7 people like it.

Circular Buffer

A Circular, or Ring, Buffer that flattens incoming arrays and allows consumers to take arbitrary-sized chunks. Improvements and suggestions welcome. Fork my gist at https://gist.github.com/1648579.

Circular Buffer

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type CircularBuffer<'a> (bufferSize: int) =
    do if bufferSize <= 0 then invalidArg "bufferSize" "The bufferSize must be greater than 0."

    let buffer = Array.zeroCreate<'a> bufferSize
    let mutable head = bufferSize - 1
    let mutable tail = 0
    let mutable length = 0

    let rec nextBuffer offset count =
        seq {
            let overflow = count + offset - bufferSize
            if overflow > 0 then
                yield (offset, bufferSize - offset)
                yield! nextBuffer 0 overflow
            else
                yield (offset, count)
        }

    member __.Dequeue(count) =
        if length = 0 then invalidOp "Queue exhausted."
        if count > length then invalidOp "Requested count is too large."

        let dequeued = Array.concat [| for o, c in nextBuffer tail count -> buffer.[o..o+c-1] |]

        tail <- (tail + count) % bufferSize
        length <- length - count
        dequeued

    member __.Enqueue(value: _[], offset, count) =
        if count > bufferSize then invalidOp "Requested count is too large."

        let mutable offset = offset

        head <- (head + 1) % bufferSize
        for x, y in nextBuffer head count do
            Array.blit value offset buffer x y
            offset <- offset + y

        if length = bufferSize then
            tail <- (tail + count) % bufferSize
        else
            let overflow = length + count - bufferSize
            if overflow > 0 then
                tail <- (tail + overflow) % bufferSize
            length <- min (length + count) bufferSize

    member __.Enqueue(value: _[]) =
        __.Enqueue(value, 0, value.Length)

    member __.Enqueue(value: _[], offset) =
        __.Enqueue(value, offset, value.Length - offset)

    member __.Enqueue(value: ArraySegment<_>) =
        __.Enqueue(value.Array, value.Offset, value.Count)

    member __.Enqueue(value) =
        __.Enqueue([|value|], 0, 1)

Usage

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let queue = CircularBuffer(5)

let stopwatch = Stopwatch.StartNew()

// Printing from a queue 1..5
queue.Enqueue(1)
queue.Enqueue(2)
queue.Enqueue(3)
queue.Enqueue(4)
queue.Enqueue(5)
Debug.Assert([|1;2;3;4;5|] = queue.Dequeue(5))

// Printing from a queue 1..8, twice
queue.Enqueue(1)
queue.Enqueue(2)
queue.Enqueue(3)
queue.Enqueue(4)
queue.Enqueue(5) // <---
queue.Enqueue(6)
queue.Enqueue(7)
queue.Enqueue(8)
queue.Enqueue(1)
queue.Enqueue(2) // <---
queue.Enqueue(3)
queue.Enqueue(4)
queue.Enqueue(5)
queue.Enqueue(6)
queue.Enqueue(7) // <---
queue.Enqueue(8)
Debug.Assert([|4;5;6;7;8|] = queue.Dequeue(5))

// Printing from a queue 1..5
queue.Enqueue(1)
queue.Enqueue(2)
queue.Enqueue(3)
queue.Enqueue(4)
queue.Enqueue(5)
Debug.Assert([|1;2;3|] = queue.Dequeue(3))

// Clear out the rest
queue.Dequeue(2)

// Printing from a queue 1..3
queue.Enqueue(1)
queue.Enqueue(2)
queue.Enqueue(3)
Debug.Assert([|1;2;3|] = queue.Dequeue(3))

// Printing from a queue 1..8 and dequeue 5, then enqueue 1..3 and dequeue 3
queue.Enqueue(1)
queue.Enqueue(2)
queue.Enqueue(3)
queue.Enqueue(4)
queue.Enqueue(5) // <---
queue.Enqueue(6)
queue.Enqueue(7)
queue.Enqueue(8)
Debug.Assert([|4;5;6;7;8|] = queue.Dequeue(5))
queue.Enqueue(1)
queue.Enqueue(2)
queue.Enqueue(3)
Debug.Assert([|1;2;3|] = queue.Dequeue(3))

printfn "Enqueue(value) tests passed in %d ms" stopwatch.ElapsedMilliseconds

stopwatch.Reset()
stopwatch.Start()

