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From "Thilina Gunarathne" <cset...@gmail.com>
Subject Re: [axis2] Improvements to Service life cycle in handling - setOperationContext not thread-safe??!!
Date Tue, 10 Oct 2006 17:13:08 GMT
Ok... Here's my suggestion.. Let's create new service objects per invocation..

AFAIK two things happen when we deploy a service in application scope.
One is that Axis2 will maintain a single service context throughout
the life of the service.. Other thing is Axis2 maintains one service
class object throughout the life of the service, serving for all the
requests..

Maintaining of the service context is really important and useful..
Users can use it to store whatever the state data that needs to shared
throughout the life of the service. IIRC this is one of the use cases
we came up with for the Axis2 context hierarchy- to make the engine
stateless..

On the other hand, i don't see any reason for maintaining a single
service object throughout the life of the service. IMO anybody can use
the ServiceContext to store whatever the state data needed to be
shared across the life of the service...Are there any special cases
where we can't do that.. If there aren't any reasons my suggestion is
to  create the service object per invocation.

Also a user who uses the application scope might most probably be
working in the messagereceiver(MR) level, since MR is known to be the
ultimate message recipient in Axis2. One possible example is a BPEL
engine.. In that case the concept of one service object for the life
time of the service invalidates.. AFAIKS AXIS2-1133 is another
implication of this design...

