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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.
#nullable enable
using System.Buffers;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;
using EditorBrowsableAttribute = System.ComponentModel.EditorBrowsableAttribute;
using EditorBrowsableState = System.ComponentModel.EditorBrowsableState;
using Internal.Runtime.CompilerServices;
#if BIT64
using nint = System.Int64;
using nuint = System.UInt64;
#else // BIT64
using nint = System.Int32;
using nuint = System.UInt32;
#endif // BIT64
namespace System
{
/// <summary>
/// Memory represents a contiguous region of arbitrary memory similar to <see cref="Span{T}"/>.
/// Unlike <see cref="Span{T}"/>, it is not a byref-like type.
/// </summary>
[DebuggerTypeProxy(typeof(MemoryDebugView<>))]
[DebuggerDisplay("{ToString(),raw}")]
public readonly struct Memory<T> : IEquatable<Memory<T>>
{
// NOTE: With the current implementation, Memory<T> and ReadOnlyMemory<T> must have the same layout,
// as code uses Unsafe.As to cast between them.
// The highest order bit of _index is used to discern whether _object is a pre-pinned array.
// (_index < 0) => _object is a pre-pinned array, so Pin() will not allocate a new GCHandle
// (else) => Pin() needs to allocate a new GCHandle to pin the object.
private readonly object? _object;
private readonly int _index;
private readonly int _length;
/// <summary>
/// Creates a new memory over the entirety of the target array.
/// </summary>
/// <param name="array">The target array.</param>
/// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
/// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Memory(T[]? array)
{
if (array == null)
{
this = default;
return; // returns default
}
if (default(T)! == null && array.GetType() != typeof(T[])) // TODO-NULLABLE: https://github.com/dotnet/roslyn/issues/34757
ThrowHelper.ThrowArrayTypeMismatchException();
_object = array;
_index = 0;
_length = array.Length;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal Memory(T[]? array, int start)
{
if (array == null)
{
if (start != 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
this = default;
return; // returns default
}
if (default(T)! == null && array.GetType() != typeof(T[])) // TODO-NULLABLE: https://github.com/dotnet/roslyn/issues/34757
ThrowHelper.ThrowArrayTypeMismatchException();
if ((uint)start > (uint)array.Length)
ThrowHelper.ThrowArgumentOutOfRangeException();
_object = array;
_index = start;
_length = array.Length - start;
}
/// <summary>
/// Creates a new memory over the portion of the target array beginning
/// at 'start' index and ending at 'end' index (exclusive).
/// </summary>
/// <param name="array">The target array.</param>
/// <param name="start">The index at which to begin the memory.</param>
/// <param name="length">The number of items in the memory.</param>
/// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
/// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in the range (&lt;0 or &gt;=Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Memory(T[]? array, int start, int length)
{
if (array == null)
{
if (start != 0 || length != 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
this = default;
return; // returns default
}
if (default(T)! == null && array.GetType() != typeof(T[])) // TODO-NULLABLE: https://github.com/dotnet/roslyn/issues/34757
ThrowHelper.ThrowArrayTypeMismatchException();
#if BIT64
// See comment in Span<T>.Slice for how this works.
if ((ulong)(uint)start + (ulong)(uint)length > (ulong)(uint)array.Length)
ThrowHelper.ThrowArgumentOutOfRangeException();
#else
if ((uint)start > (uint)array.Length || (uint)length > (uint)(array.Length - start))
ThrowHelper.ThrowArgumentOutOfRangeException();
#endif
_object = array;
_index = start;
_length = length;
}
/// <summary>
/// Creates a new memory from a memory manager that provides specific method implementations beginning
/// at 0 index and ending at 'end' index (exclusive).
/// </summary>
/// <param name="manager">The memory manager.</param>
/// <param name="length">The number of items in the memory.</param>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="length"/> is negative.
/// </exception>
/// <remarks>For internal infrastructure only</remarks>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal Memory(MemoryManager<T> manager, int length)
{
Debug.Assert(manager != null);
if (length < 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
_object = manager;
_index = 0;
_length = length;
}
/// <summary>
/// Creates a new memory from a memory manager that provides specific method implementations beginning
/// at 'start' index and ending at 'end' index (exclusive).
/// </summary>
/// <param name="manager">The memory manager.</param>
/// <param name="start">The index at which to begin the memory.</param>
/// <param name="length">The number of items in the memory.</param>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or <paramref name="length"/> is negative.
