I wrote a simple TCP-client for some device, which consumes and produces 8-byte packets (the code of send-command-receive-result function is below).
When I run it on linux, it works perfectly, being part of the loop (send-recv-send-recv-...), but on windows it receives only first msg from device (send-recv-send-send-...). The packets are still going - I could clearly see them with Wireshark - but something under my client just ignores them (or truncates to zero?). It doesn't even print "Data was read!" - looks like the reading stucks and gets killed by timeout function.
Before that, I used the sockets directly; changing to HandleStream yelded no difference at all. Wrapping main in withSocketsDo did nothing, too.
transmit :: Int -> HandleStream ByteString -> ByteString -> IO [Bytestring]
transmit delay sock packet = do
let input = timeout delay $ sock `readBlock` 8 <* putStrLn "\nData was read!"
sock `writeBlock` pack
strings <- whileJust input
return [str | Right str <- strings]
whileJust action = do
result <- action
case result of
Just a -> (:) <$> return a <*> whileJust action
Nothing -> return []
What am I doing wrong?
Related
I am experimenting with Suave to send a stream of data updates; I want to replace a system we have that does polling with a socket implementation.
Here's some code:
let updateStreamSocket (webSocket : WebSocket) (context: HttpContext) =
socket {
printfn "connection"
candleUpdateEvent.Publish.Add(fun d ->
(webSocket.send Binary (d |> ByteSegment) true |> Async.RunSynchronously |> ignore)
)
let mutable loop = true
while loop do
let! msg = webSocket.read()
match msg with
| (Close, _, _) ->
let emptyResponse = [||] |> ByteSegment
do! webSocket.send Close emptyResponse true
loop <- false
| _ -> ()
printfn "disconnection"
}
Since I'm testing, I just care about the Close message, but eventually I'll have to process the Text messages to handle subscriptions.
The model is that data gets processed and each batch triggers an event (through a mailbox processor to separate threads). In the socket code, I need to handle both the socket messages I receive but also these events to send the data.
How could I join this in a single loop and wait for either event?
Right now the event handler in the socket {} section will be added / removed with connection / disconnections, but it would be possible that the close get called and then an event arrives and tries to send data, etc.. while it works while testing, this is not right.
I am trying to solve the following problem. I have some agents running in real-time, with a large heartbeat of couple of milliseconds, and the order of operations they process for this reason are mostly deterministic (as the message processing is not the bottleneck).
Now, I am running a large amount of simulations of the system where I no longer have a heartbeat (otherwise it will take a couple of centuries) - but I need to make sure the order of operations are preserved. For this, I adopted the following solution: the simulator makes sure each agent has processed his message queue, by posting a dummy synchronization message and blocking while waiting for the answer. This does work for my application, but the time it takes is not intuitive - as a single threaded implementation would be an order of magnitude faster (I guess - x 100 ish - although I have not tested ).
I have isolated a small test that shows the issue, even trying to use another library, akka.net
type Greet =
| Greet of string
| Hello of AsyncReplyChannel<bool>
| Hello2
[<EntryPoint>]
let main argv =
let system = System.create "MySystem" <| Configuration.load()
let greeter = spawn system "greeter" <| fun mailbox ->
let rec loop() = actor {
let! msg = mailbox.Receive()
let sender = mailbox.Sender()
match msg with
| Greet who -> () // printf "Hello, %s!\n" who
| Hello2 -> sender.Tell(true)
| _ -> ()
return! loop()
}
loop()
let greeterF =
MailboxProcessor.Start
(fun inbox ->
async {
while true do
let! msg = inbox.Receive()
match msg with
| Greet who -> () // printf "Hello, %s!\n" who
| Hello reply -> reply.Reply true
| _ -> ()
}
)
let n = 1000000
let t1 = System.Diagnostics.Stopwatch()
t1.Start()
for i = 1 to n do
let rep = greeterF.PostAndReply(fun reply -> (Hello reply)) |> ignore
()
printfn "elapsed Mailbox:%A" t1.ElapsedMilliseconds
t1.Restart()
for i = 1 to n do
let res = greeter.Ask (Hello2)
let rr = res.Result
()
printfn "elapsed Akka:%A" t1.ElapsedMilliseconds
System.Console.ReadLine () |> ignore
0
Basically, both take about 10 seconds for a mere 1 millions of synchronizations - and not computation what-so-ever involved, and this is... unfortunate.
