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System.Text.Json: stackalloc constants + misc PR feedback (#55350)
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* Follow-up feedback from #54186.

* Code review.

* Code review.

* Dedicated constant for the max number of chars permitted to be allocated on the stack.
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CodeBlanch committed Jul 18, 2021
1 parent c5edf0e commit f2a55e2
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Showing 33 changed files with 169 additions and 146 deletions.
6 changes: 3 additions & 3 deletions src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.TryGetProperty.cs
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Expand Up @@ -27,9 +27,9 @@ internal bool TryGetNamedPropertyValue(int index, ReadOnlySpan<char> propertyNam
int startIndex = index + DbRow.Size;
int endIndex = checked(row.NumberOfRows * DbRow.Size + index);

if (maxBytes < JsonConstants.StackallocThreshold)
if (maxBytes < JsonConstants.StackallocByteThreshold)
{
Span<byte> utf8Name = stackalloc byte[JsonConstants.StackallocThreshold];
Span<byte> utf8Name = stackalloc byte[JsonConstants.StackallocByteThreshold];
int len = JsonReaderHelper.GetUtf8FromText(propertyName, utf8Name);
utf8Name = utf8Name.Slice(0, len);

Expand Down Expand Up @@ -139,7 +139,7 @@ internal bool TryGetNamedPropertyValue(int index, ReadOnlySpan<byte> propertyNam
out JsonElement value)
{
ReadOnlySpan<byte> documentSpan = _utf8Json.Span;
Span<byte> utf8UnescapedStack = stackalloc byte[JsonConstants.StackallocThreshold];
Span<byte> utf8UnescapedStack = stackalloc byte[JsonConstants.StackallocByteThreshold];

// Move to the row before the EndObject
int index = endIndex - DbRow.Size;
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4 changes: 2 additions & 2 deletions src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.cs
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Expand Up @@ -298,8 +298,8 @@ internal bool TextEquals(int index, ReadOnlySpan<char> otherText, bool isPropert
byte[]? otherUtf8TextArray = null;

int length = checked(otherText.Length * JsonConstants.MaxExpansionFactorWhileTranscoding);
Span<byte> otherUtf8Text = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[JsonConstants.StackallocThreshold] :
Span<byte> otherUtf8Text = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(otherUtf8TextArray = ArrayPool<byte>.Shared.Rent(length));

ReadOnlySpan<byte> utf16Text = MemoryMarshal.AsBytes(otherText);
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7 changes: 5 additions & 2 deletions src/libraries/System.Text.Json/src/System/Text/Json/JsonConstants.cs
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Expand Up @@ -51,7 +51,8 @@ internal static class JsonConstants
public const int MaxWriterDepth = 1_000;
public const int RemoveFlagsBitMask = 0x7FFFFFFF;

public const int StackallocThreshold = 256;
public const int StackallocByteThreshold = 256;
public const int StackallocCharThreshold = StackallocByteThreshold / 2;

// In the worst case, an ASCII character represented as a single utf-8 byte could expand 6x when escaped.
// For example: '+' becomes '\u0043'
Expand All @@ -60,7 +61,7 @@ internal static class JsonConstants
public const int MaxExpansionFactorWhileEscaping = 6;

// In the worst case, a single UTF-16 character could be expanded to 3 UTF-8 bytes.
// Only surrogate pairs expand to 4 UTF-8 bytes but that is a transformation of 2 UTF-16 characters goign to 4 UTF-8 bytes (factor of 2).
// Only surrogate pairs expand to 4 UTF-8 bytes but that is a transformation of 2 UTF-16 characters going to 4 UTF-8 bytes (factor of 2).
// All other UTF-16 characters can be represented by either 1 or 2 UTF-8 bytes.
public const int MaxExpansionFactorWhileTranscoding = 3;

Expand Down Expand Up @@ -95,6 +96,8 @@ internal static class JsonConstants
public const int MinimumDateTimeParseLength = 10; // YYYY-MM-DD
public const int MaximumEscapedDateTimeOffsetParseLength = MaxExpansionFactorWhileEscaping * MaximumDateTimeOffsetParseLength;

public const int MaximumLiteralLength = 5; // Must be able to fit null, true, & false.

