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Fix consume ValueTask backed by IValueTaskSource (#2108)
* Added AwaitHelper to properly wait for ValueTasks. * Adjust `AwaitHelper` to allow multiple threads to use it concurrently. * Changed AwaitHelper to static. * Add test case to make sure ValueTasks work properly with a race condition between `IsCompleted` and `OnCompleted`. Changed AwaitHelper to use `ManualResetEventSlim` instead of `Monitor.Wait`. * Make `ValueTaskWaiter.Wait` generic. * Compare types directly.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,108 @@ | ||
| using System; | ||
| using System.Linq; | ||
| using System.Reflection; | ||
| using System.Runtime.CompilerServices; | ||
| using System.Threading; | ||
| using System.Threading.Tasks; | ||
|
|
||
| namespace BenchmarkDotNet.Helpers | ||
| { | ||
| public static class AwaitHelper | ||
| { | ||
| private class ValueTaskWaiter | ||
| { | ||
| // We use thread static field so that each thread uses its own individual callback and reset event. | ||
| [ThreadStatic] | ||
| private static ValueTaskWaiter ts_current; | ||
| internal static ValueTaskWaiter Current => ts_current ??= new ValueTaskWaiter(); | ||
|
|
||
| // We cache the callback to prevent allocations for memory diagnoser. | ||
| private readonly Action awaiterCallback; | ||
| private readonly ManualResetEventSlim resetEvent; | ||
|
|
||
| private ValueTaskWaiter() | ||
| { | ||
| resetEvent = new (); | ||
| awaiterCallback = resetEvent.Set; | ||
| } | ||
|
|
||
| internal void Wait<TAwaiter>(TAwaiter awaiter) where TAwaiter : ICriticalNotifyCompletion | ||
| { | ||
| resetEvent.Reset(); | ||
| awaiter.UnsafeOnCompleted(awaiterCallback); | ||
|
|
||
| // The fastest way to wait for completion is to spin a bit before waiting on the event. This is the same logic that Task.GetAwaiter().GetResult() uses. | ||
| var spinner = new SpinWait(); | ||
| while (!resetEvent.IsSet) | ||
| { | ||
| if (spinner.NextSpinWillYield) | ||
| { | ||
| resetEvent.Wait(); | ||
| return; | ||
| } | ||
| spinner.SpinOnce(); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // we use GetAwaiter().GetResult() because it's fastest way to obtain the result in blocking way, | ||
| // and will eventually throw actual exception, not aggregated one | ||
| public static void GetResult(Task task) => task.GetAwaiter().GetResult(); | ||
|
|
||
| public static T GetResult<T>(Task<T> task) => task.GetAwaiter().GetResult(); | ||
|
|
||
| // ValueTask can be backed by an IValueTaskSource that only supports asynchronous awaits, | ||
| // so we have to hook up a callback instead of calling .GetAwaiter().GetResult() like we do for Task. | ||
| // The alternative is to convert it to Task using .AsTask(), but that causes allocations which we must avoid for memory diagnoser. | ||
| public static void GetResult(ValueTask task) | ||
| { | ||
| // Don't continue on the captured context, as that may result in a deadlock if the user runs this in-process. | ||
| var awaiter = task.ConfigureAwait(false).GetAwaiter(); | ||
| if (!awaiter.IsCompleted) | ||
| { | ||
| ValueTaskWaiter.Current.Wait(awaiter); | ||
| } | ||
| awaiter.GetResult(); | ||
| } | ||
|
|
||
| public static T GetResult<T>(ValueTask<T> task) | ||
| { | ||
| // Don't continue on the captured context, as that may result in a deadlock if the user runs this in-process. | ||
| var awaiter = task.ConfigureAwait(false).GetAwaiter(); | ||
| if (!awaiter.IsCompleted) | ||
| { | ||
| ValueTaskWaiter.Current.Wait(awaiter); | ||
| } | ||
| return awaiter.GetResult(); | ||
| } | ||
|
|
||
| internal static MethodInfo GetGetResultMethod(Type taskType) | ||
| { | ||
| if (!taskType.IsGenericType) | ||
| { | ||
| return typeof(AwaitHelper).GetMethod(nameof(AwaitHelper.GetResult), BindingFlags.Public | BindingFlags.Static, null, new Type[1] { taskType }, null); | ||
| } | ||
|
|
||
| Type compareType = taskType.GetGenericTypeDefinition() == typeof(ValueTask<>) ? typeof(ValueTask<>) | ||
| : typeof(Task).IsAssignableFrom(taskType.GetGenericTypeDefinition()) ? typeof(Task<>) | ||
| : null; | ||
| if (compareType == null) | ||
| { | ||
| return null; | ||
| } | ||
| var resultType = taskType | ||
| .GetMethod(nameof(Task.GetAwaiter), BindingFlags.Public | BindingFlags.Instance) | ||
| .ReturnType | ||
| .GetMethod(nameof(TaskAwaiter.GetResult), BindingFlags.Public | BindingFlags.Instance) | ||
| .ReturnType; | ||
| return typeof(AwaitHelper).GetMethods(BindingFlags.Public | BindingFlags.Static) | ||
| .First(m => | ||
| { | ||
| if (m.Name != nameof(AwaitHelper.GetResult)) return false; | ||
| Type paramType = m.GetParameters().First().ParameterType; | ||
| return paramType.IsGenericType && paramType.GetGenericTypeDefinition() == compareType; | ||
| }) | ||
| .MakeGenericMethod(new[] { resultType }); | ||
| } | ||
| } | ||
| } |
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