Async.Catch<'T> 方法 (F#)
创建执行指定计算的异步计算。 如果此计算成功完成,则此方法返回包含返回值的 Choice1Of2。 如果此计算在完成之前引发异常,则返回包含引发的异常的 Choice2Of2。
命名空间/模块路径: Microsoft.FSharp.Control
程序集:FSharp.Core(在 FSharp.Core.dll 中)
// Signature:
static member Catch : Async<'T> -> Async<Choice<'T,exn>>
// Usage:
Async.Catch (computation)
参数
computation
类型:Async<'T>返回类型 'T 的输入计算。
返回值
返回类型为 T 或异常 选项 的计算。
示例
以下代码示例演示如何使用 Async.Catch 运行可能引发异常的异步计算。
open System
open System.IO
let writeToFile filename numBytes =
async {
use file = File.Create(filename)
printfn "Writing to file %s." filename
do! file.AsyncWrite(Array.zeroCreate<byte> numBytes)
}
let readFile filename numBytes =
async {
use file = File.OpenRead(filename)
printfn "Reading from file %s." filename
do! file.AsyncRead(numBytes) |> Async.Ignore
}
let filename = "BigFile.dat"
let numBytes = 100000000
let result1 = writeToFile filename numBytes
|> Async.Catch
|> Async.RunSynchronously
match result1 with
| Choice1Of2 _ -> printfn "Successfully wrote to file."; ()
| Choice2Of2 exn ->
printfn "Exception occurred writing to file %s: %s" filename exn.Message
// Start these next two operations asynchronously, forcing an exception due
// to trying to access the file twice simultaneously.
Async.Start(readFile filename numBytes)
let result2 = writeToFile filename numBytes
|> Async.Catch
|> Async.RunSynchronously
match result2 with
| Choice1Of2 buffer -> printfn "Successfully read from file."
| Choice2Of2 exn ->
printfn "Exception occurred reading from file %s: %s" filename (exn.Message)
平台
Windows 8,Windows 7,Windows server 2012中,Windows server 2008 R2
版本信息
F#核心库版本
支持:2.0,4.0,可移植