// Encoding Helpers
public const char HighSurrogateStart = '\ud800';
public const char HighSurrogateEnd = '\udbff';
Expand Down
8 changes: 4 additions & 4 deletions src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.Date.cs
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Expand Up @@ -51,8 +51,8 @@ public static bool TryParseAsISO(ReadOnlySpan<char> source, out DateTime value)

int maxLength = checked(source.Length * JsonConstants.MaxExpansionFactorWhileTranscoding);

Span<byte> bytes = maxLength <= JsonConstants.StackallocThreshold
? stackalloc byte[JsonConstants.StackallocThreshold]
Span<byte> bytes = maxLength <= JsonConstants.StackallocByteThreshold
? stackalloc byte[JsonConstants.StackallocByteThreshold]
: new byte[maxLength];

int length = JsonReaderHelper.GetUtf8FromText(source, bytes);
Expand Down Expand Up @@ -86,8 +86,8 @@ public static bool TryParseAsISO(ReadOnlySpan<char> source, out DateTimeOffset v

int maxLength = checked(source.Length * JsonConstants.MaxExpansionFactorWhileTranscoding);

Span<byte> bytes = maxLength <= JsonConstants.StackallocThreshold
? stackalloc byte[JsonConstants.StackallocThreshold]
Span<byte> bytes = maxLength <= JsonConstants.StackallocByteThreshold
? stackalloc byte[JsonConstants.StackallocByteThreshold]
: new byte[maxLength];

int length = JsonReaderHelper.GetUtf8FromText(source, bytes);
Expand Down
8 changes: 4 additions & 4 deletions src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.Escaping.cs
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Expand Up @@ -37,8 +37,8 @@ public static byte[] GetEscapedPropertyNameSection(ReadOnlySpan<byte> utf8Value,

int length = JsonWriterHelper.GetMaxEscapedLength(utf8Value.Length, firstEscapeIndexVal);

Span<byte> escapedValue = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> escapedValue = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(valueArray = ArrayPool<byte>.Shared.Rent(length));

JsonWriterHelper.EscapeString(utf8Value, escapedValue, firstEscapeIndexVal, encoder, out int written);
Expand All @@ -65,8 +65,8 @@ public static byte[] GetEscapedPropertyNameSection(ReadOnlySpan<byte> utf8Value,

int length = JsonWriterHelper.GetMaxEscapedLength(utf8Value.Length, firstEscapeIndexVal);

Span<byte> escapedValue = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> escapedValue = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(valueArray = ArrayPool<byte>.Shared.Rent(length));

JsonWriterHelper.EscapeString(utf8Value, escapedValue, firstEscapeIndexVal, encoder, out int written);
Expand Down
28 changes: 14 additions & 14 deletions src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.Unescaping.cs
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Expand Up @@ -14,8 +14,8 @@ public static bool TryGetUnescapedBase64Bytes(ReadOnlySpan<byte> utf8Source, int
{
byte[]? unescapedArray = null;

Span<byte> utf8Unescaped = utf8Source.Length <= JsonConstants.StackallocThreshold ?
stackalloc byte[utf8Source.Length] :
Span<byte> utf8Unescaped = utf8Source.Length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(unescapedArray = ArrayPool<byte>.Shared.Rent(utf8Source.Length));

Unescape(utf8Source, utf8Unescaped, idx, out int written);
Expand Down Expand Up @@ -44,8 +44,8 @@ public static string GetUnescapedString(ReadOnlySpan<byte> utf8Source, int idx)
int length = utf8Source.Length;
byte[]? pooledName = null;

Span<byte> utf8Unescaped = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> utf8Unescaped = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(pooledName = ArrayPool<byte>.Shared.Rent(length));

Unescape(utf8Source, utf8Unescaped, idx, out int written);
Expand All @@ -71,8 +71,8 @@ public static ReadOnlySpan<byte> GetUnescapedSpan(ReadOnlySpan<byte> utf8Source,
int length = utf8Source.Length;
byte[]? pooledName = null;