I am wondering if anybody has come across the same problem and if there is anyway to switch off the overhead forcing everything to run in a single threaded mode... something like better than de-activating all the cpus but 1 in the bios - or writing a clone of the whole system without the agents.
Any help well appreciated.
The reason for the Akka.NET version beeing slow here is how you communicate with the actor:
main process Task FutureActorRef !!ThreadPool!! greeter
Ask ---------------------->
Tell----------->
MailboxRun ----->
(greeter mailbox is empty) |
<--------------------------Tell
<--Complete task
<----------.Result
For each iteration, a TPL task will be created
Then a single message is sent to the greeter.
The main process then blocks while waiting for the response to come back.
The greeter replies back which in turn completes the task inside the FutureActorRef
Rinse and Repeat..
This design will cause Akka.NET to start and stop the greeters "mailbox run" for each message as the mailbox queue becomes empty for each iteration.
This results in threadpool schedulation for each single message that is passed.
It's a bit like entering your car, putting the pedal to the metal, then abruptly stop and step out of the car, and then repeating the procedure again.
That is just not a very effective way to travel fast.
#Aaronontheweb's suggestion will only have effect if you work out the above kinks in your code.
The mailbox needs to be able to constantly pick messages of the internal queue to work with messages in batches to achieve full throughput.
Instead, separate the producer from the consumer.
Create an actor that listens for the responses from your greeter.
And once that actor have processes your 1000000 messages, let that actor send a WorkCompleted message back to the consumer.
[Edit]
I gave it a shot myself, I don't know F# so it might not be completely idiomatic :)
open Akka
open Akka.Actor
open Akka.FSharp
type Greet =
| Greet of string
| Hello of AsyncReplyChannel<bool>
| Hello2
type Consume =
| Response
| SetSender
[<EntryPoint>]
let main argv =
let system = System.create "MySystem" <| Configuration.load()
let greeter = spawn system "greeter" <| fun mailbox ->
let rec loop() = actor {
let! msg = mailbox.Receive()
let sender = mailbox.Sender()
match msg with
| Greet who -> () // printf "Hello, %s!\n" who
| Hello2 -> sender.Tell(Response)
| _ -> ()
return! loop()
}
loop()
let consumer = spawn system "consumer" <| fun mailbox ->
let rec loop(count,sender : IActorRef) = actor {
if count = 1000000 then sender.Tell(true)
let! msg = mailbox.Receive()
match msg with
| Response -> return! loop(count+1,sender)
| SetSender -> return! loop(count,mailbox.Sender())
}
loop(0,null)
let n = 1000000
let t1 = System.Diagnostics.Stopwatch()
t1.Start()
for i = 1 to n do
greeter.Tell(Hello2,consumer)
let workdone = consumer.Ask SetSender
workdone.Wait()
printfn "elapsed Akka:%A" t1.ElapsedMilliseconds
System.Console.ReadLine () |> ignore
0
I updated your code to use a separate consumer for the actor responses and then reply back once all replies had been processed.
By doing so, your processing time is now down to 650ms on my machine.
If you want better throughput, you need to involve more actors to parallelize more.
