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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.
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
//
// TransformBlock.cs
//
//
// A propagator block that runs a function on each input to produce a single output.
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Threading.Tasks.Dataflow.Internal;
namespace System.Threading.Tasks.Dataflow
{
/// <summary>Provides a dataflow block that invokes a provided <see cref="System.Func{TInput,TOutput}"/> delegate for every data element received.</summary>
/// <typeparam name="TInput">Specifies the type of data received and operated on by this <see cref="TransformBlock{TInput,TOutput}"/>.</typeparam>
/// <typeparam name="TOutput">Specifies the type of data output by this <see cref="TransformBlock{TInput,TOutput}"/>.</typeparam>
[DebuggerDisplay("{DebuggerDisplayContent,nq}")]
[DebuggerTypeProxy(typeof(TransformBlock<,>.DebugView))]
public sealed class TransformBlock<TInput, TOutput> : IPropagatorBlock<TInput, TOutput>, IReceivableSourceBlock<TOutput>, IDebuggerDisplay
{
/// <summary>The target side.</summary>
private readonly TargetCore<TInput> _target;
/// <summary>Buffer used to reorder outputs that may have completed out-of-order between the target half and the source half.</summary>
private readonly ReorderingBuffer<TOutput>? _reorderingBuffer;
/// <summary>The source side.</summary>
private readonly SourceCore<TOutput> _source;
/// <summary>Gets the object to use for writing to the source when multiple threads may be involved.</summary>
/// <remarks>
/// If a reordering buffer is used, it is safe for multiple threads to write to concurrently and handles safe
/// access to the source. If there's no reordering buffer because no parallelism is used, then only one thread at
/// a time will try to access the source, anyway. But, if there's no reordering buffer and parallelism is being
/// employed, then multiple threads may try to access the source concurrently, in which case we need to manually
/// synchronize all such access, and this lock is used for that purpose.
/// </remarks>
private object ParallelSourceLock { get { return _source; } }
/// <summary>Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/>.</summary>
/// <param name="transform">The function to invoke with each data element received.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="transform"/> is null (Nothing in Visual Basic).</exception>
public TransformBlock(Func<TInput, TOutput> transform) :
this(transform, null, ExecutionDataflowBlockOptions.Default)
{ }
/// <summary>
/// Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/> and
/// <see cref="ExecutionDataflowBlockOptions"/>.
/// </summary>
/// <param name="transform">The function to invoke with each data element received.</param>
/// <param name="dataflowBlockOptions">The options with which to configure this <see cref="TransformBlock{TInput,TOutput}"/>.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="transform"/> is null (Nothing in Visual Basic).</exception>
/// <exception cref="System.ArgumentNullException">The <paramref name="dataflowBlockOptions"/> is null (Nothing in Visual Basic).</exception>
public TransformBlock(Func<TInput, TOutput> transform, ExecutionDataflowBlockOptions dataflowBlockOptions) :
this(transform, null, dataflowBlockOptions)
{ }
/// <summary>Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/>.</summary>
/// <param name="transform">The function to invoke with each data element received.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="transform"/> is null (Nothing in Visual Basic).</exception>
public TransformBlock(Func<TInput, Task<TOutput>> transform) :
this(null, transform, ExecutionDataflowBlockOptions.Default)
{ }
/// <summary>
/// Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/>
/// and <see cref="ExecutionDataflowBlockOptions"/>.
/// </summary>
/// <param name="transform">The function to invoke with each data element received.</param>
/// <param name="dataflowBlockOptions">The options with which to configure this <see cref="TransformBlock{TInput,TOutput}"/>.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="transform"/> is null (Nothing in Visual Basic).</exception>
/// <exception cref="System.ArgumentNullException">The <paramref name="dataflowBlockOptions"/> is null (Nothing in Visual Basic).</exception>
public TransformBlock(Func<TInput, Task<TOutput>> transform, ExecutionDataflowBlockOptions dataflowBlockOptions) :
this(null, transform, dataflowBlockOptions)
{ }
/// <summary>
/// Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/>
/// and <see cref="DataflowBlockOptions"/>.
