Concurrent Memoization

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module Memoize

//More generic variant of http://www.fssnip.net/c4  
let memoize (f: 'a -> 'b) =
    let cache = System.Collections.Concurrent.ConcurrentDictionary<'a, 'b>()
    fun x -> cache.GetOrAdd(x, f)

// and this works also with F# async functions.
let memoizeAsync f =
    let cache = System.Collections.Concurrent.ConcurrentDictionary<'a, System.Threading.Tasks.Task<'b>>()
    fun x -> // task.Result serialization to sync after done.
        cache.GetOrAdd(x, fun x -> f(x) |> Async.StartAsTask) |> Async.AwaitTask

(*
[<Test>]
let ``async cache should work``() =
    let mutable x = 0
    let someSlowFunc mykey = async { 
        Console.WriteLine "Simulated downloading..."
        do! Async.Sleep 400
        Console.WriteLine "Simulated downloading Done."
        x <- x + 1 // Side effect!
        return "" }
    let memFunc = memoizeAsync <| someSlowFunc
    async {
        do! memFunc "a" |> Async.Ignore
        do! memFunc "a" |> Async.Ignore
        do! memFunc "a" |> Async.Ignore
        do! [|1 .. 30|] |> Seq.map(fun _ -> (memFunc "a")) 
            |> Async.Parallel |> Async.Ignore
        for i = 1 to 30 do
            Async.Start( memFunc "a" |> Async.Ignore )
            Async.Start( memFunc "a" |> Async.Ignore )
        do! Async.Sleep 500
        do! memFunc "a" |> Async.Ignore
        do! memFunc "a" |> Async.Ignore
        for i = 1 to 30 do
            Async.Start( memFunc "a" |> Async.Ignore )
        do! [|1 .. 30|] |> Seq.map(fun _ -> (memFunc "a")) 
            |> Async.Parallel |> Async.Ignore
    } |> Async.RunSynchronously
    x |> shouldEqual 1
*)

module Memoize

val memoize : f:('a -> 'b) -> ('a -> 'b)

Full name: Memoize.memoize

val f : ('a -> 'b)

val cache : System.Collections.Concurrent.ConcurrentDictionary<'a,'b>

namespace System

namespace System.Collections

namespace System.Collections.Concurrent

Multiple items
type ConcurrentDictionary<'TKey,'TValue> =
  new : unit -> ConcurrentDictionary<'TKey, 'TValue> + 6 overloads
  member AddOrUpdate : key:'TKey * addValueFactory:Func<'TKey, 'TValue> * updateValueFactory:Func<'TKey, 'TValue, 'TValue> -> 'TValue + 1 overload
  member Clear : unit -> unit
  member ContainsKey : key:'TKey -> bool
  member Count : int
  member GetEnumerator : unit -> IEnumerator<KeyValuePair<'TKey, 'TValue>>
  member GetOrAdd : key:'TKey * valueFactory:Func<'TKey, 'TValue> -> 'TValue + 1 overload
  member IsEmpty : bool
  member Item : 'TKey -> 'TValue with get, set
  member Keys : ICollection<'TKey>
  ...

Full name: System.Collections.Concurrent.ConcurrentDictionary<_,_>

--------------------
System.Collections.Concurrent.ConcurrentDictionary() : unit
System.Collections.Concurrent.ConcurrentDictionary(collection: System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<'TKey,'TValue>>) : unit
System.Collections.Concurrent.ConcurrentDictionary(comparer: System.Collections.Generic.IEqualityComparer<'TKey>) : unit
System.Collections.Concurrent.ConcurrentDictionary(concurrencyLevel: int, capacity: int) : unit
System.Collections.Concurrent.ConcurrentDictionary(collection: System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<'TKey,'TValue>>, comparer: System.Collections.Generic.IEqualityComparer<'TKey>) : unit
System.Collections.Concurrent.ConcurrentDictionary(concurrencyLevel: int, collection: System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<'TKey,'TValue>>, comparer: System.Collections.Generic.IEqualityComparer<'TKey>) : unit
System.Collections.Concurrent.ConcurrentDictionary(concurrencyLevel: int, capacity: int, comparer: System.Collections.Generic.IEqualityComparer<'TKey>) : unit

val x : 'a

System.Collections.Concurrent.ConcurrentDictionary.GetOrAdd(key: 'a, value: 'b) : 'b
System.Collections.Concurrent.ConcurrentDictionary.GetOrAdd(key: 'a, valueFactory: System.Func<'a,'b>) : 'b

val memoizeAsync : f:('a -> Async<'b>) -> ('a -> Async<'b>)