// Printing from a queue 1..5
queue.Enqueue([|1;2;3;4;5|])
Debug.Assert([|1;2;3;4;5|] = queue.Dequeue(5))

// Printing from a queue 1..8, twice
let error = ref Unchecked.defaultof<Exception>
try
  try
    queue.Enqueue([|1;2;3;4;5;6;7;8;1;2;3;4;5;6;7;8|])
  with e -> error := e
finally
  Debug.Assert(!error <> null)

queue.Enqueue([|1;2;3;4;5|])
queue.Enqueue([|6;7;8|])
queue.Enqueue([|1;2;3;4;5|])
queue.Enqueue([|6;7;8|])
Debug.Assert([|4;5;6;7;8|] = queue.Dequeue(5))

// Printing from a queue 1..5
queue.Enqueue([|1;2;3;4;5|])
Debug.Assert([|1;2;3|] = queue.Dequeue(3))

// Clear out the rest
queue.Dequeue(2)

// Printing from a queue 1..3
queue.Enqueue([|1;2;3|])
Debug.Assert([|1;2;3|] = queue.Dequeue(3))

// Printing from a queue 1..8 and dequeue 5, then enqueue 1..3 and dequeue 3
queue.Enqueue([|1;2;3;4;5|])
queue.Enqueue([|6;7;8|])
Debug.Assert([|4;5;6;7;8|] = queue.Dequeue(5))
queue.Enqueue([|1;2;3|])
Debug.Assert([|1;2;3|] = queue.Dequeue(3))

printfn "Enqueue(array) tests passed in %d ms" stopwatch.ElapsedMilliseconds

stopwatch.Reset()
stopwatch.Start()

// Consider a large array with various, incoming array segments.
let source =
    [| 1;2;3;4;5
       1;2;3;4;5;6;7;8;1;2;3;4;5;6;7;8
       1;2;3;4;5
       1;2;3
       1;2;3;4;5;6;7;8
       1;2;3 |]

let incoming =
    let generator =
        seq { yield ArraySegment<_>(source,0,5)
              yield ArraySegment<_>(source,5,5)
              yield ArraySegment<_>(source,10,3)
              yield ArraySegment<_>(source,13,5)
              yield ArraySegment<_>(source,18,3)
              yield ArraySegment<_>(source,21,5)
              yield ArraySegment<_>(source,26,3)
              yield ArraySegment<_>(source,29,5)
              yield ArraySegment<_>(source,34,3)
              yield ArraySegment<_>(source,37,3) } 
    in generator.GetEnumerator()

let enqueueNext() =
    incoming.MoveNext() |> ignore
    queue.Enqueue(incoming.Current)

// Printing from a queue 1..5
enqueueNext()
Debug.Assert([|1;2;3;4;5|] = queue.Dequeue(5))

// Printing from a queue 1..8, twice
enqueueNext()
enqueueNext()
enqueueNext()
enqueueNext()
Debug.Assert([|4;5;6;7;8|] = queue.Dequeue(5))

// Printing from a queue 1..5
enqueueNext()
Debug.Assert([|1;2;3|] = queue.Dequeue(3))

// Clear out the rest
queue.Dequeue(2)

// Printing from a queue 1..3
enqueueNext()
Debug.Assert([|1;2;3|] = queue.Dequeue(3))

// Printing from a queue 1..8 and dequeue 5, then enqueue 1..3 and dequeue 3
enqueueNext()
enqueueNext()
Debug.Assert([|4;5;6;7;8|] = queue.Dequeue(5))
enqueueNext()
Debug.Assert([|1;2;3|] = queue.Dequeue(3))

printfn "Enqueue(array) tests passed in %d ms" stopwatch.ElapsedMilliseconds
Multiple items
type CircularBuffer<'a> =
  new : bufferSize:int -> CircularBuffer<'a>
  member Dequeue : count:int -> 'a []
  member Enqueue : value:'a [] -> unit
  member Enqueue : value:ArraySegment<'a> -> unit
  member Enqueue : value:'a -> unit
  member Enqueue : value:'a [] * offset:int -> unit
  member Enqueue : value:'a [] * offset:int * count:int -> unit

