Async.AwaitIAsyncResult Method (F#)

Article
2013-02-04

Creates an asynchronous computation that will wait on the IAsyncResult.

Namespace/Module Path: Microsoft.FSharp.Control

Assembly: FSharp.Core (in FSharp.Core.dll)

// Signature:
static member AwaitIAsyncResult : IAsyncResult * ?int -> Async<bool>

// Usage:
Async.AwaitIAsyncResult (iar)
Async.AwaitIAsyncResult (iar, millisecondsTimeout = millisecondsTimeout)

Parameters

iar
Type: IAsyncResult

The IAsyncResult to wait on.
millisecondsTimeout
Type: int

The timeout value in milliseconds. If one is not provided then the default value of -1 corresponding to Infinite.

Return Value

An asynchronous computation that waits on the given IAsyncResult.

Remarks

The computation returns true if the handle indicated a result within the given timeout.

Example

The following code example illustrates how to use Async.AwaitIAsyncResult to set up and execute a computation that is triggered when a previous .NET Framework asynchronous operation that produces an IAsyncResult finishes. In this case, the call to AwaitIAsyncResult causes the operation to wait for a file write operation to be completed before opening the file for reading.

open System.IO

let streamWriter1 = File.CreateText("test1.txt")
let count = 10000000
let buffer = Array.init count (fun index -> byte (index % 256)) 

printfn "Writing to file test1.txt."
let asyncResult = streamWriter1.BaseStream.BeginWrite(buffer, 0, count, null, null)

// Read a file, but use AwaitIAsyncResult to wait for the write operation
// to be completed before reading.
let readFile filename asyncResult count = 
    async {
        let! returnValue = Async.AwaitIAsyncResult(asyncResult)
        printfn "Reading from file test1.txt."
        // Close the file.
        streamWriter1.Close()
        // Now open the same file for reading.
        let streamReader1 = File.OpenText(filename)
        let! newBuffer = streamReader1.BaseStream.AsyncRead(count)
        return newBuffer
    }

let bufferResult = readFile "test1.txt" asyncResult count
                   |> Async.RunSynchronously

Platforms

Windows 7, Windows Vista SP2, Windows XP SP3, Windows XP x64 SP2, Windows Server 2008 R2, Windows Server 2008 SP2, Windows Server 2003 SP2

Version Information

F# Runtime

Supported in: 2.0, 4.0

Silverlight

Supported in: 3

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