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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
//
// ActionBlock.cs
//
//
// A target block that executes an action for each message.
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;
using System.Threading.Tasks.Dataflow.Internal;
namespace System.Threading.Tasks.Dataflow
{
/// <summary>Provides a dataflow block that invokes a provided <see cref="System.Action{T}"/> delegate for every data element received.</summary>
/// <typeparam name="TInput">Specifies the type of data operated on by this <see cref="ActionBlock{T}"/>.</typeparam>
[DebuggerDisplay("{DebuggerDisplayContent,nq}")]
[DebuggerTypeProxy(typeof(ActionBlock<>.DebugView))]
public sealed class ActionBlock<TInput> : ITargetBlock<TInput>, IDebuggerDisplay
{
/// <summary>The core implementation of this message block when in default mode.</summary>
private readonly TargetCore<TInput>? _defaultTarget;
/// <summary>The core implementation of this message block when in SPSC mode.</summary>
private readonly SpscTargetCore<TInput>? _spscTarget;
/// <summary>Initializes the <see cref="ActionBlock{T}"/> with the specified <see cref="System.Action{T}"/>.</summary>
/// <param name="action">The action to invoke with each data element received.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="action"/> is null (Nothing in Visual Basic).</exception>
public ActionBlock(Action<TInput> action) :
this((Delegate)action, ExecutionDataflowBlockOptions.Default)
{ }
/// <summary>Initializes the <see cref="ActionBlock{T}"/> with the specified <see cref="System.Action{T}"/> and <see cref="ExecutionDataflowBlockOptions"/>.</summary>
/// <param name="action">The action to invoke with each data element received.</param>
/// <param name="dataflowBlockOptions">The options with which to configure this <see cref="ActionBlock{T}"/>.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="action"/> is null (Nothing in Visual Basic).</exception>
/// <exception cref="System.ArgumentNullException">The <paramref name="dataflowBlockOptions"/> is null (Nothing in Visual Basic).</exception>
public ActionBlock(Action<TInput> action, ExecutionDataflowBlockOptions dataflowBlockOptions) :
this((Delegate)action, dataflowBlockOptions)
{ }
/// <summary>Initializes the <see cref="ActionBlock{T}"/> with the specified <see cref="System.Func{T,Task}"/>.</summary>
/// <param name="action">The action to invoke with each data element received.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="action"/> is null (Nothing in Visual Basic).</exception>
public ActionBlock(Func<TInput, Task> action) :
this((Delegate)action, ExecutionDataflowBlockOptions.Default)
{ }
/// <summary>Initializes the <see cref="ActionBlock{T}"/> with the specified <see cref="System.Func{T,Task}"/> and <see cref="ExecutionDataflowBlockOptions"/>.</summary>
/// <param name="action">The action to invoke with each data element received.</param>
/// <param name="dataflowBlockOptions">The options with which to configure this <see cref="ActionBlock{T}"/>.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="action"/> is null (Nothing in Visual Basic).</exception>
/// <exception cref="System.ArgumentNullException">The <paramref name="dataflowBlockOptions"/> is null (Nothing in Visual Basic).</exception>
public ActionBlock(Func<TInput, Task> action, ExecutionDataflowBlockOptions dataflowBlockOptions) :
this((Delegate)action, dataflowBlockOptions)
{ }
/// <summary>Initializes the <see cref="ActionBlock{T}"/> with the specified delegate and options.</summary>
/// <param name="action">The action to invoke with each data element received.</param>
/// <param name="dataflowBlockOptions">The options with which to configure this <see cref="ActionBlock{T}"/>.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="action"/> is null (Nothing in Visual Basic).</exception>
/// <exception cref="System.ArgumentNullException">The <paramref name="dataflowBlockOptions"/> is null (Nothing in Visual Basic).</exception>
private ActionBlock(Delegate action, ExecutionDataflowBlockOptions dataflowBlockOptions)
{
if (action is null)
{
throw new ArgumentNullException(nameof(action));
}
if (dataflowBlockOptions is null)
{
throw new ArgumentNullException(nameof(dataflowBlockOptions));
}
// Ensure we have options that can't be changed by the caller
dataflowBlockOptions = dataflowBlockOptions.DefaultOrClone();
// Based on the mode, initialize the target. If the user specifies SingleProducerConstrained,
// we'll try to employ an optimized mode under a limited set of circumstances.
var syncAction = action as Action<TInput>;
if (syncAction != null &&
dataflowBlockOptions.SingleProducerConstrained &&
dataflowBlockOptions.MaxDegreeOfParallelism == 1 &&
!dataflowBlockOptions.CancellationToken.CanBeCanceled &&
dataflowBlockOptions.BoundedCapacity == DataflowBlockOptions.Unbounded)
{
// Initialize the SPSC fast target to handle the bulk of the processing.