/// </exception>
/// <remarks>For internal infrastructure only</remarks>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal Memory(MemoryManager<T> manager, int start, int length)
{
Debug.Assert(manager != null);
if (length < 0 || start < 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
_object = manager;
_index = start;
_length = length;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal Memory(object? obj, int start, int length)
{
// No validation performed in release builds; caller must provide any necessary validation.
// 'obj is T[]' below also handles things like int[] <-> uint[] being convertible
Debug.Assert((obj == null)
|| (typeof(T) == typeof(char) && obj is string)
#if FEATURE_UTF8STRING
|| ((typeof(T) == typeof(byte) || typeof(T) == typeof(Char8)) && obj is Utf8String)
#endif // FEATURE_UTF8STRING
|| (obj is T[])
|| (obj is MemoryManager<T>));
_object = obj;
_index = start;
_length = length;
}
/// <summary>
/// Defines an implicit conversion of an array to a <see cref="Memory{T}"/>
/// </summary>
public static implicit operator Memory<T>(T[]? array) => new Memory<T>(array);
/// <summary>
/// Defines an implicit conversion of a <see cref="ArraySegment{T}"/> to a <see cref="Memory{T}"/>
/// </summary>
public static implicit operator Memory<T>(ArraySegment<T> segment) => new Memory<T>(segment.Array, segment.Offset, segment.Count);
/// <summary>
/// Defines an implicit conversion of a <see cref="Memory{T}"/> to a <see cref="ReadOnlyMemory{T}"/>
/// </summary>
public static implicit operator ReadOnlyMemory<T>(Memory<T> memory) =>
Unsafe.As<Memory<T>, ReadOnlyMemory<T>>(ref memory);
/// <summary>
/// Returns an empty <see cref="Memory{T}"/>
/// </summary>
public static Memory<T> Empty => default;
/// <summary>
/// The number of items in the memory.
/// </summary>
public int Length => _length;
/// <summary>
/// Returns true if Length is 0.
/// </summary>
public bool IsEmpty => _length == 0;
/// <summary>
/// For <see cref="Memory{Char}"/>, returns a new instance of string that represents the characters pointed to by the memory.
/// Otherwise, returns a <see cref="string"/> with the name of the type and the number of elements.
/// </summary>
public override string ToString()
{
if (typeof(T) == typeof(char))
{
return (_object is string str) ? str.Substring(_index, _length) : Span.ToString();
}
#if FEATURE_UTF8STRING
else if (typeof(T) == typeof(Char8))
{
// TODO_UTF8STRING: Call into optimized transcoding routine when it's available.
Span<T> span = Span;
return Encoding.UTF8.GetString(new ReadOnlySpan<byte>(ref Unsafe.As<T, byte>(ref MemoryMarshal.GetReference(span)), span.Length));
}
#endif // FEATURE_UTF8STRING
return string.Format("System.Memory<{0}>[{1}]", typeof(T).Name, _length);
}
/// <summary>
/// Forms a slice out of the given memory, beginning at 'start'.
/// </summary>
/// <param name="start">The index at which to begin this slice.</param>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> index is not in range (&lt;0 or &gt;=Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Memory<T> Slice(int start)
{
if ((uint)start > (uint)_length)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
}
// It is expected for _index + start to be negative if the memory is already pre-pinned.
return new Memory<T>(_object, _index + start, _length - start);
}
/// <summary>
/// Forms a slice out of the given memory, beginning at 'start', of given length
/// </summary>
/// <param name="start">The index at which to begin this slice.</param>
/// <param name="length">The desired length for the slice (exclusive).</param>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in range (&lt;0 or &gt;=Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Memory<T> Slice(int start, int length)
{
#if BIT64
// See comment in Span<T>.Slice for how this works.
if ((ulong)(uint)start + (ulong)(uint)length > (ulong)(uint)_length)
ThrowHelper.ThrowArgumentOutOfRangeException();
#else
if ((uint)start > (uint)_length || (uint)length > (uint)(_length - start))
ThrowHelper.ThrowArgumentOutOfRangeException();
#endif
// It is expected for _index + start to be negative if the memory is already pre-pinned.
return new Memory<T>(_object, _index + start, length);
}
/// <summary>
/// Returns a span from the memory.
/// </summary>
public unsafe Span<T> Span
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get
{
// This property getter has special support for returning a mutable Span<char> that wraps
// an immutable String instance. This is obviously a dangerous feature and breaks type safety.
