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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.
using System.Runtime.InteropServices;
namespace System.Buffers
{
/// <summary>
/// Contains factory methods to create <see cref="BoundedMemory{T}"/> instances.
/// </summary>
public static partial class BoundedMemory
{
/// <summary>
/// Allocates a new <see cref="BoundedMemory{T}"/> region which is immediately preceded by
/// or immediately followed by a poison (MEM_NOACCESS) page. If <paramref name="placement"/>
/// is <see cref="PoisonPagePlacement.Before"/>, then attempting to read the memory
/// immediately before the returned <see cref="BoundedMemory{T}"/> will result in an AV.
/// If <paramref name="placement"/> is <see cref="PoisonPagePlacement.After"/>, then
/// attempting to read the memory immediately after the returned <see cref="BoundedMemory{T}"/>
/// will result in AV.
/// </summary>
/// <remarks>
/// The newly-allocated memory will be populated with random data.
/// </remarks>
public static BoundedMemory<T> Allocate<T>(int elementCount, PoisonPagePlacement placement = PoisonPagePlacement.After) where T : unmanaged
{
if (elementCount < 0)
{
throw new ArgumentOutOfRangeException(nameof(elementCount));
}
if (placement != PoisonPagePlacement.Before && placement != PoisonPagePlacement.After)
{
throw new ArgumentOutOfRangeException(nameof(placement));
}
var retVal = AllocateWithoutDataPopulation<T>(elementCount, placement);
FillRandom(MemoryMarshal.AsBytes(retVal.Span));
return retVal;
}
/// <summary>
/// Similar to <see cref="Allocate(int, PoisonPagePlacement)"/>, but populates the allocated
/// native memory block from existing data rather than using random data.
/// </summary>
public static BoundedMemory<T> AllocateFromExistingData<T>(ReadOnlySpan<T> data, PoisonPagePlacement placement = PoisonPagePlacement.After) where T : unmanaged
{
if (placement != PoisonPagePlacement.Before && placement != PoisonPagePlacement.After)
{
throw new ArgumentOutOfRangeException(nameof(placement));
}
var retVal = AllocateWithoutDataPopulation<T>(data.Length, placement);
data.CopyTo(retVal.Span);
return retVal;
}
/// <summary>
/// Similar to <see cref="Allocate(int, PoisonPagePlacement)"/>, but populates the allocated
/// native memory block from existing data rather than using random data.
/// </summary>
public static BoundedMemory<T> AllocateFromExistingData<T>(T[] data, PoisonPagePlacement placement = PoisonPagePlacement.After) where T : unmanaged
{
return AllocateFromExistingData(new ReadOnlySpan<T>(data), placement);
}
private static void FillRandom(Span<byte> buffer)
{
// Loop over a Random instance manually since Random.NextBytes(Span<byte>) doesn't
// exist on all platforms we target.
Random random = new Random(); // doesn't need to be cryptographically strong
for (int i = 0; i < buffer.Length; i++)
{
buffer[i] = (byte)random.Next();
}
}
private static BoundedMemory<T> AllocateWithoutDataPopulation<T>(int elementCount, PoisonPagePlacement placement) where T : unmanaged
{
if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
{
return AllocateWithoutDataPopulationWindows<T>(elementCount, placement);
}
else
{
return AllocateWithoutDataPopulationUnix<T>(elementCount, placement);
}
}
}
}
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