2

此代码在 Mono (5.4.1.7) 上运行。

我正在使用 F# 的代理来处理我的 Web 应用程序中的大量数据处理,其中一条消息是 Shutdown。处理已发布的 Shutdown 消息时,代理会清理一些内容并停止其消息循环。这很好用,但如果我尝试从Finalize(). 我设法重现了这个:

open System
open System.Threading

type ConsoleMessage =
    | Clear
    | Println of string
    // Reply back (with unit) so that calling code is able to wait for the agent to clean up (for code dependent on the
    // agent's resources definitely being released and such)
    | Shutdown of AsyncReplyChannel<unit>

type ConsoleAgent() =
    let mutable disposed = false
    let mutable stopped = false

    let agent = MailboxProcessor.Start(fun agent ->
        let rec messageLoop () = async {
            let! message = agent.Receive ()
            match message with
            | Clear -> System.Console.Clear ()
            | Println str -> printfn "%s" str
            | Shutdown rc ->
                // Cleanup goes here
                printfn "Shutting Down"
                stopped <- true
                rc.Reply ()
            System.Threading.Thread.Sleep 100
            if not stopped then
                return! messageLoop () }
        messageLoop ())

    member this.Post msg = agent.Post msg

    member this.PostAndAsyncReply msg = agent.PostAndAsyncReply msg

    member this.Dispose disposing =
        printfn "Disposing (disposing = %b)" disposing
        if not disposed then
            Async.RunSynchronously (agent.PostAndAsyncReply Shutdown)
            disposed <- true

    override this.Finalize () =
        this.Dispose false

    interface IDisposable with
        member this.Dispose () =
            this.Dispose true

module Main =
    [<EntryPoint>]
    let main args =
        let console = new ConsoleAgent()
        console.Post (Println "Print 1")
        console.Post (Println "Print 2")
        Thread.Sleep 1000
        0

当然,在实际应用程序中,它们与控制台打印无关。

这是我得到的堆栈跟踪:

Unhandled Exception:
System.NullReferenceException: Object reference not set to an instance of an object
  at System.Runtime.Remoting.Contexts.SynchronizationAttribute.EnterContext () [0x00000] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/corlib/System.Runtime.Remoting.Contexts/SynchronizationAttribute.cs:184 
  at System.Threading.WaitHandle.WaitOneNative (System.Runtime.InteropServices.SafeHandle waitableSafeHandle, System.UInt32 millisecondsTimeout, System.Boolean hasThreadAffinity, System.Boolean exitContext) [0x0002d] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/corlib/System.Threading/WaitHandle.cs:111 
  at System.Threading.WaitHandle.InternalWaitOne (System.Runtime.InteropServices.SafeHandle waitableSafeHandle, System.Int64 millisecondsTimeout, System.Boolean hasThreadAffinity, System.Boolean exitContext) [0x00014] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/threading/waithandle.cs:250 
  at System.Threading.WaitHandle.WaitOne (System.Int64 timeout, System.Boolean exitContext) [0x00000] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/threading/waithandle.cs:239 
  at System.Threading.WaitHandle.WaitOne (System.Int32 millisecondsTimeout, System.Boolean exitContext) [0x00019] in /Users/builder/data/lanes/4992/mono-mac-sdk/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/threading/waithandle.cs:206 
  at Microsoft.FSharp.Control.AsyncImpl+ResultCell`1[T].TryWaitForResultSynchronously (Microsoft.FSharp.Core.FSharpOption`1[T] timeout) [0x0002a] in <5a7d678a904cf4daa74503838a677d5a>:0 
  at Microsoft.FSharp.Control.CancellationTokenOps.RunSynchronouslyInCurrentThread[a] (System.Threading.CancellationToken token, Microsoft.FSharp.Control.FSharpAsync`1[T] computation) [0x0001c] in <5a7d678a904cf4daa74503838a677d5a>:0 
  at Microsoft.FSharp.Control.CancellationTokenOps.RunSynchronously[a] (System.Threading.CancellationToken token, Microsoft.FSharp.Control.FSharpAsync`1[T] computation, Microsoft.FSharp.Core.FSharpOption`1[T] timeout) [0x00013] in <5a7d678a904cf4daa74503838a677d5a>:0 
  at Microsoft.FSharp.Control.FSharpAsync.RunSynchronously[T] (Microsoft.FSharp.Control.FSharpAsync`1[T] computation, Microsoft.FSharp.Core.FSharpOption`1[T] timeout, Microsoft.FSharp.Core.FSharpOption`1[T] cancellationToken) [0x00070] in <5a7d678a904cf4daa74503838a677d5a>:0 
  at Program+ConsoleAgent.Dispose (System.Boolean disposing) [0x00027] in /Users/jwostenberg/Code/FSharp/Sandbox/Sandbox/Program.fs:38 
  at Program+ConsoleAgent.Finalize () [0x00000] in /Users/jwostenberg/Code/FSharp/Sandbox/Sandbox/Program.fs:42 

let console = new ConsoleAgent()更重要的是,如果对象通过 dispose 模式正确处理(例如更改为use console = new ConsoleAgent()),则不会发生这种情况。我不能在我自己的代码中真正做到这一点而不向后弯腰,因为我没有直接引用这些代理(其中有很多同时运行),但我不应该让他们通过反正垃圾收集器?

这是我的错,F# 的错,还是 Mono 的错?现在,我已经将 Dispose() 方法的相关部分包装在一个只记录异常的 try/catch 中,但这感觉真的很脏。

4

2 回答 2

2

您需要覆盖的场景很少Finalize,而且看起来您的用例并不适用。请参阅此处的“实施者注意事项”部分和整篇文章

默认情况下,该Object.Finalize方法不执行任何操作,但您应该仅在必要时重写 Finalize,并且仅用于释放非托管资源。

回复:您的评论:

您如何确保在MailboxProcessor没有 的情况下关闭消息循环Finalize

您可以只使用该IDisposable模式,或者MailboxProcessor更明确地管理您的 s 的生命周期,这可能需要重构您的项目。

我不能在我自己的代码中真正做到这一点而不向后弯腰,因为我没有直接引用这些代理(一次有很多代理运行),但我不应该让他们通过反正垃圾收集器?

是的,假设他们不拥有非托管资源,您应该能够让他们“自然地”处置。没有看到真实世界的用例就很难说,但听起来你想要更多地控制处理器的生命周期。这可能有点XY 问题

于 2018-02-25T18:09:44.443 回答
2

Dispose 方法的参数“处理”在这里是有原因的。它区分了 Dispose 的托管和非托管应用程序。简而言之,Dispose(true) 意味着此调用是显式的(使用语句或 F#'s use)。它基本上是“正常”.NET 编程的延续。

Dispose(false) 意味着完成正在发生。这意味着任何引用的 .NET 对象都可以是活动的、已处置的或已完成的。所以你的代码只需要关心非托管资源,不要尝试以任何其他方式调用或使用托管对象。

重要的是,Dispose() 不会自动调用,而 finaliser 会自动调用。使示例正确需要两个更改:

  • 显式控制一次性对象的状态
  • 仅在对象被释放时才发送消息,而不是最终确定

代码:

    member this.Dispose disposing =
        if disposing && not disposed then
            Async.RunSynchronously (agent.PostAndAsyncReply Shutdown)
            disposed <- true

module Main =
    [<EntryPoint>]
    let main args =
        use console = new ConsoleAgent()
        Thread.Sleep 1000
        0
于 2018-02-25T20:22:58.823 回答