问题
I am struggling with the following:
I have a system that has its main flow and has two background threads that can be started and stopped, but they're generally very long running as they stop only during configuration changes.
I found that the cancellation token in F# gets checked at async points in the code. The worker threads do not perform any async operations; they are doing background work but nothing is asynchronous.
A simplified version looks like that:
let workerThread (someParameters) =
async {
while true do
setup some event driven system that has a callback when work is finished
on callback, signal
waitHandle.WaitOne()
}
and it gets started like this:
Async.StartAsTask(workerThread parameter, cancellationToken = cancellationSource.Token)
Since there is absolutely nothing async in the system, the cancellation token will never be checked and, besides, I need to be able to manually check it in the event driven systems that keep getting set up by the two worker threads.
How can this be done? In C# the token is passed directly and I can check it whenever I feel like.
回答1:
F# propagates cancellation token to the task which is created, but if worker function is blocked while waiting for a handle it cannot check the cancellation token. To solve this issue you should wait for the cancellation token wait handle as well:
let workerThread () =
async {
let! token = Async.CancellationToken // this way you can get cancellation token
while true do
// whatever
WaitHandle.WaitAny([| waitHandle; token.WaitHandle |]) |> ignore
}
来源:https://stackoverflow.com/questions/65637876/cancellation-token-in-f-threads