scala - Akka Future Respose to a Sender -

i came across following sip:

http://docs.scala-lang.org/sips/pending/spores.html

as reading through, came across example:

def receive = {   case request(data) =>     future {       val result = transform(data)       sender ! response(result)     } } 

there description below in article:

>     capturing sender in above example problematic, since not return stable value. possible future’s body > executed @ time when actor has started processing next > request message originating different actor. > result, response message of future might sent > wrong receiver. 

i not understand line "capturing sender in above example problematic...." isn't case in each request actor (request(data)) create future block?

the creating of future block synchronous mean sender reference known @ time. execution of future block somehow scheduled happen @ later point in time.

is understanding correct?

def receive = {   case request(data) =>     future {       val result = transform(data)       sender ! response(result)     } } 

imagine line sender ! response(result) executed after 300 ms, @ same time enclosing actor handling message, let's call m. because sender def, not val, it's evaluated every time it's used. means, inside future you've got sender of m message! you've responded not sender of original message created future, other guy. mitigate problem need close on value of sender() def @ time of creation of future. compare original code this:

def receive = {   case request(data) =>     val client = sender()     future {       val result = transform(data)       client ! response(result)     } } 

you have remembered original sender, correct.

it's of utmost importance never execute methods depend on time (like sender) or change actor's state in asynchronous manner. if need change actor's state in response asynchronous computation, should send message future block.