// The SpscTargetCore is only supported when BoundedCapacity, CancellationToken,
// and MaxDOP are all their default values. It's also only supported for sync
// delegates and not for async delegates.
_spscTarget = new SpscTargetCore<TInput>(this, syncAction, dataflowBlockOptions);
}
else
{
// Initialize the TargetCore which handles the bulk of the processing.
// The default target core can handle all options and delegate flavors.
if (syncAction != null) // sync
{
_defaultTarget = new TargetCore<TInput>(this,
messageWithId => ProcessMessage(syncAction, messageWithId),
null, dataflowBlockOptions, TargetCoreOptions.RepresentsBlockCompletion);
}
else // async
{
var asyncAction = action as Func<TInput, Task>;
Debug.Assert(asyncAction != null, "action is of incorrect delegate type");
_defaultTarget = new TargetCore<TInput>(this,
messageWithId => ProcessMessageWithTask(asyncAction, messageWithId),
null, dataflowBlockOptions, TargetCoreOptions.RepresentsBlockCompletion | TargetCoreOptions.UsesAsyncCompletion);
}
// Handle async cancellation requests by declining on the target
Common.WireCancellationToComplete(
dataflowBlockOptions.CancellationToken, Completion, static (state, _) => ((TargetCore<TInput>)state!).Complete(exception: null, dropPendingMessages: true), _defaultTarget);
}
DataflowEtwProvider etwLog = DataflowEtwProvider.Log;
if (etwLog.IsEnabled())
{
etwLog.DataflowBlockCreated(this, dataflowBlockOptions);
}
Debug.Assert((_spscTarget != null) ^ (_defaultTarget != null), "One and only one of the two targets must be non-null after construction");
}
/// <summary>Processes the message with a user-provided action.</summary>
/// <param name="action">The action to use to process the message.</param>
/// <param name="messageWithId">The message to be processed.</param>
private void ProcessMessage(Action<TInput> action, KeyValuePair<TInput, long> messageWithId)
{
Debug.Assert(_defaultTarget != null);
try
{
action(messageWithId.Key);
}
catch (Exception exc)
{
// If this exception represents cancellation, swallow it rather than shutting down the block.
if (!Common.IsCooperativeCancellation(exc)) throw;
}
finally
{
// We're done synchronously processing an element, so reduce the bounding count
// that was incrementing when this element was enqueued.
if (_defaultTarget.IsBounded) _defaultTarget.ChangeBoundingCount(-1);
}
}
/// <summary>Processes the message with a user-provided action that returns a task.</summary>
/// <param name="action">The action to use to process the message.</param>
/// <param name="messageWithId">The message to be processed.</param>
private void ProcessMessageWithTask(Func<TInput, Task> action, KeyValuePair<TInput, long> messageWithId)
{
Debug.Assert(action != null, "action needed for processing");
Debug.Assert(_defaultTarget != null);
// Run the action to get the task that represents the operation's completion
Task? task = null;
Exception? caughtException = null;
try
{
task = action(messageWithId.Key);
}
catch (Exception exc) { caughtException = exc; }
// If no task is available, we're done.
if (task == null)
{
// If we didn't get a task because an exception occurred,
// store it (if the exception was cancellation, just ignore it).
if (caughtException != null && !Common.IsCooperativeCancellation(caughtException))
{
Common.StoreDataflowMessageValueIntoExceptionData(caughtException, messageWithId.Key);
_defaultTarget.Complete(caughtException, dropPendingMessages: true, storeExceptionEvenIfAlreadyCompleting: true, unwrapInnerExceptions: false);
}
// Signal that we're done this async operation.