/// </summary>
/// <param name="transformSync">The synchronous function to invoke with each data element received.</param>
/// <param name="transformAsync">The asynchronous function to invoke with each data element received.</param>
/// <param name="dataflowBlockOptions">The options with which to configure this <see cref="TransformBlock{TInput,TOutput}"/>.</param>
/// <exception cref="System.ArgumentNullException">The <paramref name="transformSync"/> and <paramref name="transformAsync"/> are both null (Nothing in Visual Basic).</exception>
/// <exception cref="System.ArgumentNullException">The <paramref name="dataflowBlockOptions"/> is null (Nothing in Visual Basic).</exception>
private TransformBlock(Func<TInput, TOutput>? transformSync, Func<TInput, Task<TOutput>>? transformAsync, ExecutionDataflowBlockOptions dataflowBlockOptions)
{
if (dataflowBlockOptions is null)
{
throw new ArgumentNullException(nameof(dataflowBlockOptions));
}
if (transformSync == null && transformAsync == null) throw new ArgumentNullException("transform");
if (dataflowBlockOptions == null) throw new ArgumentNullException(nameof(dataflowBlockOptions));
Debug.Assert(transformSync == null ^ transformAsync == null, "Exactly one of transformSync and transformAsync must be null.");
// Ensure we have options that can't be changed by the caller
dataflowBlockOptions = dataflowBlockOptions.DefaultOrClone();
// Initialize onItemsRemoved delegate if necessary
Action<ISourceBlock<TOutput>, int>? onItemsRemoved = null;
if (dataflowBlockOptions.BoundedCapacity > 0)
onItemsRemoved = static (owningSource, count) => ((TransformBlock<TInput, TOutput>)owningSource)._target.ChangeBoundingCount(-count);
// Initialize source component.
_source = new SourceCore<TOutput>(this, dataflowBlockOptions,
static owningSource => ((TransformBlock<TInput, TOutput>)owningSource)._target.Complete(exception: null, dropPendingMessages: true),
onItemsRemoved);
// If parallelism is employed, we will need to support reordering messages that complete out-of-order.
// However, a developer can override this with EnsureOrdered == false.
if (dataflowBlockOptions.SupportsParallelExecution && dataflowBlockOptions.EnsureOrdered)
{
_reorderingBuffer = new ReorderingBuffer<TOutput>(this, static (owningSource, message) => ((TransformBlock<TInput, TOutput>)owningSource)._source.AddMessage(message));
}
// Create the underlying target
if (transformSync != null) // sync
{
_target = new TargetCore<TInput>(this,
messageWithId => ProcessMessage(transformSync, messageWithId),
_reorderingBuffer, dataflowBlockOptions, TargetCoreOptions.None);
}
else // async
{
Debug.Assert(transformAsync != null, "Incorrect delegate type.");
_target = new TargetCore<TInput>(this,
messageWithId => ProcessMessageWithTask(transformAsync, messageWithId),
_reorderingBuffer, dataflowBlockOptions, TargetCoreOptions.UsesAsyncCompletion);
}
// Link up the target half with the source half. In doing so,
// ensure exceptions are propagated, and let the source know no more messages will arrive.
// As the target has completed, and as the target synchronously pushes work
// through the reordering buffer when async processing completes,
// we know for certain that no more messages will need to be sent to the source.
_target.Completion.ContinueWith(static (completed, state) =>
{
var sourceCore = (SourceCore<TOutput>)state!;
if (completed.IsFaulted) sourceCore.AddAndUnwrapAggregateException(completed.Exception!);
sourceCore.Complete();
}, _source, CancellationToken.None, Common.GetContinuationOptions(), TaskScheduler.Default);
// It is possible that the source half may fault on its own, e.g. due to a task scheduler exception.
// In those cases we need to fault the target half to drop its buffered messages and to release its
// reservations. This should not create an infinite loop, because all our implementations are designed
// to handle multiple completion requests and to carry over only one.
