我正在尝试编写一个f#计算表达式,它只允许从临界区内读写线程安全变量。
我有一个类型ThreadSafeVar<'t>
,它包装了一个值,一个CriticalSection<'t>
和一个计算表达式构建器LockContext
,如下所示:
// wraps a value and restricts access to it
type ThreadSafeVar<'t> (value: 't) =
member val internal Value = value with get, set
// Encapsulates a critical section
type CriticalSection<'t> =
private
{ LockObj: obj
fn: unit -> 't }
static member Lock(lc: CriticalSection<'t>) = lock lc.LockObj lc.fn
// Expression builder for a locked context
type LockContext () =
member internal this.SyncRoot = obj()
member this.Return(value: 'v) = value
member this.ReturnFrom(value: ThreadSafeVar<'t>) = value.Value
member __.Bind(value: ThreadSafeVar<'t>, fn: 't -> 'u) = fn value.Value
// returns a CriticalSection
member this.Run(fn : unit -> 'u) = { LockObj = this.SyncRoot
fn=fn }
.
.
.
由于Bind
,从锁上下文中读取线程安全值非常简单。例如
let lockedInt = ThreadSafeVar(1) // create a thread-safe variable
let context = LockContext()
let wrapperVal = context {
let! i = lockedInt // get the wrapper value inside lockedInt
return i
} |> CriticalSection.Lock
但是我正在努力理解如何实现从LockContext
实例中设置值的方法。因此,我采用的方法是实现一个自定义操作,例如,称为setVal
。到目前为止,我已经尝试过了,但我担心它们只是把水搅浑了。似乎自定义操作操作到目前为止在表达式内构建的计算,编码为元组,但我不认为在我的情况下需要这样做。
任何提示,指向资源,或直接帮助将不胜感激。
我不确定这样做是否明智,但我提出了一些基于State单子的方法,可能对您有用。首先,定义一个"有状态的"函数作为接受ThreadSafeVar
并返回某种类型结果的函数:
ThreadSafeVar<'state> -> 'result
然后将该签名放入表示有状态计算的类型中:
type Stateful<'state, 'result> =
MkStateful of (ThreadSafeVar<'state> -> 'result)
现在我们需要一种方法来安全地运行这样的计算,使用给定的TSV:
let run (tsv : ThreadSafeVar<_>) (MkStateful f) =
lock tsv (fun () -> f tsv)
请注意,我已经摆脱了你的CriticalSection
类型,而只是锁定TSV本身。
let lift value =
MkStateful (fun _ -> value)
以及将两个有状态计算绑定在一起的方法:
let bind binder stateful =
MkStateful (fun tsv ->
run tsv stateful
|> binder
|> run tsv)
定义构建器是很简单的:
type LockContext () =
member __.Return(value) = lift value
member __.Bind(stateful, binder) = bind binder stateful
let context = LockContext()
我们还需要辅助计算来安全地设置和获取值:
let getValue =
MkStateful (fun tsv ->
tsv.Value)
let setValue value =
MkStateful (fun tsv ->
tsv.Value <- value)
把所有这些放在一起,我们可以定义一个增加TSV值的计算:
let comp =
context {
let! oldValue = getValue
let newValue = oldValue + 1
do! setValue newValue
return newValue
}
我们可以这样运行:
let lockedInt = ThreadSafeVar(1)
let result = comp |> run lockedInt
printfn "%A" result // output is: 2
你可以在这里看到完整的解决方案并自己尝试。