_defaultTarget.SignalOneAsyncMessageCompleted(boundingCountChange: -1);
return;
}
else if (task.IsCompleted)
{
AsyncCompleteProcessMessageWithTask(task);
}
else
{
// Otherwise, join with the asynchronous operation when it completes.
task.ContinueWith(static (completed, state) =>
{
((ActionBlock<TInput>)state!).AsyncCompleteProcessMessageWithTask(completed);
}, this, CancellationToken.None, Common.GetContinuationOptions(TaskContinuationOptions.ExecuteSynchronously), TaskScheduler.Default);
}
}
/// <summary>Completes the processing of an asynchronous message.</summary>
/// <param name="completed">The completed task.</param>
private void AsyncCompleteProcessMessageWithTask(Task completed)
{
Debug.Assert(completed != null, "Need completed task for processing");
Debug.Assert(completed.IsCompleted, "The task to be processed must be completed by now.");
Debug.Assert(_defaultTarget != null);
// If the task faulted, store its errors. We must add the exception before declining
// and signaling completion, as the exception is part of the operation, and the completion conditions
// depend on this.
if (completed.IsFaulted)
{
_defaultTarget.Complete(completed.Exception, dropPendingMessages: true, storeExceptionEvenIfAlreadyCompleting: true, unwrapInnerExceptions: true);
}
// Regardless of faults, note that we're done processing. There are
// no outputs to keep track of for action block, so we always decrement
// the bounding count here (the callee will handle checking whether
// we're actually in a bounded mode).
_defaultTarget.SignalOneAsyncMessageCompleted(boundingCountChange: -1);
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="Complete"]/*' />
public void Complete()
{
if (_defaultTarget != null)
{
_defaultTarget.Complete(exception: null, dropPendingMessages: false);
}
else
{
Debug.Assert(_spscTarget != null);
_spscTarget.Complete(exception: null);
}
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="Fault"]/*' />
void IDataflowBlock.Fault(Exception exception)
{
if (exception is null)
{
throw new ArgumentNullException(nameof(exception));
}
if (_defaultTarget != null)
{
_defaultTarget.Complete(exception, dropPendingMessages: true);
}
else
{
Debug.Assert(_spscTarget != null);
_spscTarget.Complete(exception);
}
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="Completion"]/*' />
public Task Completion
{
get { return _defaultTarget != null ? _defaultTarget.Completion : _spscTarget!.Completion; }
}
/// <summary>Posts an item to the <see cref="System.Threading.Tasks.Dataflow.ITargetBlock{T}"/>.</summary>
/// <param name="item">The item being offered to the target.</param>
/// <returns>true if the item was accepted by the target block; otherwise, false.</returns>
/// <remarks>
/// This method will return once the target block has decided to accept or decline the item,
/// but unless otherwise dictated by special semantics of the target block, it does not wait
/// for the item to actually be processed (for example, <see cref="System.Threading.Tasks.Dataflow.ActionBlock{T}"/>
/// will return from Post as soon as it has stored the posted item into its input queue). From the perspective
/// of the block's processing, Post is asynchronous. For target blocks that support postponing offered messages,
/// or for blocks that may do more processing in their Post implementation, consider using
/// <see cref="System.Threading.Tasks.Dataflow.DataflowBlock.SendAsync{TInput}(ITargetBlock{TInput}, TInput)">SendAsync</see>,
/// which will return immediately and will enable the target to postpone the posted message and later consume it
/// after SendAsync returns.
/// </remarks>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public bool Post(TInput item)
{
// Even though this method is available with the exact same functionality as an extension method
// on ITargetBlock, using that extension method goes through an interface call on ITargetBlock,
// which for very high-throughput scenarios shows up as noticeable overhead on certain architectures.
// We can eliminate that call for direct ActionBlock usage by providing the same method as an instance method.
return _defaultTarget != null ?
_defaultTarget.OfferMessage(Common.SingleMessageHeader, item, null, false) == DataflowMessageStatus.Accepted :
_spscTarget!.Post(item);
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Targets/Member[@name="OfferMessage"]/*' />
DataflowMessageStatus ITargetBlock<TInput>.OfferMessage(DataflowMessageHeader messageHeader, TInput messageValue, ISourceBlock<TInput>? source, bool consumeToAccept)
{
return _defaultTarget != null ?
