent: Thursday, January 31, 2002 11:36 AM
To: Tomcat Users List
Subject: Re: multiple init() calls
hi
i think there may be a misunderstanding (or i misunderstood your
message ?!)
the servlet must create _only_ one instance of each servlet class per web
application
I believe there is no such MUST in spec.
then this instance must receive _one_ message init()
at this point user request may be served
for each user request, a thread is started and executes the service(...)
method on the
_shared_ instance
the singleThreadModel only tells the servlet engine not to serve several
request simultaneously
this is the behaviour required by the J2EE specs
as for your problem, i'm doing servlet for about 2 years now and
i never saw
that kind of
behaviour... may be a look at your code would help...
So, lets turn to spec (Servlet 2.3)
cite
SRV.14.2.20 SingleThreadModel
public interface SingleThreadModel
Ensures that servlets handle only one request at a time. This interface has no
methods.
If a servlet implements this interface, you are guaranteed that no two threads will
execute concurrently in the servlet?s service method. The servlet container can
make this guarantee by synchronizing access to a single instance of the servlet, or
by maintaining a pool of servlet instances and dispatching each new request to a
free servlet.
This interface does not prevent synchronization problems that result from servlets
accessing shared resources such as static class variables or classes outside the
scope of the servlet.
/cite
I believe TC (at least 4.0.2b2) chose the second variant. The pool of instances.
So any instance have to be properly initialized.
just an example
package webtests;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
public class SingleThread extends HttpServlet implements SingleThreadModel {
private static int cnt = 0;
private static final String CONTENT_TYPE = text/html; charset=windows-1251;
/**Initialize global variables*/
public void init() throws ServletException {
System.err.println(init at + Thread.currentThread().toString());
System.err.println(Counter: + (++cnt));
System.err.println(Instance: + this.toString());
}
/**Process the HTTP Get request*/
public void doGet(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException {
response.setContentType(CONTENT_TYPE);
PrintWriter out = response.getWriter();
out.println(html);
out.println(headtitleSingleThread/title/head);
out.println(body);
out.println(pThe servlet has received a GET. This is the reply./p);
out.println(/body/html);
}
}
and TC console:
init at Thread[HttpProcessor[8080][0],5,main]
Counter: 1
Instance: webtests.SingleThread@19dc16
init at Thread[HttpProcessor[8080][0],5,main]
Counter: 2
Instance: webtests.SingleThread@405d3b
BTW, I'm not sure but it looks like TC3.2 creates only one instance.
Sorry, cant use attachments due to some security restrictions.
:E
have fun!
David
Anton.
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RE: multiple init() calls
See intermixed below.
On Thu, 31 Jan 2002, Anton Brazhnyk wrote:
Date: Thu, 31 Jan 2002 12:20:16 +0200
From: Anton Brazhnyk [EMAIL PROTECTED]
Reply-To: Tomcat Users List [EMAIL PROTECTED]
To: Tomcat Users List [EMAIL PROTECTED]
Subject: RE: multiple init() calls
Hi,
-Original Message-
From: David Rault [mailto:[EMAIL PROTECTED]]
Sent: Thursday, January 31, 2002 11:36 AM
To: Tomcat Users List
Subject: Re: multiple init() calls
hi
i think there may be a misunderstanding (or i misunderstood your
message ?!)
the servlet must create _only_ one instance of each servlet class per web
application
I believe there is no such MUST in spec.
If your servlet does not implement SingleThreadModel, there is indeed such
a must requirement, in Section 2.2 of the Servlet 2.3 spec:
For a servlet not hosted in a distributed
environment, the servlet container must use
only one instance per servlet declaration.
The very next sentence covers SingleThreadModel semantics:
However, for a servlet implementing the
SingleThreadModel interface, the servlet
container may instantitate multiple instances
to handle a heavy request load and serialize
requests to a particular instance.
(Personal aside -- SingleThreadModel should be avoided, because it implies
promises about thread safety that get beginners into all sorts of
trouble.)
Note that both sentences above refer to a servlet declaration, which is
a single instance of a servlet element in your web.xml file. It's legal
to use the same servlet class in more than one servlet declaration
(perhaps with different initialization parameters) if you wish -- but you
will get a separate servlet instance for each declaration.
Tomcat also supports the non-standard invoker mechanism to execute
servlets that have not been defined in web.xml, by using context-relative
paths like /servlet/foo. For the purposes of the above discussion, each
unique value of /foo creates a unique servlet declaration on the fly,
which is initialized once (if non-STM) or potentially multiple times (if
STM) and then reused for the remainder of the lifetime of this webapp.
then this instance must receive _one_ message init()
at this point user request may be served
for each user request, a thread is started and executes the service(...)
method on the
_shared_ instance
the singleThreadModel only tells the servlet engine not to serve several
request simultaneously
this is the behaviour required by the J2EE specs
as for your problem, i'm doing servlet for about 2 years now and
i never saw
that kind of
behaviour... may be a look at your code would help...
So, lets turn to spec (Servlet 2.3)
cite
SRV.14.2.20 SingleThreadModel
public interface SingleThreadModel
Ensures that servlets handle only one request at a time. This interface has no
methods.
If a servlet implements this interface, you are guaranteed that no two threads will
execute concurrently in the servlet?s service method. The servlet container can
make this guarantee by synchronizing access to a single instance of the servlet, or
by maintaining a pool of servlet instances and dispatching each new request to a
free servlet.
This interface does not prevent synchronization problems that result from servlets
accessing shared resources such as static class variables or classes outside the
scope of the servlet.
/cite
I believe TC (at least 4.0.2b2) chose the second variant. The pool of instances.
So any instance have to be properly initialized.
The ability to pool SingleThreadModel (STM) instances was recently added
to Tomcat 4.0. Previously, the instance pool was limited to one. Now,
the default maximum number of instances is 20.
just an example
package webtests;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
public class SingleThread extends HttpServlet implements SingleThreadModel {
private static int cnt = 0;
private static final String CONTENT_TYPE = text/html; charset=windows-1251;
/**Initialize global variables*/
public void init() throws ServletException {
System.err.println(init at + Thread.currentThread().toString());
System.err.println(Counter: + (++cnt));
System.err.println(Instance: + this.toString());
}
/**Process the HTTP Get request*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType(CONTENT_TYPE);
PrintWriter out = response.getWriter();
out.println(html);
out.println(headtitleSingleThread/title/head);
out.println(body);
out.println(pThe servlet has received a GET. This is the reply./p);
out.println(/body/html);
}
}
and TC console:
init at Thread[HttpProcessor[8080][0],5,main]
Counter: 1
Instance: webtests.SingleThread@19dc16
init