_source.Completion.ContinueWith(static (completed, state) =>
{
var thisBlock = ((TransformBlock<TInput, TOutput>)state!) as IDataflowBlock;
Debug.Assert(completed.IsFaulted, "The source must be faulted in order to trigger a target completion.");
thisBlock.Fault(completed.Exception!);
}, this, CancellationToken.None, Common.GetContinuationOptions() | TaskContinuationOptions.OnlyOnFaulted, TaskScheduler.Default);
// Handle async cancellation requests by declining on the target
Common.WireCancellationToComplete(
dataflowBlockOptions.CancellationToken, Completion, static (state, _) => ((TargetCore<TInput>)state!).Complete(exception: null, dropPendingMessages: true), _target);
DataflowEtwProvider etwLog = DataflowEtwProvider.Log;
if (etwLog.IsEnabled())
{
etwLog.DataflowBlockCreated(this, dataflowBlockOptions);
}
}
/// <summary>Processes the message with a user-provided transform function that returns a TOutput.</summary>
/// <param name="transform">The transform function to use to process the message.</param>
/// <param name="messageWithId">The message to be processed.</param>
private void ProcessMessage(Func<TInput, TOutput> transform, KeyValuePair<TInput, long> messageWithId)
{
// Process the input message to get the output message
TOutput? outputItem = default(TOutput);
bool itemIsValid = false;
try
{
outputItem = transform(messageWithId.Key);
itemIsValid = true;
}
catch (Exception exc)
{
// If this exception represents cancellation, swallow it rather than shutting down the block.
if (!Common.IsCooperativeCancellation(exc)) throw;
}
finally
{
// If we were not successful in producing an item, update the bounding
// count to reflect that we're done with this input item.
if (!itemIsValid) _target.ChangeBoundingCount(-1);
// If there's no reordering buffer (because we're running sequentially or ordering was disabled),
// simply pass the output message through. Otherwise, there's a reordering buffer,
// so add to it instead (if a reordering buffer is used, we always need
// to output the message to it, even if the operation failed and outputMessage
// is null... this is because the reordering buffer cares about a strict sequence
// of IDs, and it needs to know when a particular ID has completed. It will eliminate
// null messages accordingly.)
if (_reorderingBuffer == null)
{
if (itemIsValid)
{
if (_target.DataflowBlockOptions.MaxDegreeOfParallelism == 1)
{
_source.AddMessage(outputItem!);
}
else
{
lock (ParallelSourceLock)
{
_source.AddMessage(outputItem!);
}
}
}
}
else _reorderingBuffer.AddItem(messageWithId.Value, outputItem!, itemIsValid);
}
}
/// <summary>Processes the message with a user-provided transform function that returns a task of TOutput.</summary>
/// <param name="transform">The transform function to use to process the message.</param>
/// <param name="messageWithId">The message to be processed.</param>
private void ProcessMessageWithTask(Func<TInput, Task<TOutput>> transform, KeyValuePair<TInput, long> messageWithId)
{
Debug.Assert(transform != null, "Function to invoke is required.");
// Run the transform function to get the task that represents the operation's completion
Task<TOutput>? task = null;
Exception? caughtException = null;
try
{
task = transform(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);
_target.Complete(caughtException, dropPendingMessages: true, storeExceptionEvenIfAlreadyCompleting: true, unwrapInnerExceptions: false);
}
// If there's a reordering buffer, notify it that this message is done.
_reorderingBuffer?.IgnoreItem(messageWithId.Value);
// Signal that we're done this async operation, and remove the bounding
// count for the input item that didn't yield any output.