Full name: Memoize.memoizeAsync

val f : ('a -> Async<'b>)

val cache : System.Collections.Concurrent.ConcurrentDictionary<'a,System.Threading.Tasks.Task<'b>>

namespace System.Threading

namespace System.Threading.Tasks

Multiple items
type Task<'TResult> =
  inherit Task
  new : function:Func<'TResult> -> Task<'TResult> + 7 overloads
  member ContinueWith : continuationAction:Action<Task<'TResult>> -> Task + 9 overloads
  member Result : 'TResult with get, set
  static member Factory : TaskFactory<'TResult>

Full name: System.Threading.Tasks.Task<_>

--------------------
type Task =
  new : action:Action -> Task + 7 overloads
  member AsyncState : obj
  member ContinueWith : continuationAction:Action<Task> -> Task + 9 overloads
  member CreationOptions : TaskCreationOptions
  member Dispose : unit -> unit
  member Exception : AggregateException
  member Id : int
  member IsCanceled : bool
  member IsCompleted : bool
  member IsFaulted : bool
  ...

Full name: System.Threading.Tasks.Task

--------------------
System.Threading.Tasks.Task(function: System.Func<'TResult>) : unit
System.Threading.Tasks.Task(function: System.Func<'TResult>, cancellationToken: System.Threading.CancellationToken) : unit
System.Threading.Tasks.Task(function: System.Func<'TResult>, creationOptions: System.Threading.Tasks.TaskCreationOptions) : unit
System.Threading.Tasks.Task(function: System.Func<obj,'TResult>, state: obj) : unit
System.Threading.Tasks.Task(function: System.Func<'TResult>, cancellationToken: System.Threading.CancellationToken, creationOptions: System.Threading.Tasks.TaskCreationOptions) : unit
System.Threading.Tasks.Task(function: System.Func<obj,'TResult>, state: obj, cancellationToken: System.Threading.CancellationToken) : unit
System.Threading.Tasks.Task(function: System.Func<obj,'TResult>, state: obj, creationOptions: System.Threading.Tasks.TaskCreationOptions) : unit
System.Threading.Tasks.Task(function: System.Func<obj,'TResult>, state: obj, cancellationToken: System.Threading.CancellationToken, creationOptions: System.Threading.Tasks.TaskCreationOptions) : unit

--------------------
System.Threading.Tasks.Task(action: System.Action) : unit
System.Threading.Tasks.Task(action: System.Action, cancellationToken: System.Threading.CancellationToken) : unit
System.Threading.Tasks.Task(action: System.Action, creationOptions: System.Threading.Tasks.TaskCreationOptions) : unit
System.Threading.Tasks.Task(action: System.Action<obj>, state: obj) : unit
System.Threading.Tasks.Task(action: System.Action, cancellationToken: System.Threading.CancellationToken, creationOptions: System.Threading.Tasks.TaskCreationOptions) : unit
System.Threading.Tasks.Task(action: System.Action<obj>, state: obj, cancellationToken: System.Threading.CancellationToken) : unit
System.Threading.Tasks.Task(action: System.Action<obj>, state: obj, creationOptions: System.Threading.Tasks.TaskCreationOptions) : unit
System.Threading.Tasks.Task(action: System.Action<obj>, state: obj, cancellationToken: System.Threading.CancellationToken, creationOptions: System.Threading.Tasks.TaskCreationOptions) : unit

