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PODoes Async.StartChild have a memory leak?
 

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  1. PODoes Async.StartChild have a memory leak?
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    <p>When I run the following test (built with F#2.0) I get OutOfMemoryException. It takes about 5 min to reach exception on my system (i7-920 6gb ram if it was running as x86 process), but in any case we can see how memory is growing in task manager.</p> <pre><code>module start_child_test open System open System.Diagnostics open System.Threading open System.Threading.Tasks let cnt = ref 0 let sw = Stopwatch.StartNew() Async.RunSynchronously(async{ while true do let! x = Async.StartChild(async{ if (Interlocked.Increment(cnt) % 100000) = 0 then if sw.ElapsedMilliseconds &gt; 0L then printfn "ops per sec = %d" (100000L*1000L / sw.ElapsedMilliseconds) else printfn "ops per sec = INF" sw.Restart() GC.Collect() }) do! x }) printfn "done...." </code></pre> <p>I don't see nothing wrong with this code, and don't see any reasons for memory growing. I made alternate implementation to make sure my arguments are valid:</p> <pre><code>module start_child_fix open System open System.Collections open System.Collections.Generic open System.Threading open System.Threading.Tasks type IAsyncCallbacks&lt;'T&gt; = interface abstract member OnSuccess: result:'T -&gt; unit abstract member OnError: error:Exception -&gt; unit abstract member OnCancel: error:OperationCanceledException -&gt; unit end type internal AsyncResult&lt;'T&gt; = | Succeeded of 'T | Failed of Exception | Canceled of OperationCanceledException type internal AsyncGate&lt;'T&gt; = | Completed of AsyncResult&lt;'T&gt; | Subscribed of IAsyncCallbacks&lt;'T&gt; | Started | Notified type Async with static member StartChildEx (comp:Async&lt;'TRes&gt;) = async{ let! ct = Async.CancellationToken let gate = ref AsyncGate.Started let CompleteWith(result:AsyncResult&lt;'T&gt;, callbacks:IAsyncCallbacks&lt;'T&gt;) = if Interlocked.Exchange(gate, Notified) &lt;&gt; Notified then match result with | Succeeded v -&gt; callbacks.OnSuccess(v) | Failed e -&gt; callbacks.OnError(e) | Canceled e -&gt; callbacks.OnCancel(e) let ProcessResults (result:AsyncResult&lt;'TRes&gt;) = let t = Interlocked.CompareExchange&lt;AsyncGate&lt;'TRes&gt;&gt;(gate, AsyncGate.Completed(result), AsyncGate.Started) match t with | Subscribed callbacks -&gt; CompleteWith(result, callbacks) | _ -&gt; () let Subscribe (success, error, cancel) = let callbacks = { new IAsyncCallbacks&lt;'TRes&gt; with member this.OnSuccess v = success v member this.OnError e = error e member this.OnCancel e = cancel e } let t = Interlocked.CompareExchange&lt;AsyncGate&lt;'TRes&gt;&gt;(gate, AsyncGate.Subscribed(callbacks), AsyncGate.Started) match t with | AsyncGate.Completed result -&gt; CompleteWith(result, callbacks) | _ -&gt; () Async.StartWithContinuations( computation = comp, continuation = (fun v -&gt; ProcessResults(AsyncResult.Succeeded(v))), exceptionContinuation = (fun e -&gt; ProcessResults(AsyncResult.Failed(e))), cancellationContinuation = (fun e -&gt; ProcessResults(AsyncResult.Canceled(e))), cancellationToken = ct ) return Async.FromContinuations( fun (success, error, cancel) -&gt; Subscribe(success, error, cancel) ) } </code></pre> <p>For this test it works well without any considerably memory consumption. Unfortunately I'm not much experienced in F# and have doubts if I miss some things. In case if it is bug how can I report it to F# team?</p>
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