_target.SignalOneAsyncMessageCompleted(boundingCountChange: -1);
return;
}
// Otherwise, join with the asynchronous operation when it completes.
task.ContinueWith(static (completed, state) =>
{
var tuple = (Tuple<TransformBlock<TInput, TOutput>, KeyValuePair<TInput, long>>)state!;
tuple.Item1.AsyncCompleteProcessMessageWithTask(completed, tuple.Item2);
}, Tuple.Create(this, messageWithId), CancellationToken.None,
Common.GetContinuationOptions(TaskContinuationOptions.ExecuteSynchronously), TaskScheduler.Default);
}
/// <summary>Completes the processing of an asynchronous message.</summary>
/// <param name="completed">The completed task storing the output data generated for an input message.</param>
/// <param name="messageWithId">The originating message</param>
private void AsyncCompleteProcessMessageWithTask(Task<TOutput> completed, KeyValuePair<TInput, long> messageWithId)
{
Debug.Assert(completed != null, "Completed task is required.");
Debug.Assert(completed.IsCompleted, "Task must be completed to be here.");
bool isBounded = _target.IsBounded;
bool gotOutputItem = false;
TOutput? outputItem = default(TOutput);
switch (completed.Status)
{
case TaskStatus.RanToCompletion:
outputItem = completed.Result;
gotOutputItem = true;
break;
case TaskStatus.Faulted:
// 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.
AggregateException aggregate = completed.Exception!;
Common.StoreDataflowMessageValueIntoExceptionData(aggregate, messageWithId.Key, targetInnerExceptions: true);
_target.Complete(aggregate, dropPendingMessages: true, storeExceptionEvenIfAlreadyCompleting: true, unwrapInnerExceptions: true);
break;
// Nothing special to do for cancellation
}
// Adjust the bounding count if necessary (we only need to decrement it for faulting
// and cancellation, since in the case of success we still have an item that's now in the output buffer).
// Even though this is more costly (again, only in the non-success case, we do this before we store the
// message, so that if there's a race to remove the element from the source buffer, the count is
// appropriately incremented before it's decremented.
if (!gotOutputItem && isBounded) _target.ChangeBoundingCount(-1);
// If there's no reordering buffer (because we're running sequentially or ordering is disabled),
// and we got a message, simply pass the output message through.
if (_reorderingBuffer == null)
{
if (gotOutputItem)
{
if (_target.DataflowBlockOptions.MaxDegreeOfParallelism == 1)
{
_source.AddMessage(outputItem!);
}
else
{
lock (ParallelSourceLock)
{
_source.AddMessage(outputItem!);
}
}
}
}
// Otherwise, there's a reordering buffer, so add to it instead.
// Even if something goes wrong, we need to update the
// reordering buffer, so it knows that an item isn't missing.
else _reorderingBuffer.AddItem(messageWithId.Value, outputItem!, itemIsValid: gotOutputItem);
// Let the target know that one of the asynchronous operations it launched has completed.
_target.SignalOneAsyncMessageCompleted();
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="Complete"]/*' />
public void Complete() { _target.Complete(exception: null, dropPendingMessages: false); }
/// <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));
}
_target.Complete(exception, dropPendingMessages: true);
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="LinkTo"]/*' />
public IDisposable LinkTo(ITargetBlock<TOutput> target, DataflowLinkOptions linkOptions)
{
return _source.LinkTo(target, linkOptions);
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="TryReceive"]/*' />
public bool TryReceive(Predicate<TOutput>? filter, [MaybeNullWhen(false)] out TOutput item)
{
return _source.TryReceive(filter, out item);
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="TryReceiveAll"]/*' />
public bool TryReceiveAll([NotNullWhen(true)] out IList<TOutput>? items) { return _source.TryReceiveAll(out items); }
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="Completion"]/*' />
public Task Completion { get { return _source.Completion; } }
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Targets/Member[@name="InputCount"]/*' />
public int InputCount { get { return _target.InputCount; } }
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="OutputCount"]/*' />
public int OutputCount { get { return _source.OutputCount; } }
/// <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 _target.OfferMessage(messageHeader, messageValue, source, consumeToAccept);
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
