reply inline. hopefully this makes my solution more clear.
-Michael
On 04/14/16 02:37, Mahesh Govind wrote:
Thank You .
So in case 1 , you are recommending the child to send a message to
controller when it gets a leave message .
no. i would use the same message flow as you described in your original
email. the only change i would make is instead of:
"controller will do getContext().getChild("networkdevice_IP") and get
the right FSMActor."
i would instead get the child ActorRef by consulting the map, then
immediately remove the child from the map. by 'immediately' i mean
remove the child from the map in this iteration of the actor receive
loop. since actors process their messages synchronously, there is no
chance of inconsistency.
The map(IP->actor) is maintained by controller .Controller will remove
the child from map and kill the child ?
yes.
Since controller is processing messages one by one there will not be
any inconsistency ?
yes.
Please let me know whether my understanding is right .
On Thu, Apr 14, 2016 at 5:30 AM, Michael Frank <syntaxjoc...@gmail.com
<mailto:syntaxjoc...@gmail.com>> wrote:
I can think of two solutions.
1. in your controller actor, maintain a separate mapping of
"networkdevice_IP" -> ActorRef. when you create a new child
actor, don't give it a name, let akka pick a random unique name,
then add the mapping. when routing messages to the child, instead
of using getChild(), look up the actor ref in your map. when a
child leaves, remove it from the map immediately, then stop it
asynchronously by sending the 'leave' message.
2. in your controller actor, track child actors which are leaving,
and stash messages destined to these actors until you receive
termination confirmation. you could again keep a mapping of
"networkdevice_IP" -> ActorRef, but this mapping would only hold
actors which are leaving. when you receive a message for a child,
first check if the child is leaving: if so stash() the message.
if the child is not in the leaving map, if the child exists, send
the message to it. if the child doesn't exist, create it. when a
child is leaving, put a watch on the child using context.watch(),
add the child name to the leaving map, then send the 'leave'
message to the actor. when you receive the deathwatch Terminated()
message, call unstashAll() to flush any stashed messages.
i have used the first solution many times, its quick and easy.
solution two is applicable however if you are modeling a resource
which cannot have two separate incarnations running at the same time.
-Michael
On 04/13/16 01:15, Mahesh Govind wrote:
Dear Experts ,
Could you please help me with a right design choice for the
following scenario.
*Use case * : 1000's of Network device are controlled by a
network .
* Network devices will join and leave the network by sending
*Join* and *Leave* messages respectively to the network
controller.
*Joining scenario*
* When controller get a *Join* message from a network device ,
* it will check whether an FSM actor exists for that network
device by calling getContext().getChild("networkdevice_IP").
* "networkdevice_IP" is used to identify the actor.
* if the child lookup returns null , a new FSMActor will be
spawned and join message is processed by the new FSMActor
*
Leaving scenario*
* Network device will send a *Leave* message to the controller
* controller will
do getContext().getChild("networkdevice_IP") and get the
right FSMActor.
* sends “*leave* message" to this actor.
* While processing Leave message , FSM actor will terminate
itself by calling stop() .
*Complication*
* Now there is a possibility that while the stop() is being
processed by FSMActor , a new Join may come from same network
device (networkdevice_IP).
* Since stop() is asynchronous getContext().getChild(network
device) will still return the FSMActor (networkdevice_IP) ,
but if we send message to this actor , the message will go to
DeadMessages.
*
*Design question .*
* How to handle such scenario using AKKA ? So that we will
not return a stale Actor using getContext().getChild()
* [one possiblity might be to leave this corner scenario and
let the network protocol to handle this with retransmission
.But if retransmission is not there what to do ?]
With thanks and regards
Mahesh
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