Created
March 13, 2012 03:07
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Asynchronous log writer implemented using F# agent
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| module LogAgent = | |
| // Log writer implementation using F# asynchronous agents | |
| // Written as an excersise | |
| open System | |
| open System.IO | |
| type private Message = | |
| | Debug of string | |
| | Info of string | |
| | Warn of string | |
| | Error of string | |
| | Fatal of string | |
| with | |
| static member toString logMessage = | |
| match logMessage with | |
| | Debug m -> m |> sprintf "DEBUG:%s" | |
| | Info m -> m |> sprintf "INFO:%s" | |
| | Warn m -> m |> sprintf "WARN:%s" | |
| | Error m -> m |> sprintf "ERROR:%s" | |
| | Fatal m -> m |> sprintf "FATAL:%s" | |
| override this.ToString() = | |
| Message.toString this | |
| type private LogCommand = | |
| | Log of Message | |
| | Flush | |
| | Close of AsyncReplyChannel<unit> | |
| type LogAgent(logFile:string) as this = | |
| let writer = lazy(File.AppendText logFile) | |
| let agent = MailboxProcessor.Start (fun agent -> | |
| // Do the loop until the Stop command is received | |
| // Keep the number of lines written to the log | |
| let rec loop(count) = async { | |
| let! command = agent.Receive() | |
| match command with | |
| | Log message -> | |
| let count = count + 1 | |
| let message = Message.toString message | |
| writer.Value.WriteLine message | |
| return! loop(count) | |
| | Flush -> | |
| if writer.IsValueCreated then | |
| writer.Value.Flush() | |
| return! loop(count) | |
| | Close reply -> | |
| let message = sprintf "%d messages written into log" count | |
| Console.WriteLine message | |
| this.doClose() | |
| reply.Reply(ignore()) | |
| return ignore() | |
| } | |
| loop(0)) | |
| interface IDisposable with | |
| member this.Dispose() = this.doClose() | |
| member private this.doClose() = | |
| let message = sprintf "Discarding %d messages in the queue" (agent.CurrentQueueLength) | |
| Console.WriteLine(message) | |
| let d = agent :> IDisposable | |
| d.Dispose() | |
| if writer.IsValueCreated then | |
| writer.Value.Dispose() | |
| member private this.log objToMessage obj = | |
| obj |> objToMessage |> LogCommand.Log |> agent.Post | |
| member this.fatal = this.log Fatal; | |
| member this.error = this.log Error | |
| member this.warn = this.log Warn | |
| member this.info = this.log Info | |
| member this.debug = this.log Debug | |
| member this.queueLength = agent.CurrentQueueLength | |
| member this.flush() = LogCommand.Flush |> agent.Post | |
| member this.close() = LogCommand.Close |> agent.PostAndReply | |
| module Demo = | |
| open LogAgent | |
| let usage() = | |
| // Create log. | |
| // Can bind with "use" if we want to dispose of it automatically. | |
| // Otherwise can bind with let and call "close" manually. | |
| use log = new LogAgent(@"c:\temp\foo.log") | |
| // pump lots of log messages asynchronously | |
| let pump = async { | |
| [0..20000] | |
| |> Seq.iter (fun i -> sprintf "Log #%d" i |> log.info) | |
| } | |
| Async.Start pump | |
| // wait for a bit for the pump to push through some messages and then close | |
| System.Threading.Thread.Sleep(100) | |
| log.close() | |
| // Sleep a bit and see that the pump is still going, but messages | |
| // are not written anywhere. No error reported. Is this the behaviour | |
| // we want? | |
| printfn "Sleeping for 2 seconds" | |
| System.Threading.Thread.Sleep(2000) | |
| [<EntryPoint>] | |
| let main(_) = | |
| usage() | |
| 0 |
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