TOutput? ISourceBlock<TOutput>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out bool messageConsumed)
{
return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ReserveMessage"]/*' />
bool ISourceBlock<TOutput>.ReserveMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target)
{
return _source.ReserveMessage(messageHeader, target);
}
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ReleaseReservation"]/*' />
void ISourceBlock<TOutput>.ReleaseReservation(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target)
{
_source.ReleaseReservation(messageHeader, target);
}
/// <summary>Gets the number of messages waiting to be processed. This must only be used from the debugger as it avoids taking necessary locks.</summary>
private int InputCountForDebugger { get { return _target.GetDebuggingInformation().InputCount; } }
/// <summary>Gets the number of messages waiting to be processed. This must only be used from the debugger as it avoids taking necessary locks.</summary>
private int OutputCountForDebugger { get { return _source.GetDebuggingInformation().OutputCount; } }
/// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="ToString"]/*' />
public override string ToString() { return Common.GetNameForDebugger(this, _source.DataflowBlockOptions); }
/// <summary>The data to display in the debugger display attribute.</summary>
private object DebuggerDisplayContent =>
$"{Common.GetNameForDebugger(this, _source.DataflowBlockOptions)}, InputCount = {InputCountForDebugger}, OutputCount = {OutputCountForDebugger}";
/// <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 TransformBlock.</summary>
private sealed class DebugView
{
/// <summary>The transform being viewed.</summary>
private readonly TransformBlock<TInput, TOutput> _transformBlock;
/// <summary>The target half of the block being viewed.</summary>
private readonly TargetCore<TInput>.DebuggingInformation _targetDebuggingInformation;
/// <summary>The source half of the block being viewed.</summary>
private readonly SourceCore<TOutput>.DebuggingInformation _sourceDebuggingInformation;
/// <summary>Initializes the debug view.</summary>
/// <param name="transformBlock">The transform being viewed.</param>
public DebugView(TransformBlock<TInput, TOutput> transformBlock)
{
Debug.Assert(transformBlock != null, "Need a block with which to construct the debug view.");
_transformBlock = transformBlock;
_targetDebuggingInformation = transformBlock._target.GetDebuggingInformation();
_sourceDebuggingInformation = transformBlock._source.GetDebuggingInformation();
}
/// <summary>Gets the messages waiting to be processed.</summary>
public IEnumerable<TInput> InputQueue { get { return _targetDebuggingInformation.InputQueue; } }
/// <summary>Gets any postponed messages.</summary>
public QueuedMap<ISourceBlock<TInput>, DataflowMessageHeader>? PostponedMessages { get { return _targetDebuggingInformation.PostponedMessages; } }
/// <summary>Gets the messages waiting to be received.</summary>
public IEnumerable<TOutput> OutputQueue { get { return _sourceDebuggingInformation.OutputQueue; } }
/// <summary>Gets the number of outstanding input operations.</summary>
public int CurrentDegreeOfParallelism { get { return _targetDebuggingInformation.CurrentDegreeOfParallelism; } }
/// <summary>Gets the task being used for output processing.</summary>
public Task? TaskForOutputProcessing { get { return _sourceDebuggingInformation.TaskForOutputProcessing; } }
/// <summary>Gets the DataflowBlockOptions used to configure this block.</summary>
public ExecutionDataflowBlockOptions DataflowBlockOptions { get { return _targetDebuggingInformation.DataflowBlockOptions; } }
/// <summary>Gets whether the block is declining further messages.</summary>
public bool IsDecliningPermanently { get { return _targetDebuggingInformation.IsDecliningPermanently; } }
/// <summary>Gets whether the block is completed.</summary>
public bool IsCompleted { get { return _sourceDebuggingInformation.IsCompleted; } }
/// <summary>Gets the block's Id.</summary>
public int Id { get { return Common.GetBlockId(_transformBlock); } }
/// <summary>Gets the set of all targets linked from this block.</summary>
public TargetRegistry<TOutput> LinkedTargets { get { return _sourceDebuggingInformation.LinkedTargets; } }
/// <summary>Gets the target that holds a reservation on the next message, if any.</summary>
public ITargetBlock<TOutput>? NextMessageReservedFor { get { return _sourceDebuggingInformation.NextMessageReservedFor; } }
}
}
}
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