Thanks,
Thilina

On 10/10/06, Sanjiva Weerawarana <sanjiva@opensource.lk> wrote:
> Other choices?
>
> The approach we used back in ApacheSOAP was to tell the user to add an
> additional first parameter to their methods if they wanted the
> context .. so the signature would have an additional param and that'd
> tell us to do the right thing. Very thread safe.
>
> Need to avoid reflection - but can be done by a codegen flag. For RPC
> case its reflective anyway so its not a big deal.
>
> Sanjiva.
>
> On Tue, 2006-10-10 at 09:40 -0400, Davanum Srinivas wrote:
> > Sanjiva,
> >
> > We had terrible problems with TLS in Axis1...let me recollect my
> > thougts and post.
> >
> > -- dims
> >
> > On 10/10/06, Sanjiva Weerawarana <sanjiva@opensource.lk> wrote:
> > > I think I agree with you. How about we drop setOperationContext() and
> > > introduce Axis1-style MessageContext.getCurrentContext() which returns
> > > it for this thread? Have to be careful to put it in TLS and take it off!
> > >
> > > We must be careful to tell users that instance variables are not
> > > supported; you have to use MessageContext properties to store state (or
> > > wherever else).
> > >
> > > Sanjiva.
> > >
> > > On Sun, 2006-09-24 at 14:12 +0200, Christopher Sahnwaldt wrote:
> > > > Entered as http://issues.apache.org/jira/browse/AXIS2-1224 .
> > > > I set the priority to blocker as David suggested.
> > > >
> > > > IMHO it's probably best to drop the method. Many users will use it in
an
> > > > intuitive but wrong way. The only way to store the data it provides is
an
> > > > instance variable, and telling users to either use only request scope
or use
> > > > a ThreadLocal to store the data does not seem to be compatible with the
> > > > rule of least surprise. Something like MessageContext.getCurrentContext()
> > > > in Axis 1 might be better.
> > > >
> > > > Bye,
> > > > Christopher.
> > > >
> > > > Davanum Srinivas wrote:
> > > > > Chris,
> > > > >
> > > > > Can you please raise a new issue in JIRA?
> > > > >
> > > > > thanks,
> > > > > dims
> > > > >
> > > > > On 9/23/06, Christopher Sahnwaldt <chrisahn@gmx.net> wrote:
> > > > >> Something worries me:
> > > > >>
> > > > >> > setOperationContext(OperationContext) - per call.  The messageContext
> > > > >> > can be obtained to gain per call instance information.
> > > > >>
> > > > >> That doesn't seem to be thread-safe, does it? If I understand
this
> > > > >> correctly, one service object is created per application (if
the
> > > > >> service has application scope). When a request comes in, Axis
calls
> > > > >> the setOperationContext method, and the service object may store
the
> > > > >> OperationContext or the MessageContext. Then Axis calls the actual
> > > > >> service method, in which the service code can access the stored
> > > > >> OperationContext or MessageContext. But what if two requests
come
> > > > >> in almost simultaneously? The following sequence of method calls
> > > > >> may occur:
> > > > >>
> > > > >> - Axis calls setOperationContext with context for request A,
the
> > > > >>   service object stores the context in an instance field.
> > > > >> - Axis calls setOperationContext with context for request B,
the same
> > > > >>   service object stores the context in the same instance field
and
> > > > >>   thus *overwrites* the context for call A.
> > > > >> - Axis calls the service method with the input parameters for
request A.
> > > > >> - The service method processes the call, using data from the
stored
> > > > >>   context, and thus *mixes the input parameters for call A with
the
> > > > >>   context data for call B*. Anything can happen...
> > > > >> - Finally, Axis calls the service method with the input parameters
> > > > >>   for call B, the service method processes the call, using data
from
> > > > >>   the stored context, and thus correctly uses the input parameters
> > > > >>   for call B with the context data for call B. Probably ok, unless
> > > > >>   the service method updated the context in some way during the
call
> > > > >>   for request A.
> > > > >>
> > > > >> But I hope I'm wrong or misunderstood or forgot something...
;-)
> > > > >>
> > > > >> Axis 1 avoided this problem by MessageContext.getCurrentContext(),
> > > > >> which gives access to the MessageContext *for the current thread*
> > > > >> from within any service method, without the need for a
> > > > >> setMessageContext (or setOperationContext) method on the service
> > > > >> object.
> > > > >>
> > > > >> Bye,
> > > > >> Christopher.
> > > > >>
> > > > >>
> > > > >> Tony Dean wrote:
> > > > >>
> > > > >> > Can we fully document the logical semantics behind each
method?
> > > > >> >
> > > > >> > init(ServiceContext) - To me this use to mean application
init.
> > > > >> Now it means session init.  However, when running
> > > > >> scope="Application", it is analogous to application init since
you
> > > > >> will only have one session;  but, still probably not appropriate
to
> > > > >> think in those terms.
> > > > >> >
> > > > >> > How should an application use this method?  A session use-case
> > > > >> would be nice.
> > > > >> >
> > > > >> > destroy(ServiceContext) - inverse of init()
> > > > >> > Use-case?
> > > > >> >
> > > > >> > setOperationContext(OperationContext) - per call.  The
> > > > >> messageContext can be obtained to gain per call instance information.
> > > > >> >
> > > > >> > StartUp() - one time initialization... DB connections etc...
> > > > >> > Shutdown() - inverse of StartUp()
> > > > >> >
> > > > >> > Any more insight or corrections to pattern usage would be
