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Allow reference types for pinned GC.AllocateArray() #89293

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merged 16 commits into from
Aug 11, 2023
+58 −36
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Allow reference types for pinned GC.AllocateArray() #89293

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d579879
Relaxing constraints of System.GC.AllocateArray<T>.
jthorborg Jul 21, 2023
5fc9157
Adding coverage of GC.AllocateArray with ref types.
jthorborg Jul 21, 2023
376fb89
Mono/NativeAOT relaxing of System.GC.AllocateArray<T>.
jthorborg Jul 21, 2023
808d582
Merge branch 'dotnet:main' into poh-allocate-array-allow-reference-types
jthorborg Jul 21, 2023
ea6de35
Relaxed GC.AllocateUninitializedArray for ref types as well.
jthorborg Jul 21, 2023
c403266
Simplifiy conditionals in AllocateUninitializedArray.
jthorborg Jul 21, 2023
30fd375
Also simplify path for NativeOAT.
jthorborg Jul 21, 2023
13fe7a1
Simplify pinning paths.
jthorborg Jul 21, 2023
3aeca6b
Revert mistake in prior refactor.
jthorborg Jul 21, 2023
2e502dc
Renaming in tests.
jthorborg Jul 21, 2023
d7dfad7
Update src/coreclr/System.Private.CoreLib/src/System/GC.CoreCLR.cs
jkotas Aug 2, 2023
3a1bca6
Apply suggestions from code review
jkotas Aug 2, 2023
4b805e5
Don't use `var` if type name doesn't exist explicitly on right-hand side
jthorborg Aug 10, 2023
f3aff36
PR feedback for using terse method tables and JIT intrinsics for GC a…
jthorborg Aug 10, 2023
349970a
Changed EmbeddedValueType and added comment.
jthorborg Aug 10, 2023
bfe62ec
Suggestions from PR feedback.
jthorborg Aug 11, 2023
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16 changes: 2 additions & 14 deletions src/coreclr/System.Private.CoreLib/src/System/GC.CoreCLR.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -732,9 +732,6 @@ internal static void UnregisterMemoryLoadChangeNotification(Action notification)
/// <typeparam name="T">Specifies the type of the array element.</typeparam>
/// <param name="length">Specifies the length of the array.</param>
/// <param name="pinned">Specifies whether the allocated array must be pinned.</param>
/// <remarks>
/// If pinned is set to true, <typeparamref name="T"/> must not be a reference type or a type that contains object references.
/// </remarks>
[MethodImpl(MethodImplOptions.AggressiveInlining)] // forced to ensure no perf drop for small memory buffers (hot path)
public static unsafe T[] AllocateUninitializedArray<T>(int length, bool pinned = false) // T[] rather than T?[] to match `new T[length]` behavior
{
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Expand All @@ -757,16 +754,13 @@ public static unsafe T[] AllocateUninitializedArray<T>(int length, bool pinned =

#endif
}
else if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
{
ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(T));
}

GC_ALLOC_FLAGS flags = GC_ALLOC_FLAGS.GC_ALLOC_ZEROING_OPTIONAL;
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if (pinned)
flags |= GC_ALLOC_FLAGS.GC_ALLOC_PINNED_OBJECT_HEAP;

return Unsafe.As<T[]>(AllocateNewArray(RuntimeTypeHandle.ToIntPtr(typeof(T[]).TypeHandle), length, flags));
// Runtime overrides GC_ALLOC_ZEROING_OPTIONAL if the type contains references, so we don't need to worry about that.
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return Unsafe.As<T[]>(AllocateNewArray(typeof(T[]).TypeHandle.Value, length, flags));
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Why did you change RuntimeTypeHandle.ToIntPtr to RuntimeTypeHandle.Value?

RuntimeTypeHandle.ToIntPtr is JIT intrinsic so it will be optimized to just loading a constant in most cases. RuntimeTypeHandle.Value does not have that optimization. This change may cause a perf regression.

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Oh! I had no idea it was an intrinsic, how is that discoverable?

I changed it to be identical to the similar usage just below: https://github.com/dotnet/runtime/pull/89293/files/d7dfad7341d828be78b09cbe1e49e696d09fac4c#diff-63ddcf9eb1f63c1ddef526934b79b086b1d30883f3293847bf966d047bc7666dR781

Perhaps the should instead revert this line and change the other to use the intrinsic?

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Oh! I had no idea it was an intrinsic, how is that discoverable?

JIT intrinsics are marked with [Intrinsic] attributes.

Perhaps the should instead revert this line and change the other to use the intrinsic?

Agree.