I'm not sure if this helps in your specific scenario
Here is a slightly modified MailboxProcessor version:
module MBPAsync =
type Greet =
| Greet of string
| Hello of AsyncReplyChannel<bool>
let run n =
let timer = Stopwatch.StartNew ()
use greeter =
MailboxProcessor.Start <| fun inbox -> async {
while true do
let! msg = inbox.Receive()
match msg with
| Greet who -> () // printf "Hello, %s!\n" who
| Hello reply -> reply.Reply true
}
Async.RunSynchronously <| async {
for i = 1 to n do
do! Async.Ignore (greeter.PostAndAsyncReply Hello)
}
let elapsed = timer.Elapsed
printfn "%A" elapsed
The difference here is that this version uses PostAndAsyncReply and keeps the computation in an async workflow. On my quick test this seemed to be much faster that using PostAndReply, but YMMV.
The timings I get from the above MBP version look roughly like this:
> MBPAsync.run 1000000 ;;
00:00:02.6883486
val it : unit = ()
A comment earlier mentioned my Hopac library. Here is an optimized version using Hopac:
module Hop =
type Greet =
| Greet of string
| Hello of IVar<bool>
let run n =
let timer = Stopwatch.StartNew ()
let greeterCh = ch ()
do greeterCh >>= function
| Greet who -> Job.unit ()
| Hello reply -> reply <-= true
|> Job.forever
|> server
Job.forUpToIgnore 1 n <| fun _ ->
let reply = ivar ()
greeterCh <-- Hello reply >>.
reply
|> run
let elapsed = timer.Elapsed
printfn "%A" elapsed
The timings I get from the above Hopac version look roughly like this:
> Hop.run 1000000 ;;
00:00:00.1088768
val it : unit = ()
I'm not an F# developer, but I'm a core dev on Akka.NET. A couple of ideas for your scenario:
If you're only using a single actor for this work, you can try using a PinnedDispatcher - that way the actor runs on its own dedicated thread all the time. That will save you on unnecessary context switching overhead.
You can also set the throughput of the mailbox to be much higher for this PinnedDispatcher than the normal settings. i.e. set a throughput value of 10000 (or something) instead of the normal 25. Assuming that the contents of your mailbox grow in large bursts this should save you on mailbox synchronization overhead.
Here's what your dispatcher configuration might look like:
my-pinned-dispatcher {
type = PinnedDispatcher
throughput = 1000 #your mileage may vary
}
And then configure an actor to use it
C# Fluent Interface
var myActor = myActorSystem.ActorOf(Props.Create<FooActor>()
.WithDispatcher("my-pinned-dispatcher");
Config
akka.actor.deployment{
/greeter{
dispatcher = my-pinned-dispatcher
}
}
These are both options you can configure via HOCON in App.config or Web.config or you can use the fluent interface on the Props class to do this. Also worth noting: there's a bug with pinned dispatchers at the moment, but that should be fixed in our next maintenance release (v1.0.1,) which should be out next week.
Your mileage may vary, but this is what I would try - basically it's just designed to help reduce contention and overhead around a single actor.
I am converting the OCaml Format module to F# and tracked a problem back to a use of the OCaml Pervasives at_exit.
val at_exit : (unit -> unit) -> unit
Register the given function to be called at program termination time. The functions registered with at_exit will be called when the program executes exit, or terminates, either normally or because of an uncaught exception. The functions are called in "last in, first out" order: the function most recently added with at_exit is called first.
In the process of conversion I commented out the line as the compiler did not flag it as being needed and I was not expecting an event in the code.
I checked the FSharp.PowerPack.Compatibility.PervasivesModule for at_exit using VS Object Browser and found none.
I did find how to run code "at_exit"? and How do I write an exit handler for an F# application?
The OCaml line is
at_exit print_flush
with print_flush signature: val print_flush : (unit -> unit)
Also in looking at the use of it during a debug session of the OCaml code, it looks like at_exit is called both at the end of initialization and at the end of each use of a call to the module.
Any suggestions, hints on how to do this. This will be my first event in F#.
EDIT
Here is some of what I have learned about the Format module that should shed some light on the problem.