grateful...
> > > > >> >
> > > > >> > Thanks.
> > > > >> >
> > > > >> > -----Original Message-----
> > > > >> > From: robert lazarski [mailto:robertlazarski@gmail.com]
> > > > >> > Sent: Friday, September 15, 2006 8:49 AM
> > > > >> > To: axis-dev@ws.apache.org
> > > > >> > Subject: Re: Improvements to Service life cycle in handling
> > > > >> >
> > > > >> > That makes sense to me. I've been using startUp() and it
doesn't
> > > > >> really fit with the other methods of the interface in its current
> > > > >> form. +1 for 1.1 since its interface changes and it'd be better
to do
> > > > >> it now.
> > > > >> >
> > > > >> > One question: Currently you need this in services.xml to
get
> > > > >> startUp() to invoke:
> > > > >> >
> > > > >> > <parameter name="load-on-startup" locked="false">true</parameter>
> > > > >> >
> > > > >> > I plan on testing this when its ready ... since the spring
tutorial
> > > > >> depends on it ... so I thought I'd ask if the services.xml param
will
> > > > >> remain the same.
> > > > >> >
> > > > >> > Thanks,
> > > > >> > Robert
> > > > >> >
> > > > >> > On 9/14/06, Deepal Jayasinghe <deepal@opensource.lk>
wrote:
> > > > >> >
> > > > >> >> Hi All;
> > > > >> >>
> > > > >> >> Currently we have an interface called Service and which
has few
> > > > >> >> methods that are used to manage session (or else user
can add those
> > > > >> >> method into service impl class w.o implementing the
interface). And
> > > > >> >> that interface has the following methods ;
> > > > >> >>
> > > > >> >> - startUp
> > > > >> >> - init
> > > > >> >> - setOperationContext
> > > > >> >> - destroy
> > > > >> >>
> > > > >> >> Three of them are for managing service life cycle ;
> > > > >> >> - init - will be called when the session start
> > > > >> >> - setOperationContext - immediately before calling actual
java method
> > > > >> >> - destroy - will be call when the session finishes
> > > > >> >>
> > > > >> >> Remember all those method work if and only if you use
Axis2 default
> > > > >> >> message receiver or you code gen.
> > > > >> >>
> > > > >> >> The method startUp is not session related method , which
is useful
> > > > >> >> when you want to initialize database connections , create
thread etc
> > > > >> >> ... at the time when you deploy the service. In the
mean time
> > > > >> >> interface name Service is bit confusing to me AFAIK
it should be
> > > > >> >> ServiceLifeCycle. And having method like startUp in
that interface
> > > > >> confuses the users.
> > > > >> >>
> > > > >> >> So how about the following changes ;
> > > > >> >> - Rename Service interface into ServiceLifeCycle
> > > > >> >> - Then remove startUp method from that interface.
> > > > >> >>
> > > > >> >> There should be a some other interface (like Module
interface) and
> > > > >> >> which should be optional as well , to have the method
startUp. If
> > > > >> >> someone want to open DB connection or anything at the
time of service
> > > > >> >> deploying , then he need to implement that interface
(and for me
> > > > >> which
> > > > >> >> is identical to Module interface). So with this change
service
> > > > >> element
> > > > >> >> inside the services.xml will be change to following
> > > > >> >>
> > > > >> >> <service name="foo" *class="implementation class
of the interface "*>
> > > > >> >> <parameter name="ServiceClass">ServiceClass</parameter>
> > > > >> >> </service>
> > > > >> >>
> > > > >> >> Here the class attribute is optional , so if someone
want to have
> > > > >> >> loadonStartup feature then he need to implement the
Service interface
> > > > >> >> (new one) and put the impl name as the class attribute.
This is very
> > > > >> >> useful if your service implementation class is not java
(if you are
> > > > >> >> writing a groovy serice).
> > > > >> >>
> > > > >> >> So new Service interface will be look like follows;
public interface
> > > > >> >> Service{ //will be called when service is deployed public
void
> > > > >> >> startUp(ConfigurationContext configctx, AxisService
service); //will
> > > > >> >> be called when Axis2 server showdown or when service
removed from the
> > > > >> >> system public void shutDown(ConfigurationContext configctx,
> > > > >> >> AxisService service); }
> > > > >> >>
> > > > >> >> And ServiceLifeCycle interface will look like below;
> > > > >> >>
> > > > >> >> public interface ServiceLifeCycle {
> > > > >> >> public void init(ServiceContext sc);
> > > > >> >> public void setOperationContext(OperationContext operationContext);
> > > > >> >> void destroy(ServiceContext sc); }
> > > > >> >>
> > > > >> >>
> > > > >> >> I am +1 on doing this for Axis2 1.1 :)
> > > > >> >>
> > > > >> >> Suggestions ........
> > > > >> >>
> > > > >> >> Thanks
> > > > >> >> Deepal
> > > > >> >>
> > > > >> >>
> > > > >> >>
> > > > >> >> ---------------------------------------------------------------------
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> > > > >> >>
> > > > >> >>
> > > > >> >>
> > > > >> >
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> > > > >> >
> > > > >> >
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> > > > >> >
> > > > >>
> > > > >>
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> > > > >>
> > > > >>
> > > > >
> > > > >
> > > >
> > > >
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> > > >
> > >
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> >
> >
>
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-- 
http://webservices.apache.org/~thilina/
http://thilinag.blogspot.com/

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