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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.
// See the LICENSE file in the project root for more information.
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
//
// Scheduling.cs
//
// Infrastructure for setting up concurrent work, marshaling exceptions, determining
// the recommended degree-of-parallelism, and so forth.
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Runtime.InteropServices;
using System.Threading;
using System.Diagnostics;
using System.Threading.Tasks;
using System.Security;
namespace System.Linq.Parallel
{
//-----------------------------------------------------------------------------------
// A simple helper class that offers common task scheduling functionality.
//
internal static class Scheduling
{
// Whether to preserve order by default, when neither AsOrdered nor AsUnordered is used.
internal const bool DefaultPreserveOrder = false;
// The default degree of parallelism, or -1 if unspecified. Dev unit tests set this value
// to change the default DOP.
internal static int DefaultDegreeOfParallelism = Math.Min(Environment.ProcessorCount, MAX_SUPPORTED_DOP);
// The size to use for bounded buffers.
internal const int DEFAULT_BOUNDED_BUFFER_CAPACITY = 512;
// The number of bytes we want "chunks" to be, when partitioning, etc. We choose 4 cache
// lines worth, assuming 128b cache line. Most (popular) architectures use 64b cache lines,
// but choosing 128b works for 64b too whereas a multiple of 64b isn't necessarily sufficient
// for 128b cache systems. So 128b it is.
internal const int DEFAULT_BYTES_PER_CHUNK = 128 * 4;
// The number of milliseconds before we assume a producer has been zombied.
internal const int ZOMBIED_PRODUCER_TIMEOUT = Timeout.Infinite;
#if MONO
/* limit to degree of 16 to avoid too much contention */
internal const int MAX_SUPPORTED_DOP = 16;
#else
// The largest number of partitions that PLINQ supports.
internal const int MAX_SUPPORTED_DOP = 512;
#endif
//-----------------------------------------------------------------------------------
// Calculates the proper amount of DOP. This takes into consideration dynamic nesting.
//
internal static int GetDefaultDegreeOfParallelism()
{
return DefaultDegreeOfParallelism;
}
//-----------------------------------------------------------------------------------
// Gets the recommended "chunk size" for a particular CLR type.
//
// Notes:
// We try to recommend some reasonable "chunk size" for the data, but this is
// clearly a tradeoff, and requires a bit of experimentation. A larger chunk size
// can help locality, but if it's too big we may end up either stalling another
// partition (if enumerators are calculating data on demand) or skewing the
// distribution of data among the partitions.
//
internal static int GetDefaultChunkSize<T>()
{
int chunkSize;
// Because of the lack of typeof(T).IsValueType we need two pieces of information
// to determine this. default(T) will return a non null for Value Types, except those
// using Nullable<>, that is why we need a second condition.
if (default(T) != null || Nullable.GetUnderlyingType(typeof(T)) != null)
{
// Marshal.SizeOf fails for value types that don't have explicit layouts. We
// just fall back to some arbitrary constant in that case. Is there a better way?
{
// We choose '128' because this ensures, no matter the actual size of the value type,
// the total bytes used will be a multiple of 128. This ensures it's cache aligned.
chunkSize = 128;
}
}
else
{
Debug.Assert((DEFAULT_BYTES_PER_CHUNK % IntPtr.Size) == 0, "bytes per chunk should be a multiple of pointer size");
chunkSize = (DEFAULT_BYTES_PER_CHUNK / IntPtr.Size);
}
TraceHelpers.TraceInfo("Scheduling::GetDefaultChunkSize({0}) -- returning {1}", typeof(T), chunkSize);
return chunkSize;
}
}
}
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