The Format module is a library of functions for basic pretty printer commands of simple OCaml values such as int, bool, string. The format module has commands like print_string, but also some commands to say put the next line in a bounded box, think new set of left and right margins. So one could write:
print_string "Hello"
or
open_box 0; print_string "<<";
open_box 0; print_string "p \/ q ==> r"; close_box();
print_string ">>"; close_box()
The commands such as open_box and print_string are handled by a loop that interprets the commands and then decides wither to print on the current line or advance to the next line. The commands are held in a queue and there is a state record to hold mutable values such as left and right margin.
The queue and state needs to be primed, which from debugging the test cases against working OCaml code appears to be done at the end of initialization of the module but before the first call is made to any function in the Format module. The queue and state is cleaned up and primed again for the next set of commands by the use of mechanisms for at_exit that recognize that the last matching frame for the initial call to the format modules has been removed thus triggering the call to at_exit which pushes out any remaining command in the queue and re-initializes the queue and state.
So the sequencing of the calls to print_flush is critical and appears to be at more than what the OCaml documentation states.
This should do it:
module Pervasives =
open System
open System.Threading
//
let mutable private exitFunctions : (unit -> unit) list = List.empty
//
let mutable private exitFunctionsExecutedFlag = 0
//
let private tryExecuteExitFunctions _ =
if Interlocked.CompareExchange (&exitFunctionsExecutedFlag, 1, 0) = 0 then
// Run the exit functions in last-in-first-out order.
exitFunctions
|> List.iter (fun f -> f ())
// Register handlers for events which fire when the process exits cleanly
// or due to an exception being thrown.
do
AppDomain.CurrentDomain.ProcessExit.Add tryExecuteExitFunctions
AppDomain.CurrentDomain.UnhandledException.Add tryExecuteExitFunctions
//
let at_exit f =
// TODO : This function should be re-written using atomic operations
// for thread-safety!
exitFunctions <- f :: exitFunctions
And some code to test it:
open System
// Register a couple of handlers to test our code.
Pervasives.at_exit <| fun () ->
Console.WriteLine "The first registered function has fired!"
Pervasives.at_exit <| fun () ->
Console.WriteLine "The second registered function has fired!"
TimeSpan.FromSeconds 1.0
|> System.Threading.Thread.Sleep
Console.WriteLine "Exiting the second registered function!"
Pervasives.at_exit <| fun () ->
Console.WriteLine "The third registered function has fired!"
// Do some stuff in our program
printfn "blah"
printfn "foo"
printfn "bar"
(* The functions we registered with at_exit should be fired here. *)
// Uncomment this to see that our handlers work even when the
// program crashes due to an unhandled exception.
//failwith "Uh oh!"
I intend to build on this code, found here
However, I notice I can telnet to this server on the local host. Can't from another computer. I did a quick nmap scan, which reported that nothing was listening on the port I had selected.
For purposes of troubleshooting, I had shut down my firewall, so I've ruled that out as a possible problem.
Clues from haskell windows programmers would be appreciated.
It seems that the socket got bind to localhost (127.0.0.1), thats why you are not able to connect it from other machine and it only connect from local machine. Try to use Bind API to first create the socket and then bind the socket to "Any address" which binds the socket to every interface available on local machine.
This is for future new haskellers.
I based my code on this example.
I made improvements based on this reddit thread, and suggestions made above. The import statements are still sloppy, but fixing them is left as the proverbial "exercise for the reader". I invite any additional suggestions leading to improvements.
