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Block copy in List AddRange(ReadOnlySpan) and CopyTo(Span) #685

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Merged
SimonCropp merged 1 commit into from
Oct 12, 2026
Merged

Block copy in List AddRange(ReadOnlySpan) and CopyTo(Span) #685

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89 changes: 87 additions & 2 deletions src/Polyfill/Polyfill_List.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,12 +20,75 @@ public static ReadOnlyCollection<T> AsReadOnly<T>(this IList<T> target) =>
//Link: https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.addrange?view=net-11.0
public static void AddRange<T>(this List<T> target, ReadOnlySpan<T> source)
{
if (source.IsEmpty)
{
return;
}

var length = source.Length;

// List<T>.AddRange block copies an ICollection<T>. On .NET Framework it goes through an extra
// temporary array, which only pays off when the items can be block copied without GC bookkeeping.
if (length >= blockCopyThreshold
#if !NETCOREAPP
&& typeof(T).IsPrimitive
#endif
)
{
var pool = System.Buffers.ArrayPool<T>.Shared;
var buffer = pool.Rent(length);
try
{
source.CopyTo(buffer);
target.AddRange(new ArraySegment<T>(buffer, 0, length));
}
finally
{
ReturnToPool(pool, buffer, length);
}

return;
}

// Grow once, using the same doubling as List<T>, instead of several times while adding
var required = target.Count + length;
var capacity = target.Capacity;
if (required > capacity)
{
var newCapacity = capacity * 2;
if ((uint) newCapacity > 0x7FEFFFFF)
{
newCapacity = 0x7FEFFFFF;
}

if (newCapacity < required)
{
newCapacity = required;
}

target.Capacity = newCapacity;
}

foreach (var item in source)
{
target.Add(item);
}
}

// Below this the cost of renting a buffer outweighs the block copy
const int blockCopyThreshold = 64;

static void ReturnToPool<T>(System.Buffers.ArrayPool<T> pool, T[] buffer, int length)
{
// Do not keep references alive in the pool
if (!typeof(T).IsPrimitive)
{
Array.Clear(buffer, 0, length);
}

pool.Return(buffer);
}

/// <summary>Inserts the elements of a span into the <see cref="List{T}"/> at the specified index.</summary>
//Link: https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.insertrange?view=net-11.0
public static void InsertRange<T>(this List<T> target, int index, ReadOnlySpan<T> source)
Expand All @@ -51,10 +114,32 @@ public static void CopyTo<T>(this List<T> target, Span<T> destination)
throw new ArgumentException("Destination is too short.", nameof(destination));
}

for (var index = 0; index < target.Count; index++)
#if NET5_0_OR_GREATER
System.Runtime.InteropServices.CollectionsMarshal.AsSpan(target).CopyTo(destination);
#else
var count = target.Count;
if (count < blockCopyThreshold)
{
destination[index] = target[index];
for (var index = 0; index < count; index++)
{
destination[index] = target[index];
}

return;
}

var pool = System.Buffers.ArrayPool<T>.Shared;
var buffer = pool.Rent(count);
try
{
target.CopyTo(0, buffer, 0, count);
new ReadOnlySpan<T>(buffer, 0, count).CopyTo(destination);
}
finally
{
ReturnToPool(pool, buffer, count);
}
#endif
}
#endif