// However, we need to handle the case where a ReadOnlyMemory<char> was created from a string
// and then cast to a Memory<T>. Such a cast can only be done with unsafe or marshaling code,
// in which case that's the dangerous operation performed by the dev, and we're just following
// suit here to make it work as best as possible.
ref T refToReturn = ref Unsafe.AsRef<T>(null);
int lengthOfUnderlyingSpan = 0;
// Copy this field into a local so that it can't change out from under us mid-operation.
object? tmpObject = _object;
if (tmpObject != null)
{
if (typeof(T) == typeof(char) && tmpObject.GetType() == typeof(string))
{
// Special-case string since it's the most common for ROM<char>.
refToReturn = ref Unsafe.As<char, T>(ref Unsafe.As<string>(tmpObject).GetRawStringData());
lengthOfUnderlyingSpan = Unsafe.As<string>(tmpObject).Length;
}
#if FEATURE_UTF8STRING
else if ((typeof(T) == typeof(byte) || typeof(T) == typeof(Char8)) && tmpObject.GetType() == typeof(Utf8String))
{
refToReturn = ref Unsafe.As<byte, T>(ref Unsafe.As<Utf8String>(tmpObject).DangerousGetMutableReference());
lengthOfUnderlyingSpan = Unsafe.As<Utf8String>(tmpObject).Length;
}
#endif // FEATURE_UTF8STRING
else if (RuntimeHelpers.ObjectHasComponentSize(tmpObject))
{
// We know the object is not null, it's not a string, and it is variable-length. The only
// remaining option is for it to be a T[] (or a U[] which is blittable to T[], like int[]
// and uint[]). Otherwise somebody used private reflection to set this field, and we're not
// too worried about type safety violations at this point.
// 'tmpObject is T[]' below also handles things like int[] <-> uint[] being convertible
Debug.Assert(tmpObject is T[]);
refToReturn = ref Unsafe.As<byte, T>(ref Unsafe.As<T[]>(tmpObject).GetRawSzArrayData());
lengthOfUnderlyingSpan = Unsafe.As<T[]>(tmpObject).Length;
}
else
{
// We know the object is not null, and it's not variable-length, so it must be a MemoryManager<T>.
// Otherwise somebody used private reflection to set this field, and we're not too worried about
// type safety violations at that point. Note that it can't be a MemoryManager<U>, even if U and
// T are blittable (e.g., MemoryManager<int> to MemoryManager<uint>), since there exists no
// constructor or other public API which would allow such a conversion.
Debug.Assert(tmpObject is MemoryManager<T>);
Span<T> memoryManagerSpan = Unsafe.As<MemoryManager<T>>(tmpObject).GetSpan();
refToReturn = ref MemoryMarshal.GetReference(memoryManagerSpan);
lengthOfUnderlyingSpan = memoryManagerSpan.Length;
}
// If the Memory<T> or ReadOnlyMemory<T> instance is torn, this property getter has undefined behavior.
// We try to detect this condition and throw an exception, but it's possible that a torn struct might
// appear to us to be valid, and we'll return an undesired span. Such a span is always guaranteed at
// least to be in-bounds when compared with the original Memory<T> instance, so using the span won't
// AV the process.
nuint desiredStartIndex = (uint)_index & (uint)ReadOnlyMemory<T>.RemoveFlagsBitMask;
int desiredLength = _length;
#if BIT64
// See comment in Span<T>.Slice for how this works.
if ((ulong)desiredStartIndex + (ulong)(uint)desiredLength > (ulong)(uint)lengthOfUnderlyingSpan)
{
ThrowHelper.ThrowArgumentOutOfRangeException();
}
#else
if ((uint)desiredStartIndex > (uint)lengthOfUnderlyingSpan || (uint)desiredLength > (uint)(lengthOfUnderlyingSpan - desiredStartIndex))
{
ThrowHelper.ThrowArgumentOutOfRangeException();
}
#endif
refToReturn = ref Unsafe.Add(ref refToReturn, (IntPtr)(void*)desiredStartIndex);
lengthOfUnderlyingSpan = desiredLength;
}
return new Span<T>(ref refToReturn, lengthOfUnderlyingSpan);
}
}
/// <summary>
/// Copies the contents of the memory into the destination. If the source
/// and destination overlap, this method behaves as if the original values are in
/// a temporary location before the destination is overwritten.
///
/// <param name="destination">The Memory to copy items into.</param>
/// <exception cref="System.ArgumentException">
/// Thrown when the destination is shorter than the source.
/// </exception>
/// </summary>
public void CopyTo(Memory<T> destination) => Span.CopyTo(destination.Span);
/// <summary>
/// Copies the contents of the memory into the destination. If the source
/// and destination overlap, this method behaves as if the original values are in
/// a temporary location before the destination is overwritten.