_defaultTarget.OfferMessage(messageHeader, messageValue, source, consumeToAccept) :
_spscTarget!.OfferMessage(messageHeader, messageValue, source, consumeToAccept);
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Targets/Member[@name="InputCount"]/*' />
public int InputCount
{
get { return _defaultTarget != null ? _defaultTarget.InputCount : _spscTarget!.InputCount; }
}
/// <summary>Gets the number of messages waiting to be processed. This must only be used from the debugger.</summary>
private int InputCountForDebugger
{
get { return _defaultTarget != null ? _defaultTarget.GetDebuggingInformation().InputCount : _spscTarget!.InputCount; }
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="ToString"]/*' />
public override string ToString()
{
return Common.GetNameForDebugger(this, _defaultTarget != null ? _defaultTarget.DataflowBlockOptions : _spscTarget!.DataflowBlockOptions);
}
/// <summary>The data to display in the debugger display attribute.</summary>
private object DebuggerDisplayContent =>
$"{(Common.GetNameForDebugger(this, _defaultTarget != null ? _defaultTarget.DataflowBlockOptions : _spscTarget!.DataflowBlockOptions))}, InputCount = {InputCountForDebugger}";
/// <summary>Gets the data to display in the debugger display attribute for this instance.</summary>
object IDebuggerDisplay.Content { get { return DebuggerDisplayContent; } }
/// <summary>Provides a debugger type proxy for the Call.</summary>
private sealed class DebugView
{
/// <summary>The action block being viewed.</summary>
private readonly ActionBlock<TInput> _actionBlock;
/// <summary>The action block's default target being viewed.</summary>
private readonly TargetCore<TInput>.DebuggingInformation? _defaultDebugInfo;
/// <summary>The action block's SPSC target being viewed.</summary>
private readonly SpscTargetCore<TInput>.DebuggingInformation? _spscDebugInfo;
/// <summary>Initializes the debug view.</summary>
/// <param name="actionBlock">The target being debugged.</param>
public DebugView(ActionBlock<TInput> actionBlock)
{
Debug.Assert(actionBlock != null, "Need a block with which to construct the debug view.");
_actionBlock = actionBlock;
if (_actionBlock._defaultTarget != null)
{
_defaultDebugInfo = actionBlock._defaultTarget!.GetDebuggingInformation();
}
else
{
_spscDebugInfo = actionBlock._spscTarget!.GetDebuggingInformation();
}
}
/// <summary>Gets the messages waiting to be processed.</summary>
public IEnumerable<TInput> InputQueue
{
get { return _defaultDebugInfo != null ? _defaultDebugInfo.InputQueue : _spscDebugInfo!.InputQueue; }
}
/// <summary>Gets any postponed messages.</summary>
public QueuedMap<ISourceBlock<TInput>, DataflowMessageHeader>? PostponedMessages
{
get { return _defaultDebugInfo?.PostponedMessages; }
}
/// <summary>Gets the number of outstanding input operations.</summary>
public int CurrentDegreeOfParallelism
{
get { return _defaultDebugInfo != null ? _defaultDebugInfo.CurrentDegreeOfParallelism : _spscDebugInfo!.CurrentDegreeOfParallelism; }
}
/// <summary>Gets the ExecutionDataflowBlockOptions used to configure this block.</summary>
public ExecutionDataflowBlockOptions DataflowBlockOptions
{
get { return _defaultDebugInfo != null ? _defaultDebugInfo.DataflowBlockOptions : _spscDebugInfo!.DataflowBlockOptions; }
}
/// <summary>Gets whether the block is declining further messages.</summary>
public bool IsDecliningPermanently
{
get { return _defaultDebugInfo != null ? _defaultDebugInfo.IsDecliningPermanently : _spscDebugInfo!.IsDecliningPermanently; }
}
/// <summary>Gets whether the block is completed.</summary>
public bool IsCompleted
{
get { return _defaultDebugInfo != null ? _defaultDebugInfo.IsCompleted : _spscDebugInfo!.IsCompleted; }
}
/// <summary>Gets the block's Id.</summary>
public int Id { get { return Common.GetBlockId(_actionBlock); } }
}
}
}
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