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Diffstat (limited to 'src/mscorlib/src/System/Threading/Tasks/BeginEndAwaitableAdapter.cs')
| -rw-r--r-- | src/mscorlib/src/System/Threading/Tasks/BeginEndAwaitableAdapter.cs | 157 |
1 files changed, 0 insertions, 157 deletions
diff --git a/src/mscorlib/src/System/Threading/Tasks/BeginEndAwaitableAdapter.cs b/src/mscorlib/src/System/Threading/Tasks/BeginEndAwaitableAdapter.cs deleted file mode 100644 index 71eb787c5e..0000000000 --- a/src/mscorlib/src/System/Threading/Tasks/BeginEndAwaitableAdapter.cs +++ /dev/null @@ -1,157 +0,0 @@ -// Licensed to the .NET Foundation under one or more agreements. -// The .NET Foundation licenses this file to you under the MIT license. -// See the LICENSE file in the project root for more information. - -using System; -using System.Diagnostics; -using System.Diagnostics.Contracts; -using System.IO; -using System.Runtime.CompilerServices; -using System.Security; -using System.Threading; -using System.Threading.Tasks; - -namespace System.Threading.Tasks { - -/// <summary> -/// Provides an adapter to make Begin/End pairs awaitable. -/// In general, Task.Factory.FromAsync should be used for this purpose. -/// However, for cases where absolute minimal overhead is required, this type -/// may be used to making APM pairs awaitable while minimizing overhead. -/// (APM = Asynchronous Programming Model or the Begin/End pattern.) -/// </summary> -/// <remarks> -/// This instance may be reused repeatedly. However, it must only be used -/// by a single APM invocation at a time. It's state will automatically be reset -/// when the await completes. -/// </remarks> -/// <example> -/// Usage sample: -/// <code> -/// static async Task CopyStreamAsync(Stream source, Stream dest) { -/// -/// BeginEndAwaitableAdapter adapter = new BeginEndAwaitableAdapter(); -/// Byte[] buffer = new Byte[0x1000]; -/// -/// while (true) { -/// -/// source.BeginRead(buffer, 0, buffer.Length, BeginEndAwaitableAdapter.Callback, adapter); -/// Int32 numRead = source.EndRead(await adapter); -/// if (numRead == 0) -/// break; -/// -/// dest.BeginWrite(buffer, 0, numRead, BeginEndAwaitableAdapter.Callback, adapter); -/// dest.EndWrite(await adapter); -/// } -/// } -/// </code> -/// </example> -internal sealed class BeginEndAwaitableAdapter : ICriticalNotifyCompletion { - - /// <summary>A sentinel marker used to communicate between OnCompleted and the APM callback - /// that the callback has already run, and thus OnCompleted needs to execute the callback.</summary> - private readonly static Action CALLBACK_RAN = () => { }; - - /// <summary>The IAsyncResult for the APM operation.</summary> - private IAsyncResult _asyncResult; - - /// <summary>The continuation delegate provided to the awaiter.</summary> - private Action _continuation; - - - /// <summary>A callback to be passed as the AsyncCallback to an APM pair. - /// It expects that an BeginEndAwaitableAdapter instance was supplied to the APM Begin method as the object state.</summary> - public readonly static AsyncCallback Callback = (asyncResult) => { - - Debug.Assert(asyncResult != null); - Debug.Assert(asyncResult.IsCompleted); - Debug.Assert(asyncResult.AsyncState is BeginEndAwaitableAdapter); - - // Get the adapter object supplied as the "object state" to the Begin method - BeginEndAwaitableAdapter adapter = (BeginEndAwaitableAdapter) asyncResult.AsyncState; - - // Store the IAsyncResult into it so that it's available to the awaiter - adapter._asyncResult = asyncResult; - - // If the _continuation has already been set to the actual continuation by OnCompleted, then invoke the continuation. - // Set _continuation to the CALLBACK_RAN sentinel so that IsCompleted returns true and OnCompleted sees the sentinel - // and knows to invoke the callback. - // Due to some known incorrect implementations of IAsyncResult in the Framework where CompletedSynchronously is lazily - // set to true if it is first invoked after IsCompleted is true, we cannot rely here on CompletedSynchronously for - // synchronization between the caller and the callback, and thus do not use CompletedSynchronously at all. - Action continuation = Interlocked.Exchange(ref adapter._continuation, CALLBACK_RAN); - if (continuation != null) { - - Debug.Assert(continuation != CALLBACK_RAN); - continuation(); - } - }; - - - /// <summary>Gets an awaiter.</summary> - /// <returns>Returns itself as the awaiter.</returns> - public BeginEndAwaitableAdapter GetAwaiter() { - - return this; - } - - - /// <summary>Gets whether the awaited APM operation completed.</summary> - public bool IsCompleted { - get { - - // We are completed if the callback was called and it set the continuation to the CALLBACK_RAN sentinel. - // If the operation completes asynchronously, there's still a chance we'll see CALLBACK_RAN here, in which - // case we're still good to keep running synchronously. - return (_continuation == CALLBACK_RAN); - } - } - - /// <summary>Schedules the continuation to run when the operation completes.</summary> - /// <param name="continuation">The continuation.</param> - public void UnsafeOnCompleted(Action continuation) { - - Debug.Assert(continuation != null); - OnCompleted(continuation); - } - - - /// <summary>Schedules the continuation to run when the operation completes.</summary> - /// <param name="continuation">The continuation.</param> - public void OnCompleted(Action continuation) { - - Debug.Assert(continuation != null); - - // If the continuation field is null, then set it to be the target continuation - // so that when the operation completes, it'll invoke the continuation. If it's non-null, - // it was already set to the CALLBACK_RAN-sentinel by the Callback, in which case we hit a very rare race condition - // where the operation didn't complete synchronously but completed asynchronously between our - // calls to IsCompleted and OnCompleted... in that case, just schedule a task to run the continuation. - if (_continuation == CALLBACK_RAN - || Interlocked.CompareExchange(ref _continuation, continuation, null) == CALLBACK_RAN) { - - Task.Run(continuation); // must run async at this point, or else we'd risk stack diving - } - } - - - /// <summary>Gets the IAsyncResult for the APM operation after the operation completes, and then resets the adapter.</summary> - /// <returns>The IAsyncResult for the operation.</returns> - public IAsyncResult GetResult() { - - Debug.Assert(_asyncResult != null && _asyncResult.IsCompleted); - - // Get the IAsyncResult - IAsyncResult result = _asyncResult; - - // Reset the adapter - _asyncResult = null; - _continuation = null; - - // Return the result - return result; - } - -} // class BeginEndAwaitableAdapter - -} // namespace |