Expand Down
66 changes: 64 additions & 2 deletions src/Split/net461/Polyfill_List.cs
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -13,11 +13,57 @@ public static ReadOnlyCollection<T> AsReadOnly<T>(this IList<T> target) =>
/// <summary>Adds the elements of the specified span to the end of the <see cref="List{T}"/>.</summary>
public static void AddRange<T>(this List<T> target, ReadOnlySpan<T> source)
{
if (source.IsEmpty)
{
return;
}
var length = source.Length;
if (length >= blockCopyThreshold
&& typeof(T).IsPrimitive
)
{
var pool = System.Buffers.ArrayPool<T>.Shared;
var buffer = pool.Rent(length);
try
{
source.CopyTo(buffer);
target.AddRange(new ArraySegment<T>(buffer, 0, length));
}
finally
{
ReturnToPool(pool, buffer, length);
}
return;
}
var required = target.Count + length;
var capacity = target.Capacity;
if (required > capacity)
{
var newCapacity = capacity * 2;
if ((uint) newCapacity > 0x7FEFFFFF)
{
newCapacity = 0x7FEFFFFF;
}
if (newCapacity < required)
{
newCapacity = required;
}
target.Capacity = newCapacity;
}
foreach (var item in source)
{
target.Add(item);
}
}
const int blockCopyThreshold = 64;
static void ReturnToPool<T>(System.Buffers.ArrayPool<T> pool, T[] buffer, int length)
{
if (!typeof(T).IsPrimitive)
{
Array.Clear(buffer, 0, length);
}
pool.Return(buffer);
}
/// <summary>Inserts the elements of a span into the <see cref="List{T}"/> at the specified index.</summary>
public static void InsertRange<T>(this List<T> target, int index, ReadOnlySpan<T> source)
{
Expand All @@ -38,9 +84,25 @@ public static void CopyTo<T>(this List<T> target, Span<T> destination)
{
throw new ArgumentException("Destination is too short.", nameof(destination));
}
for (var index = 0; index < target.Count; index++)
var count = target.Count;
if (count < blockCopyThreshold)
{
for (var index = 0; index < count; index++)
{
destination[index] = target[index];
}
return;
}
var pool = System.Buffers.ArrayPool<T>.Shared;
var buffer = pool.Rent(count);
try
{
target.CopyTo(0, buffer, 0, count);
new ReadOnlySpan<T>(buffer, 0, count).CopyTo(destination);
}
finally
{
destination[index] = target[index];
ReturnToPool(pool, buffer, count);
}
}
#endif
Expand Down
66 changes: 64 additions & 2 deletions src/Split/net462/Polyfill_List.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -13,11 +13,57 @@ public static ReadOnlyCollection<T> AsReadOnly<T>(this IList<T> target) =>
/// <summary>Adds the elements of the specified span to the end of the <see cref="List{T}"/>.</summary>
public static void AddRange<T>(this List<T> target, ReadOnlySpan<T> source)
{
if (source.IsEmpty)
{
return;
}
var length = source.Length;
if (length >= blockCopyThreshold
&& typeof(T).IsPrimitive
)
{
var pool = System.Buffers.ArrayPool<T>.Shared;
var buffer = pool.Rent(length);
try
{
source.CopyTo(buffer);
target.AddRange(new ArraySegment<T>(buffer, 0, length));
}
finally
{
ReturnToPool(pool, buffer, length);
}
return;
}
var required = target.Count + length;
var capacity = target.Capacity;
if (required > capacity)
{
var newCapacity = capacity * 2;
if ((uint) newCapacity > 0x7FEFFFFF)
{
newCapacity = 0x7FEFFFFF;
}
if (newCapacity < required)
{
newCapacity = required;
}
target.Capacity = newCapacity;
}
foreach (var item in source)
{
target.Add(item);
}
}
const int blockCopyThreshold = 64;
static void ReturnToPool<T>(System.Buffers.ArrayPool<T> pool, T[] buffer, int length)
{
if (!typeof(T).IsPrimitive)
{
Array.Clear(buffer, 0, length);
}
pool.Return(buffer);
}
/// <summary>Inserts the elements of a span into the <see cref="List{T}"/> at the specified index.</summary>
public static void InsertRange<T>(this List<T> target, int index, ReadOnlySpan<T> source)
{
Expand All @@ -38,9 +84,25 @@ public static void CopyTo<T>(this List<T> target, Span<T> destination)
{
throw new ArgumentException("Destination is too short.", nameof(destination));
}
for (var index = 0; index < target.Count; index++)
var count = target.Count;
if (count < blockCopyThreshold)
{
for (var index = 0; index < count; index++)
{
destination[index] = target[index];
}
return;
}
var pool = System.Buffers.ArrayPool<T>.Shared;
var buffer = pool.Rent(count);
try
{
target.CopyTo(0, buffer, 0, count);
new ReadOnlySpan<T>(buffer, 0, count).CopyTo(destination);
}
finally
{
destination[index] = target[index];
ReturnToPool(pool, buffer, count);
}
}
#endif
Expand Down
66 changes: 64 additions & 2 deletions src/Split/net47/Polyfill_List.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -13,11 +13,57 @@ public static ReadOnlyCollection<T> AsReadOnly<T>(this IList<T> target) =>
/// <summary>Adds the elements of the specified span to the end of the <see cref="List{T}"/>.</summary>
public static void AddRange<T>(this List<T> target, ReadOnlySpan<T> source)
{
if (source.IsEmpty)
{
return;
}
var length = source.Length;
if (length >= blockCopyThreshold
&& typeof(T).IsPrimitive
)
{
var pool = System.Buffers.ArrayPool<T>.Shared;
var buffer = pool.Rent(length);
try
{
source.CopyTo(buffer);
target.AddRange(new ArraySegment<T>(buffer, 0, length));
}
finally
{
ReturnToPool(pool, buffer, length);
}
return;
}
var required = target.Count + length;
var capacity = target.Capacity;
if (required > capacity)
{
var newCapacity = capacity * 2;
if ((uint) newCapacity > 0x7FEFFFFF)
{
newCapacity = 0x7FEFFFFF;
}
if (newCapacity < required)
{
newCapacity = required;
}
target.Capacity = newCapacity;
}
foreach (var item in source)
{
target.Add(item);
}
}
const int blockCopyThreshold = 64;
static void ReturnToPool<T>(System.Buffers.ArrayPool<T> pool, T[] buffer, int length)
{
if (!typeof(T).IsPrimitive)
{
Array.Clear(buffer, 0, length);
}
pool.Return(buffer);
}
/// <summary>Inserts the elements of a span into the <see cref="List{T}"/> at the specified index.</summary>
public static void InsertRange<T>(this List<T> target, int index, ReadOnlySpan<T> source)
{
Expand All @@ -38,9 +84,25 @@ public static void CopyTo<T>(this List<T> target, Span<T> destination)
{
throw new ArgumentException("Destination is too short.", nameof(destination));
}
for (var index = 0; index < target.Count; index++)
var count = target.Count;
if (count < blockCopyThreshold)
{
for (var index = 0; index < count; index++)
{
destination[index] = target[index];
}
return;
}
var pool = System.Buffers.ArrayPool<T>.Shared;
var buffer = pool.Rent(count);
try
{
target.CopyTo(0, buffer, 0, count);
new ReadOnlySpan<T>(buffer, 0, count).CopyTo(destination);
}
finally
{
destination[index] = target[index];
ReturnToPool(pool, buffer, count);
}
}
#endif
Expand Down
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