Full name: Script.CircularBuffer<_>

--------------------
new : bufferSize:int -> CircularBuffer<'a>
val bufferSize : int
Multiple items
val int : value:'T -> int (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.Operators.int

--------------------
type int = int32

Full name: Microsoft.FSharp.Core.int

--------------------
type int<'Measure> = int

Full name: Microsoft.FSharp.Core.int<_>
val invalidArg : argumentName:string -> message:string -> 'T

Full name: Microsoft.FSharp.Core.Operators.invalidArg
val buffer : 'a []
type Array =
  member Clone : unit -> obj
  member CopyTo : array:Array * index:int -> unit + 1 overload
  member GetEnumerator : unit -> IEnumerator
  member GetLength : dimension:int -> int
  member GetLongLength : dimension:int -> int64
  member GetLowerBound : dimension:int -> int
  member GetUpperBound : dimension:int -> int
  member GetValue : [<ParamArray>] indices:int[] -> obj + 7 overloads
  member Initialize : unit -> unit
  member IsFixedSize : bool
  ...

Full name: System.Array
val zeroCreate : count:int -> 'T []

Full name: Microsoft.FSharp.Collections.Array.zeroCreate
val mutable head : int
val mutable tail : int
val mutable length : int
val nextBuffer : (int -> int -> seq<int * int>)
val offset : int
val count : int
Multiple items
val seq : sequence:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Core.Operators.seq

--------------------
type seq<'T> = Collections.Generic.IEnumerable<'T>

Full name: Microsoft.FSharp.Collections.seq<_>
val overflow : int
member CircularBuffer.Dequeue : count:int -> 'a []

Full name: Script.CircularBuffer`1.Dequeue
val invalidOp : message:string -> 'T

Full name: Microsoft.FSharp.Core.Operators.invalidOp
val dequeued : 'a []
val concat : arrays:seq<'T []> -> 'T []

Full name: Microsoft.FSharp.Collections.Array.concat
val o : int
val c : int
val __ : CircularBuffer<'a>
member CircularBuffer.Enqueue : value:'a [] * offset:int * count:int -> unit

Full name: Script.CircularBuffer`1.Enqueue
val value : 'a []
val mutable offset : int
val x : int
val y : int
val blit : source:'T [] -> sourceIndex:int -> target:'T [] -> targetIndex:int -> count:int -> unit

Full name: Microsoft.FSharp.Collections.Array.blit
val min : e1:'T -> e2:'T -> 'T (requires comparison)

Full name: Microsoft.FSharp.Core.Operators.min
member CircularBuffer.Enqueue : value:'a [] -> unit

Full name: Script.CircularBuffer`1.Enqueue
member CircularBuffer.Enqueue : value:'a [] -> unit
member CircularBuffer.Enqueue : value:ArraySegment<'a> -> unit
member CircularBuffer.Enqueue : value:'a -> unit
member CircularBuffer.Enqueue : value:'a [] * offset:int -> unit
member CircularBuffer.Enqueue : value:'a [] * offset:int * count:int -> unit
property Array.Length: int
member CircularBuffer.Enqueue : value:'a [] * offset:int -> unit

Full name: Script.CircularBuffer`1.Enqueue
member CircularBuffer.Enqueue : value:ArraySegment<'a> -> unit

Full name: Script.CircularBuffer`1.Enqueue
val value : ArraySegment<'a>
Multiple items
type ArraySegment<'T> =
  struct
    new : array:'T[] -> ArraySegment<'T> + 1 overload
    member Array : 'T[]
    member Count : int
    member Equals : obj:obj -> bool + 1 overload
    member GetHashCode : unit -> int
    member Offset : int
  end

