diff options
Diffstat (limited to 'src/mscorlib/src/System/Runtime/CompilerServices/YieldAwaitable.cs')
| -rw-r--r-- | src/mscorlib/src/System/Runtime/CompilerServices/YieldAwaitable.cs | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/src/mscorlib/src/System/Runtime/CompilerServices/YieldAwaitable.cs b/src/mscorlib/src/System/Runtime/CompilerServices/YieldAwaitable.cs new file mode 100644 index 0000000000..64609875ff --- /dev/null +++ b/src/mscorlib/src/System/Runtime/CompilerServices/YieldAwaitable.cs @@ -0,0 +1,167 @@ +// Copyright (c) Microsoft. All rights reserved. +// Licensed under the MIT license. See LICENSE file in the project root for full license information. + +// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +// +// +// +// Compiler-targeted type for switching back into the current execution context, e.g. +// +// await Task.Yield(); +// ===================== +// var $awaiter = Task.Yield().GetAwaiter(); +// if (!$awaiter.IsCompleted) +// { +// $builder.AwaitUnsafeOnCompleted(ref $awaiter, ref this); +// return; +// Label: +// } +// $awaiter.GetResult(); +// +// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- + +using System; +using System.Security; +using System.Diagnostics; +using System.Diagnostics.Contracts; +using System.Diagnostics.Tracing; +using System.Threading; +using System.Threading.Tasks; +using System.Security.Permissions; + +namespace System.Runtime.CompilerServices +{ + // NOTE: YieldAwaitable currently has no state; while developers are encouraged to use Task.Yield() to produce one, + // no validation is performed to ensure that the developer isn't doing "await new YieldAwaitable()". Such validation + // would require additional, useless state to be stored, and as this is a type in the CompilerServices namespace, and + // as the above example isn't harmful, we take the cheaper approach of not validating anything. + + /// <summary>Provides an awaitable context for switching into a target environment.</summary> + /// <remarks>This type is intended for compiler use only.</remarks> + public struct YieldAwaitable + { + /// <summary>Gets an awaiter for this <see cref="YieldAwaitable"/>.</summary> + /// <returns>An awaiter for this awaitable.</returns> + /// <remarks>This method is intended for compiler user rather than use directly in code.</remarks> + public YieldAwaiter GetAwaiter() { return new YieldAwaiter(); } + + /// <summary>Provides an awaiter that switches into a target environment.</summary> + /// <remarks>This type is intended for compiler use only.</remarks> + [HostProtection(Synchronization = true, ExternalThreading = true)] + public struct YieldAwaiter : ICriticalNotifyCompletion + { + /// <summary>Gets whether a yield is not required.</summary> + /// <remarks>This property is intended for compiler user rather than use directly in code.</remarks> + public bool IsCompleted { get { return false; } } // yielding is always required for YieldAwaiter, hence false + + /// <summary>Posts the <paramref name="continuation"/> back to the current context.</summary> + /// <param name="continuation">The action to invoke asynchronously.</param> + /// <exception cref="System.ArgumentNullException">The <paramref name="continuation"/> argument is null (Nothing in Visual Basic).</exception> + [SecuritySafeCritical] + public void OnCompleted(Action continuation) + { + QueueContinuation(continuation, flowContext: true); + } + + /// <summary>Posts the <paramref name="continuation"/> back to the current context.</summary> + /// <param name="continuation">The action to invoke asynchronously.</param> + /// <exception cref="System.ArgumentNullException">The <paramref name="continuation"/> argument is null (Nothing in Visual Basic).</exception> + [SecurityCritical] + public void UnsafeOnCompleted(Action continuation) + { + QueueContinuation(continuation, flowContext: false); + } + + /// <summary>Posts the <paramref name="continuation"/> back to the current context.</summary> + /// <param name="continuation">The action to invoke asynchronously.</param> + /// <param name="flowContext">true to flow ExecutionContext; false if flowing is not required.</param> + /// <exception cref="System.ArgumentNullException">The <paramref name="continuation"/> argument is null (Nothing in Visual Basic).</exception> + [SecurityCritical] + private static void QueueContinuation(Action continuation, bool flowContext) + { + // Validate arguments + if (continuation == null) throw new ArgumentNullException("continuation"); + Contract.EndContractBlock(); + + if (TplEtwProvider.Log.IsEnabled()) + { + continuation = OutputCorrelationEtwEvent(continuation); + } + // Get the current SynchronizationContext, and if there is one, + // post the continuation to it. However, treat the base type + // as if there wasn't a SynchronizationContext, since that's what it + // logically represents. + var syncCtx = SynchronizationContext.CurrentNoFlow; + if (syncCtx != null && syncCtx.GetType() != typeof(SynchronizationContext)) + { + syncCtx.Post(s_sendOrPostCallbackRunAction, continuation); + } + else + { + // If we're targeting the default scheduler, queue to the thread pool, so that we go into the global + // queue. As we're going into the global queue, we might as well use QUWI, which for the global queue is + // just a tad faster than task, due to a smaller object getting allocated and less work on the execution path. + TaskScheduler scheduler = TaskScheduler.Current; + if (scheduler == TaskScheduler.Default) + { + if (flowContext) + { + ThreadPool.QueueUserWorkItem(s_waitCallbackRunAction, continuation); + } + else + { + ThreadPool.UnsafeQueueUserWorkItem(s_waitCallbackRunAction, continuation); + } + } + // We're targeting a custom scheduler, so queue a task. + else + { + Task.Factory.StartNew(continuation, default(CancellationToken), TaskCreationOptions.PreferFairness, scheduler); + } + } + } + + private static Action OutputCorrelationEtwEvent(Action continuation) + { + int continuationId = Task.NewId(); + Task currentTask = Task.InternalCurrent; + // fire the correlation ETW event + TplEtwProvider.Log.AwaitTaskContinuationScheduled(TaskScheduler.Current.Id, (currentTask != null) ? currentTask.Id : 0, continuationId); + + return AsyncMethodBuilderCore.CreateContinuationWrapper(continuation, () => + { + var etwLog = TplEtwProvider.Log; + etwLog.TaskWaitContinuationStarted(continuationId); + + // ETW event for Task Wait End. + Guid prevActivityId = new Guid(); + // Ensure the continuation runs under the correlated activity ID generated above + if (etwLog.TasksSetActivityIds) + EventSource.SetCurrentThreadActivityId(TplEtwProvider.CreateGuidForTaskID(continuationId), out prevActivityId); + + // Invoke the original continuation provided to OnCompleted. + continuation(); + // Restore activity ID + + if (etwLog.TasksSetActivityIds) + EventSource.SetCurrentThreadActivityId(prevActivityId); + + etwLog.TaskWaitContinuationComplete(continuationId); + }); + + } + + /// <summary>WaitCallback that invokes the Action supplied as object state.</summary> + private static readonly WaitCallback s_waitCallbackRunAction = RunAction; + /// <summary>SendOrPostCallback that invokes the Action supplied as object state.</summary> + private static readonly SendOrPostCallback s_sendOrPostCallbackRunAction = RunAction; + + /// <summary>Runs an Action delegate provided as state.</summary> + /// <param name="state">The Action delegate to invoke.</param> + private static void RunAction(object state) { ((Action)state)(); } + + /// <summary>Ends the await operation.</summary> + public void GetResult() {} // Nop. It exists purely because the compiler pattern demands it. + } + } +} |