Timeout for async task

Question

My application currently executes Adobe Illustrator with some command. Waits when result file appears in some exact folder (with async function) and does something with file when it's ready.

But the problem is, sometimes Adobe Illustrator fails and app keeps waiting. In such cases I can't figure out, how can I apply timeout mechanism to kill Adobe Illustrator and skip current process.

Here is the code:

...
await WhenFileCreated(result_file_name);
if (File.Exists(result_file_name))
{
...


public static Task WhenFileCreated(string path)
{
    if (File.Exists(path))
        return Task.FromResult(true);

    var tcs = new TaskCompletionSource<bool>();
    FileSystemWatcher watcher = new FileSystemWatcher(Path.GetDirectoryName(path));

    FileSystemEventHandler createdHandler = null;
    RenamedEventHandler renamedHandler = null;
    createdHandler = (s, e) =>
    {
        if (e.Name == Path.GetFileName(path))
        {
            tcs.TrySetResult(true);
            watcher.Created -= createdHandler;
            watcher.Dispose();
        }
    };

    renamedHandler = (s, e) =>
    {
        if (e.Name == Path.GetFileName(path))
        {
            tcs.TrySetResult(true);
            watcher.Renamed -= renamedHandler;
            watcher.Dispose();
        }
    };

    watcher.Created += createdHandler;
    watcher.Renamed += renamedHandler;

    watcher.EnableRaisingEvents = true;

    return tcs.Task;
}

How to apply timeout to this? Any suggestions?

Possible duplicate of: https://stackoverflow.com/questions/25985416/how-can-i-set-a-timeout-for-an-async-function-that-doesnt-accept-a-cancellation and https://stackoverflow.com/questions/10134310/how-to-cancel-a-task-in-await — sɐunıɔןɐqɐp, Apr 26 '18 at 12:02
how are you starting adobe (i assume using a process object)...does it return a non-zero exit code on failure?....this also seems like an odd use a filesystemwatcher which is already based on an event model — Ctznkane525, Apr 26 '18 at 12:02

spender · Answer 1 · 2018-04-26T13:25:11.830

9

The simplest way would be to race a Task.Delay against the actual task:

await Task.WhenAny(WhenFileCreated(result_file_name), 
                   Task.Delay(TimeSpan.FromSeconds(5));

A better way would be implement cancellation in your async method

public static Task WhenFileCreated(string path, 
                                   CancellationToken ct = 
                                       default(CancellationToken))
{
     //...
     var tcs = new TaskCompletionSource<bool>();
     ct.Register(() => tcs.TrySetCanceled())
     //...
}

...and then pass in a cancellation token with a timeout:

using(var cts = new CancellationTokenSource(5000))
{
    try
    {
        await WhenFileCreated(string path, cts.Token);
    }
    catch(TaskCanceledException)
    {
        //...
    }
}

edited Apr 26 '18 at 13:25

answered Apr 26 '18 at 12:07

spender

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why is the cancellation way better than the simple WhenAny task ? – user1735921 Aug 29 '22 at 14:38
Also it is not working, my task is not getting cancelled using this... – user1735921 Aug 29 '22 at 14:47
What happens (exceptions, etc.) with `Task.WhenAny` solution if `WhenFileCreated` is executing for example 30 seconds ? – sabiland Dec 02 '22 at 14:28

score 0 · Answer 2 · answered Apr 26 '18 at 12:04

Try modifying your code to set this timeout for example.

var tcs = new TaskCompletionSource<TestResult>();

const int timeoutMs = 20000;
var ct = new CancellationTokenSource(timeoutMs);
ct.Token.Register(() => tcs.TrySetCanceled(), useSynchronizationContext: false);

More details you can find in: Timeout an async method implemented with TaskCompletionSource

Timeout for async task

2 Answers2