Full name: System.ArraySegment<_>

--------------------
ArraySegment()
ArraySegment(array: 'T []) : unit
ArraySegment(array: 'T [], offset: int, count: int) : unit
property ArraySegment.Array: 'a []
property ArraySegment.Offset: int
property ArraySegment.Count: int
member CircularBuffer.Enqueue : value:'a -> unit

Full name: Script.CircularBuffer`1.Enqueue
val value : 'a
val queue : CircularBuffer<int>

Full name: Script.queue
val stopwatch : Stopwatch

Full name: Script.stopwatch
Multiple items
type Stopwatch =
  new : unit -> Stopwatch
  member Elapsed : TimeSpan
  member ElapsedMilliseconds : int64
  member ElapsedTicks : int64
  member IsRunning : bool
  member Reset : unit -> unit
  member Restart : unit -> unit
  member Start : unit -> unit
  member Stop : unit -> unit
  static val Frequency : int64
  ...

Full name: System.Diagnostics.Stopwatch

--------------------
Stopwatch() : unit
Stopwatch.StartNew() : Stopwatch
type Debug =
  static member Assert : condition:bool -> unit + 3 overloads
  static member AutoFlush : bool with get, set
  static member Close : unit -> unit
  static member Fail : message:string -> unit + 1 overload
  static member Flush : unit -> unit
  static member Indent : unit -> unit
  static member IndentLevel : int with get, set
  static member IndentSize : int with get, set
  static member Listeners : TraceListenerCollection
  static member Print : message:string -> unit + 1 overload
  ...

Full name: System.Diagnostics.Debug
Debug.Assert(condition: bool) : unit
Debug.Assert(condition: bool, message: string) : unit
Debug.Assert(condition: bool, message: string, detailMessage: string) : unit
Debug.Assert(condition: bool, message: string, detailMessageFormat: string, [<ParamArray>] args: obj []) : unit
member CircularBuffer.Dequeue : count:int -> 'a []
val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn
property Stopwatch.ElapsedMilliseconds: int64
Stopwatch.Reset() : unit
Stopwatch.Start() : unit
val error : Exception ref

Full name: Script.error
Multiple items
val ref : value:'T -> 'T ref

Full name: Microsoft.FSharp.Core.Operators.ref

--------------------
type 'T ref = Ref<'T>

Full name: Microsoft.FSharp.Core.ref<_>
module Unchecked

from Microsoft.FSharp.Core.Operators
val defaultof<'T> : 'T

Full name: Microsoft.FSharp.Core.Operators.Unchecked.defaultof
Multiple items
type Exception =
  new : unit -> Exception + 2 overloads
  member Data : IDictionary
  member GetBaseException : unit -> Exception
  member GetObjectData : info:SerializationInfo * context:StreamingContext -> unit
  member GetType : unit -> Type
  member HelpLink : string with get, set
  member InnerException : Exception
  member Message : string
  member Source : string with get, set
  member StackTrace : string
  ...

Full name: System.Exception

--------------------
Exception() : unit
Exception(message: string) : unit
Exception(message: string, innerException: exn) : unit
val e : exn
val source : int []

Full name: Script.source
val incoming : Collections.Generic.IEnumerator<ArraySegment<int>>

Full name: Script.incoming
val generator : seq<ArraySegment<int>>
Collections.Generic.IEnumerable.GetEnumerator() : Collections.Generic.IEnumerator<ArraySegment<int>>
val enqueueNext : unit -> unit

Full name: Script.enqueueNext
Collections.IEnumerator.MoveNext() : bool
val ignore : value:'T -> unit

Full name: Microsoft.FSharp.Core.Operators.ignore
property Collections.Generic.IEnumerator.Current: ArraySegment<int>

More information

Link:http://fssnip.net/a8
Posted:12 years ago
Author:Ryan Riley
Tags: circular buffer , data structure , stream , pipeline

This web site is created using F# and Suave web server. It is hosted on Azure and the source code is on GitHub. Contributions are welcome!

The first version of fssnip.net has been created by @tomaspetricek back in 2010. This web site is a new, open-source and contribution-friendly version.