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Rendezvous: Difference between revisions
added F#
(→{{header|Go}}: updated to use new WaitGroup feature. also improved exception message.) |
(added F#) |
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}</lang>
=={{header|F_Sharp|F#}}==
The rendezvous mechanism is realized by using F#'s mailbox processors to implement active objects.
It is possible to extract the boilerplate code into a reusable helper class which should be considered when using active objects a lot.
<lang fsharp>open System
type PrinterCommand = Print of string
// a message is a command and a facility to return an exception
type Message = Message of PrinterCommand * AsyncReplyChannel<Exception option>
// thrown if we have no more ink (and neither has our possible backup printer)
exception OutOfInk
type Printer(id, ?backup:Printer) =
let mutable ink = 5
// the actual printing logic as a private function
let print line =
if ink > 0 then
printf "%d: " id
Seq.iter (printf "%c") line
printf "\n"
ink <- ink - 1
else
match backup with
| Some p -> p.Print line
| None -> raise OutOfInk
// use a MailboxProcessor to process commands asynchronously;
// if an exception occurs, we return it to the calling thread
let agent = MailboxProcessor.Start( fun inbox ->
async {
while true do
let! Message (command, replyChannel) = inbox.Receive()
try
match command with
| Print line -> print line
replyChannel.Reply None
with
| ex -> replyChannel.Reply (Some ex)
})
// public printing method:
// send Print command and propagate exception if one occurs
member x.Print line =
match agent.PostAndReply( fun replyChannel -> Message (Print line, replyChannel) ) with
| None -> ()
| Some ex -> raise ex
open System.Threading
do
let main = new Printer(id=1, backup=new Printer(id=2))
(new Thread(fun () ->
try
main.Print "Humpty Dumpty sat on a wall."
main.Print "Humpty Dumpty had a great fall."
main.Print "All the king's horses and all the king's men"
main.Print "Couldn't put Humpty together again."
with
| OutOfInk -> printfn " Humpty Dumpty out of ink!"
)).Start()
(new Thread(fun () ->
try
main.Print "Old Mother Goose"
main.Print "Would ride through the air"
main.Print "On a very fine gander."
main.Print "Jack's mother came in,"
main.Print "And caught the goose soon,"
main.Print "And mounting its back,"
main.Print "Flew up to the moon."
with
| OutOfInk -> printfn " Mother Goose out of ink!"
)).Start()
Console.ReadLine() |> ignore</lang>
Example output:
<pre>1: Old Mother Goose
1: Humpty Dumpty sat on a wall.
1: Would ride through the air
1: Humpty Dumpty had a great fall.
1: On a very fine gander.
2: All the king's horses and all the king's men
2: Jack's mother came in,
2: Couldn't put Humpty together again.
2: And caught the goose soon,
2: And mounting its back,
Mother Goose out of ink!</pre>
=={{header|Go}}==
Pretty sure printing could be done better ways in Go, but I stayed as close to the task description as I could.
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