System.Collections.Concurrent.ConcurrentDictionary.GetOrAdd(key: 'a, value: System.Threading.Tasks.Task<'b>) : System.Threading.Tasks.Task<'b>
System.Collections.Concurrent.ConcurrentDictionary.GetOrAdd(key: 'a, valueFactory: System.Func<'a,System.Threading.Tasks.Task<'b>>) : System.Threading.Tasks.Task<'b>

Multiple items
type Async
static member AsBeginEnd : computation:('Arg -> Async<'T>) -> ('Arg * AsyncCallback * obj -> IAsyncResult) * (IAsyncResult -> 'T) * (IAsyncResult -> unit)
static member AwaitEvent : event:IEvent<'Del,'T> * ?cancelAction:(unit -> unit) -> Async<'T> (requires delegate and 'Del :> Delegate)
static member AwaitIAsyncResult : iar:IAsyncResult * ?millisecondsTimeout:int -> Async<bool>
static member AwaitTask : task:Task -> Async<unit>
static member AwaitTask : task:Task<'T> -> Async<'T>
static member AwaitWaitHandle : waitHandle:WaitHandle * ?millisecondsTimeout:int -> Async<bool>
static member CancelDefaultToken : unit -> unit
static member Catch : computation:Async<'T> -> Async<Choice<'T,exn>>
static member FromBeginEnd : beginAction:(AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg:'Arg1 * beginAction:('Arg1 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg1:'Arg1 * arg2:'Arg2 * beginAction:('Arg1 * 'Arg2 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg1:'Arg1 * arg2:'Arg2 * arg3:'Arg3 * beginAction:('Arg1 * 'Arg2 * 'Arg3 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromContinuations : callback:(('T -> unit) * (exn -> unit) * (OperationCanceledException -> unit) -> unit) -> Async<'T>
static member Ignore : computation:Async<'T> -> Async<unit>
static member OnCancel : interruption:(unit -> unit) -> Async<IDisposable>
static member Parallel : computations:seq<Async<'T>> -> Async<'T []>
static member RunSynchronously : computation:Async<'T> * ?timeout:int * ?cancellationToken:CancellationToken -> 'T
static member Sleep : millisecondsDueTime:int -> Async<unit>
static member Start : computation:Async<unit> * ?cancellationToken:CancellationToken -> unit
static member StartAsTask : computation:Async<'T> * ?taskCreationOptions:TaskCreationOptions * ?cancellationToken:CancellationToken -> Task<'T>
static member StartChild : computation:Async<'T> * ?millisecondsTimeout:int -> Async<Async<'T>>
static member StartChildAsTask : computation:Async<'T> * ?taskCreationOptions:TaskCreationOptions -> Async<Task<'T>>
static member StartImmediate : computation:Async<unit> * ?cancellationToken:CancellationToken -> unit
static member StartWithContinuations : computation:Async<'T> * continuation:('T -> unit) * exceptionContinuation:(exn -> unit) * cancellationContinuation:(OperationCanceledException -> unit) * ?cancellationToken:CancellationToken -> unit
static member SwitchToContext : syncContext:SynchronizationContext -> Async<unit>
static member SwitchToNewThread : unit -> Async<unit>
static member SwitchToThreadPool : unit -> Async<unit>
static member TryCancelled : computation:Async<'T> * compensation:(OperationCanceledException -> unit) -> Async<'T>
static member CancellationToken : Async<CancellationToken>
static member DefaultCancellationToken : CancellationToken

Full name: Microsoft.FSharp.Control.Async

--------------------
type Async<'T>

Full name: Microsoft.FSharp.Control.Async<_>

static member Async.StartAsTask : computation:Async<'T> * ?taskCreationOptions:System.Threading.Tasks.TaskCreationOptions * ?cancellationToken:System.Threading.CancellationToken -> System.Threading.Tasks.Task<'T>

static member Async.AwaitTask : task:System.Threading.Tasks.Task -> Async<unit>
static member Async.AwaitTask : task:System.Threading.Tasks.Task<'T> -> Async<'T>