///
/// <returns>If the destination is shorter than the source, this method
/// return false and no data is written to the destination.</returns>
/// </summary>
/// <param name="destination">The span to copy items into.</param>
public bool TryCopyTo(Memory<T> destination) => Span.TryCopyTo(destination.Span);
/// <summary>
/// Creates a handle for the memory.
/// The GC will not move the memory until the returned <see cref="MemoryHandle"/>
/// is disposed, enabling taking and using the memory's address.
/// <exception cref="System.ArgumentException">
/// An instance with nonprimitive (non-blittable) members cannot be pinned.
/// </exception>
/// </summary>
public unsafe MemoryHandle Pin()
{
// Just like the Span property getter, we have special support for a mutable Memory<char>
// that wraps an immutable String instance. This might happen if a caller creates an
// immutable ROM<char> wrapping a String, then uses Unsafe.As to create a mutable M<char>.
// This needs to work, however, so that code that uses a single Memory<char> field to store either
// a readable ReadOnlyMemory<char> or a writable Memory<char> can still be pinned and
// used for interop purposes.
// It's possible that the below logic could result in an AV if the struct
// is torn. This is ok since the caller is expecting to use raw pointers,
// and we're not required to keep this as safe as the other Span-based APIs.
object? tmpObject = _object;
if (tmpObject != null)
{
if (typeof(T) == typeof(char) && tmpObject is string s)
{
GCHandle handle = GCHandle.Alloc(tmpObject, GCHandleType.Pinned);
ref char stringData = ref Unsafe.Add(ref s.GetRawStringData(), _index);
return new MemoryHandle(Unsafe.AsPointer(ref stringData), handle);
}
#if FEATURE_UTF8STRING
else if ((typeof(T) == typeof(byte) || typeof(T) == typeof(Char8)) && tmpObject is Utf8String utf8String)
{
GCHandle handle = GCHandle.Alloc(tmpObject, GCHandleType.Pinned);
ref byte stringData = ref utf8String.DangerousGetMutableReference(_index);
return new MemoryHandle(Unsafe.AsPointer(ref stringData), handle);
}
#endif // FEATURE_UTF8STRING
else if (RuntimeHelpers.ObjectHasComponentSize(tmpObject))
{
// 'tmpObject is T[]' below also handles things like int[] <-> uint[] being convertible
Debug.Assert(tmpObject is T[]);
// Array is already pre-pinned
if (_index < 0)
{
void* pointer = Unsafe.Add<T>(Unsafe.AsPointer(ref Unsafe.As<T[]>(tmpObject).GetRawSzArrayData()), _index & ReadOnlyMemory<T>.RemoveFlagsBitMask);
return new MemoryHandle(pointer);
}
else
{
GCHandle handle = GCHandle.Alloc(tmpObject, GCHandleType.Pinned);
void* pointer = Unsafe.Add<T>(Unsafe.AsPointer(ref Unsafe.As<T[]>(tmpObject).GetRawSzArrayData()), _index);
return new MemoryHandle(pointer, handle);
}
}
else
{
Debug.Assert(tmpObject is MemoryManager<T>);
return Unsafe.As<MemoryManager<T>>(tmpObject).Pin(_index);
}
}
return default;
}
/// <summary>
/// Copies the contents from the memory into a new array. This heap
/// allocates, so should generally be avoided, however it is sometimes
/// necessary to bridge the gap with APIs written in terms of arrays.
/// </summary>
public T[] ToArray() => Span.ToArray();
/// <summary>
/// Determines whether the specified object is equal to the current object.
/// Returns true if the object is Memory or ReadOnlyMemory and if both objects point to the same array and have the same length.
/// </summary>
[EditorBrowsable(EditorBrowsableState.Never)]
public override bool Equals(object? obj)
{
if (obj is ReadOnlyMemory<T>)
{
return ((ReadOnlyMemory<T>)obj).Equals(this);
}
else if (obj is Memory<T> memory)
{
return Equals(memory);
}
else
{
return false;
}
}
/// <summary>
/// Returns true if the memory points to the same array and has the same length. Note that
/// this does *not* check to see if the *contents* are equal.
/// </summary>
public bool Equals(Memory<T> other)
{
return
_object == other._object &&
_index == other._index &&
_length == other._length;
}
/// <summary>
/// Serves as the default hash function.
/// </summary>
[EditorBrowsable(EditorBrowsableState.Never)]
public override int GetHashCode()
{
// We use RuntimeHelpers.GetHashCode instead of Object.GetHashCode because the hash
// code is based on object identity and referential equality, not deep equality (as common with string).
return (_object != null) ? HashCode.Combine(RuntimeHelpers.GetHashCode(_object), _index, _length) : 0;
}
}
}
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