Async.AwaitWaitHandle Method (F#)

Article
07/11/2012

Creates an asynchronous computation that will wait for the supplied WaitHandle.

Namespace/Module Path: Microsoft.FSharp.Control

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

// Signature:
static member AwaitWaitHandle : WaitHandle * ?int -> Async<bool>

// Usage:
Async.AwaitWaitHandle (waitHandle)
Async.AwaitWaitHandle (waitHandle, millisecondsTimeout = millisecondsTimeout)

Parameters

waitHandle
Type: WaitHandle

The wait handle that can be signaled.
millisecondsTimeout
Type: int

The timeout value in milliseconds. If no timeout value is provided, the default value is -1, which corresponds to ystem.Threading.Timeout.Infinite.

Return Value

An asynchronous computation that waits on the given WaitHandle object.

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.AwaitWaitHandle to set up a computation to run when another asynchronous operation is completed, as indicated by a wait handle.

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 the waitHandle to wait for the write operation 
// to be completed before reading. 
let readFile filename waitHandle count = 
    async {
        let! returnValue = Async.AwaitWaitHandle(waitHandle)
        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.AsyncWaitHandle count
                   |> Async.RunSynchronously

Output

Writing to file BigFile.dat.
Reading from file BigFile.dat.

Platforms

Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2

Version Information

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

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