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Ok, I'll do the change once I get closure on the other discussion

}

/// <summary>
Expand All @@ -775,18 +769,12 @@ public static unsafe T[] AllocateUninitializedArray<T>(int length, bool pinned =
/// <typeparam name="T">Specifies the type of the array element.</typeparam>
/// <param name="length">Specifies the length of the array.</param>
/// <param name="pinned">Specifies whether the allocated array must be pinned.</param>
/// <remarks>
/// If pinned is set to true, <typeparamref name="T"/> must not be a reference type or a type that contains object references.
/// </remarks>
public static T[] AllocateArray<T>(int length, bool pinned = false) // T[] rather than T?[] to match `new T[length]` behavior
{
GC_ALLOC_FLAGS flags = GC_ALLOC_FLAGS.GC_ALLOC_NO_FLAGS;

if (pinned)
{
if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(T));

flags = GC_ALLOC_FLAGS.GC_ALLOC_PINNED_OBJECT_HEAP;
}

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13 changes: 0 additions & 13 deletions src/coreclr/nativeaot/System.Private.CoreLib/src/System/GC.NativeAot.cs
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Expand Up @@ -795,9 +795,6 @@ internal static ulong GetSegmentSize()
/// <typeparam name="T">Specifies the type of the array element.</typeparam>
/// <param name="length">Specifies the length of the array.</param>
/// <param name="pinned">Specifies whether the allocated array must be pinned.</param>
/// <remarks>
/// If pinned is set to true, <typeparamref name="T"/> must not be a reference type or a type that contains object references.
/// </remarks>
[MethodImpl(MethodImplOptions.AggressiveInlining)] // forced to ensure no perf drop for small memory buffers (hot path)
public static unsafe T[] AllocateUninitializedArray<T>(int length, bool pinned = false)
{
Expand All @@ -819,10 +816,6 @@ public static unsafe T[] AllocateUninitializedArray<T>(int length, bool pinned =
}
#endif
}
else if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
{
ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(T));
}

// kept outside of the small arrays hot path to have inlining without big size growth
return AllocateNewUninitializedArray(length, pinned);
Expand Down Expand Up @@ -851,18 +844,12 @@ static T[] AllocateNewUninitializedArray(int length, bool pinned)
/// <typeparam name="T">Specifies the type of the array element.</typeparam>
/// <param name="length">Specifies the length of the array.</param>
/// <param name="pinned">Specifies whether the allocated array must be pinned.</param>
/// <remarks>
/// If pinned is set to true, <typeparamref name="T"/> must not be a reference type or a type that contains object references.
/// </remarks>
public static unsafe T[] AllocateArray<T>(int length, bool pinned = false)
{
GC_ALLOC_FLAGS flags = GC_ALLOC_FLAGS.GC_ALLOC_NO_FLAGS;

if (pinned)
{
if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(T));

flags = GC_ALLOC_FLAGS.GC_ALLOC_PINNED_OBJECT_HEAP;
}

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49 changes: 45 additions & 4 deletions src/libraries/System.Runtime/tests/System/GCTests.cs
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Expand Up @@ -1058,11 +1058,52 @@ private static void AllocateArrayTooLarge()
Assert.Throws<OutOfMemoryException>(() => GC.AllocateUninitializedArray<double>(int.MaxValue, pinned: true));
}

[Fact]
private static void AllocateArrayRefType()
struct EmbeddedValueType<T>
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{
unsafe fixed byte _[7];
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Is there a specific reason for this? It looks like trying to fiddle with offsets and alignment. I tend to avoid these kind of mechanisms in tests without a comment as to the why.

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It was a simple way of increasing the size of the struct, making it less trivially laid out and requiring padding bits - to add a bit of confidence in we're not just overwriting the first set of bytes in a memory location.

We could add a comment or just remove it, it's not required.

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I think a non-generic struct like this would be sufficient for what you are trying to test here

private struct StructType
{
    internal object _;
    internal string _value;
    internal int _;
}

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public T Value;
}

[Theory]
[InlineData(false), InlineData(true)]
private static void AllocateArray_UninitializedOrNot_WithManagedType_DoesNotThrow(bool pinned)
{
void TryType<T>()
{
GC.AllocateUninitializedArray<T>(100, pinned);
GC.AllocateArray<T>(100, pinned);

GC.AllocateArray<EmbeddedValueType<T>>(100, pinned);
GC.AllocateUninitializedArray<EmbeddedValueType<T>>(100, pinned);
}

TryType<string>();
TryType<object>();
}

[Theory]
[InlineData(false), InlineData(true)]
private unsafe static void AllocateArrayPinned_ManagedValueType_CanRoundtripThroughPointer(bool uninitialized)
{
GC.AllocateUninitializedArray<string>(100);
Assert.Throws<ArgumentException>(() => GC.AllocateUninitializedArray<string>(100, pinned: true));
const int length = 100;
var rng = new Random(0xAF);

var array = uninitialized ? GC.AllocateUninitializedArray<EmbeddedValueType<string>>(length, pinned: true) : GC.AllocateArray<EmbeddedValueType<string>>(length, pinned: true);
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byte* pointer = (byte*)Unsafe.AsPointer(ref array[0]);
var size = Unsafe.SizeOf<EmbeddedValueType<string>>();

for(int i = 0; i < length; ++i)
{
var idx = rng.Next(length);
ref var evt = ref Unsafe.AsRef<EmbeddedValueType<string>>(pointer + size * idx);

var stringValue = rng.NextSingle().ToString();
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evt.Value = stringValue;

Assert.Equal(evt.Value, array[idx].Value);
}

GC.KeepAlive(array);
}

[Fact]
Expand Down
2 changes: 0 additions & 2 deletions src/mono/System.Private.CoreLib/src/System/GC.Mono.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -281,8 +281,6 @@ public static T[] AllocateUninitializedArray<T>(int length, bool pinned = false)
public static T[] AllocateArray<T>(int length, bool pinned = false)
{
if (pinned) {
if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(T));
return Unsafe.As<T[]>(AllocPinnedArray(typeof(T[]), length));
}

Expand Down