import Network.Socket
import Control.Monad
import Network
import System.Environment (getArgs)
import System.IO
import Control.Concurrent (forkIO)
main :: IO ()
main = withSocketsDo $ do
[portStr] <- getArgs
sock <- socket AF_INET Stream defaultProtocol
let port = fromIntegral (read portStr :: Int)
socketAddress = SockAddrInet port 0000
bindSocket sock socketAddress
listen sock 1
putStrLn $ "Listening on " ++ (show port)
sockHandler sock
sockHandler :: Socket -> IO ()
sockHandler sock' = forever $ do
(sock, _) <- Network.Socket.accept sock'
handle <- socketToHandle sock ReadWriteMode
hSetBuffering handle NoBuffering
forkIO $ commandProcessor handle
commandProcessor :: Handle -> IO ()
commandProcessor handle = forever $ do
line <- hGetLine handle
let (cmd:arg) = words line
case cmd of
"echo" -> echoCommand handle arg
"add" -> addCommand handle arg
_ -> do hPutStrLn handle "Unknown command"
echoCommand :: Handle -> [String] -> IO ()
echoCommand handle arg = do
hPutStrLn handle (unwords arg)
addCommand :: Handle -> [String] -> IO ()
addCommand handle [x,y] = do
hPutStrLn handle $ show $ read x + read y
addCommand handle _ = do
hPutStrLn handle "usage: add Int Int"
I usually go with
netstat -an | grep LISTEN
If you see the port listed, something is listening. I can't remember offhand what the lsof command is for sockets and Google isn't giving up the goods.
I've tried this:
main = do
hSetBuffering stdin NoBuffering
c <- getChar
but it waits until the enter is pressed, which is not what I want. I want to read the character immediately after user presses it.
I am using ghc v6.12.1 on Windows 7.
EDIT: workaround for me was moving from GHC to WinHugs, which supports this correctly.
Yes, it's a bug. Here's a workaround to save folks clicking and scrolling:
{-# LANGUAGE ForeignFunctionInterface #-}
import Data.Char
import Foreign.C.Types
getHiddenChar = fmap (chr.fromEnum) c_getch
foreign import ccall unsafe "conio.h getch"
c_getch :: IO CInt
So you can replace calls to getChar with calls to getHiddenChar.
Note this is a workaround just for ghc/ghci on Windows. For example, winhugs doesn't have the bug and this code doesn't work in winhugs.
Might be a bug:
http://hackage.haskell.org/trac/ghc/ticket/2189
The following program repeats inputted characters until the escape key is pressed.
import IO
import Monad
import Char
main :: IO ()
main = do hSetBuffering stdin NoBuffering
inputLoop
inputLoop :: IO ()
inputLoop = do i <- getContents
mapM_ putChar $ takeWhile ((/= 27) . ord) i
Because of the hSetBuffering stdin NoBuffering line it should not be necessary to press the enter key between keystrokes. This program works correctly in WinHugs (sep 2006 version). However, GHC 6.8.2 does not repeat the characters until the enter key is pressed. The problem was reproduced with all GHC executables (ghci, ghc, runghc, runhaskell), using both cmd.exe and command.com on Windows XP Professional...
Hmm.. Actually I can't see this feature to be a bug. When you read stdin that means that you want to work with a "file" and when you turn of buffering you are saying that there is no need for read buffer. But that doesn't mean that application which is emulating that "file" should not use write buffer. For linux if your terminal is in "icanon" mode it doesn't send any input until some special event will occur (like Enter pressed or Ctrl+D). Probably console in Windows have some similar modes.
The Haskeline package worked for me.
If you need it for individual characters, then just change the sample slightly.
getInputLine becomes getInputChar
"quit" becomes 'q'
++ input becomes ++ [input]
main = runInputT defaultSettings loop
where
loop :: InputT IO ()
loop = do
minput <- getInputChar "% "
case minput of
Nothing -> return ()
Just 'q' -> return ()
Just input -> do outputStrLn $ "Input was: " ++ [input]
loop
From comment of #Richard Cook:
Use hidden-char: Provides cross-platform getHiddenChar function.
I used the haskeline package, suggested in other answers, to put together this simple alternative to getChar. It requests input again in the case that getInputChar returns Nothing. This worked for me to get past the issue; modify as needed.
import System.Console.Haskeline
( runInputT
, defaultSettings
, getInputChar
)
betterInputChar :: IO Char
betterInputChar = do
mc <- runInputT defaultSettings (getInputChar "")
case mc of
Nothing -> betterInputChar
(Just c) -> return c