f# - 在异步工作流中捕获 HttpClient 超时

Question

我打电话 HttpClient通过 Async.AwaitTask ，从代理(MailboxProcessor)内部调用。我想在 HTTP 调用期间捕获错误，所以使用了 try...with在异步工作流中，但它完全错过了捕获客户端超时异常，然后导致代理崩溃。

最小复制:

#r "System.Net.Http"
open System
open System.Net.Http

let client = new HttpClient()
client.Timeout <- TimeSpan.FromSeconds(1.)
async {
    try
        let! content = Async.AwaitTask <| client.GetStringAsync("http://fake-response.appspot.com/?sleep=30")
        return content
    with ex ->
        // Does not catch client-side timeout exception
        return "Caught it!"
}
|> Async.RunSynchronously
// Throws System.OperationCanceledException: The operation was canceled

我可以通过使其完全同步来修复它，但更愿意保持整个堆栈异步，因为可能会并行运行很多这些:

#r "System.Net.Http"
open System
open System.Net.Http

let client = new HttpClient()
client.Timeout <- TimeSpan.FromSeconds(1.)
try
    Async.AwaitTask <| client.GetStringAsync("http://fake-response.appspot.com/?sleep=30")
    |> Async.RunSynchronously
with ex ->
    "Caught it!"
// Returns "Caught it!"

有没有有效的方法来捕捉 OperationCanceledException在异步上下文中？

Answer 1

这是因为 HttpClient.GetStringAsync任务将被取消，而不是失败并返回 TimeoutException ，从而促使异步机制触发其无法处理的取消延续。解决此问题的简单方法如下:

async {
    try
        let! content = 
            client.GetStringAsync("http://fake-response.appspot.com/?sleep=30")
                  .ContinueWith(fun (t:Task<string>) -> t.Result)
            |> Async.AwaitTask
        return content
    with ex ->
        // Does not catch client-side timeout exception
        return "Caught it!"
}