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Diffstat (limited to 'src/mscorlib/shared/System/Progress.cs')
-rw-r--r-- | src/mscorlib/shared/System/Progress.cs | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/src/mscorlib/shared/System/Progress.cs b/src/mscorlib/shared/System/Progress.cs new file mode 100644 index 0000000000..755e7719fe --- /dev/null +++ b/src/mscorlib/shared/System/Progress.cs @@ -0,0 +1,105 @@ +// 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.Threading; +using System.Diagnostics; + +namespace System +{ + /// <summary> + /// Provides an IProgress{T} that invokes callbacks for each reported progress value. + /// </summary> + /// <typeparam name="T">Specifies the type of the progress report value.</typeparam> + /// <remarks> + /// Any handler provided to the constructor or event handlers registered with + /// the <see cref="ProgressChanged"/> event are invoked through a + /// <see cref="System.Threading.SynchronizationContext"/> instance captured + /// when the instance is constructed. If there is no current SynchronizationContext + /// at the time of construction, the callbacks will be invoked on the ThreadPool. + /// </remarks> + public class Progress<T> : IProgress<T> + { + /// <summary>The synchronization context captured upon construction. This will never be null.</summary> + private readonly SynchronizationContext _synchronizationContext; + /// <summary>The handler specified to the constructor. This may be null.</summary> + private readonly Action<T> _handler; + /// <summary>A cached delegate used to post invocation to the synchronization context.</summary> + private readonly SendOrPostCallback _invokeHandlers; + + /// <summary>Initializes the <see cref="Progress{T}"/>.</summary> + public Progress() + { + // Capture the current synchronization context. + // If there is no current context, we use a default instance targeting the ThreadPool. + _synchronizationContext = SynchronizationContext.Current ?? ProgressStatics.DefaultContext; + Debug.Assert(_synchronizationContext != null); + _invokeHandlers = new SendOrPostCallback(InvokeHandlers); + } + + /// <summary>Initializes the <see cref="Progress{T}"/> with the specified callback.</summary> + /// <param name="handler"> + /// A handler to invoke for each reported progress value. This handler will be invoked + /// in addition to any delegates registered with the <see cref="ProgressChanged"/> event. + /// Depending on the <see cref="System.Threading.SynchronizationContext"/> instance captured by + /// the <see cref="Progress"/> at construction, it's possible that this handler instance + /// could be invoked concurrently with itself. + /// </param> + /// <exception cref="System.ArgumentNullException">The <paramref name="handler"/> is null (Nothing in Visual Basic).</exception> + public Progress(Action<T> handler) : this() + { + if (handler == null) throw new ArgumentNullException(nameof(handler)); + _handler = handler; + } + + /// <summary>Raised for each reported progress value.</summary> + /// <remarks> + /// Handlers registered with this event will be invoked on the + /// <see cref="System.Threading.SynchronizationContext"/> captured when the instance was constructed. + /// </remarks> + public event EventHandler<T> ProgressChanged; + + /// <summary>Reports a progress change.</summary> + /// <param name="value">The value of the updated progress.</param> + protected virtual void OnReport(T value) + { + // If there's no handler, don't bother going through the sync context. + // Inside the callback, we'll need to check again, in case + // an event handler is removed between now and then. + Action<T> handler = _handler; + EventHandler<T> changedEvent = ProgressChanged; + if (handler != null || changedEvent != null) + { + // Post the processing to the sync context. + // (If T is a value type, it will get boxed here.) + _synchronizationContext.Post(_invokeHandlers, value); + } + } + + /// <summary>Reports a progress change.</summary> + /// <param name="value">The value of the updated progress.</param> + void IProgress<T>.Report(T value) { OnReport(value); } + + /// <summary>Invokes the action and event callbacks.</summary> + /// <param name="state">The progress value.</param> + private void InvokeHandlers(object state) + { + T value = (T)state; + + Action<T> handler = _handler; + EventHandler<T> changedEvent = ProgressChanged; + + if (handler != null) handler(value); + if (changedEvent != null) changedEvent(this, value); + } + } + + /// <summary>Holds static values for <see cref="Progress{T}"/>.</summary> + /// <remarks>This avoids one static instance per type T.</remarks> + internal static class ProgressStatics + { + /// <summary>A default synchronization context that targets the ThreadPool.</summary> + internal static readonly SynchronizationContext DefaultContext = new SynchronizationContext(); + } +} |