Span<byte> utf8Unescaped = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> utf8Unescaped = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(pooledName = ArrayPool<byte>.Shared.Rent(length));

Unescape(utf8Source, utf8Unescaped, idx, out int written);
Expand All @@ -96,8 +96,8 @@ public static bool UnescapeAndCompare(ReadOnlySpan<byte> utf8Source, ReadOnlySpa

byte[]? unescapedArray = null;

Span<byte> utf8Unescaped = utf8Source.Length <= JsonConstants.StackallocThreshold ?
stackalloc byte[utf8Source.Length] :
Span<byte> utf8Unescaped = utf8Source.Length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(unescapedArray = ArrayPool<byte>.Shared.Rent(utf8Source.Length));

Unescape(utf8Source, utf8Unescaped, 0, out int written);
Expand Down Expand Up @@ -127,12 +127,12 @@ public static bool UnescapeAndCompare(ReadOnlySequence<byte> utf8Source, ReadOnl

int length = checked((int)utf8Source.Length);

Span<byte> utf8Unescaped = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> utf8Unescaped = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(unescapedArray = ArrayPool<byte>.Shared.Rent(length));

Span<byte> utf8Escaped = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> utf8Escaped = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(escapedArray = ArrayPool<byte>.Shared.Rent(length));

utf8Source.CopyTo(utf8Escaped);
Expand Down Expand Up @@ -174,8 +174,8 @@ public static bool TryDecodeBase64(ReadOnlySpan<byte> utf8Unescaped, [NotNullWhe
{
byte[]? pooledArray = null;

Span<byte> byteSpan = utf8Unescaped.Length <= JsonConstants.StackallocThreshold ?
stackalloc byte[utf8Unescaped.Length] :
Span<byte> byteSpan = utf8Unescaped.Length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(pooledArray = ArrayPool<byte>.Shared.Rent(utf8Unescaped.Length));

OperationStatus status = Base64.DecodeFromUtf8(utf8Unescaped, byteSpan, out int bytesConsumed, out int bytesWritten);
Expand Down
6 changes: 3 additions & 3 deletions src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.cs
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Expand Up @@ -252,7 +252,7 @@ public static bool TryGetEscapedDateTime(ReadOnlySpan<byte> source, out DateTime
Debug.Assert(backslash != -1);

Debug.Assert(source.Length <= JsonConstants.MaximumEscapedDateTimeOffsetParseLength);
Span<byte> sourceUnescaped = stackalloc byte[source.Length];
Span<byte> sourceUnescaped = stackalloc byte[JsonConstants.MaximumEscapedDateTimeOffsetParseLength];

Unescape(source, sourceUnescaped, backslash, out int written);
Debug.Assert(written > 0);
Expand All @@ -277,7 +277,7 @@ public static bool TryGetEscapedDateTimeOffset(ReadOnlySpan<byte> source, out Da
Debug.Assert(backslash != -1);

Debug.Assert(source.Length <= JsonConstants.MaximumEscapedDateTimeOffsetParseLength);
Span<byte> sourceUnescaped = stackalloc byte[source.Length];
Span<byte> sourceUnescaped = stackalloc byte[JsonConstants.MaximumEscapedDateTimeOffsetParseLength];

Unescape(source, sourceUnescaped, backslash, out int written);
Debug.Assert(written > 0);
Expand All @@ -303,7 +303,7 @@ public static bool TryGetEscapedGuid(ReadOnlySpan<byte> source, out Guid value)
int idx = source.IndexOf(JsonConstants.BackSlash);
Debug.Assert(idx != -1);

Span<byte> utf8Unescaped = stackalloc byte[source.Length];
Span<byte> utf8Unescaped = stackalloc byte[JsonConstants.MaximumEscapedGuidLength];

Unescape(source, utf8Unescaped, idx, out int written);
Debug.Assert(written > 0);
Expand Down
4 changes: 2 additions & 2 deletions src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.MultiSegment.cs
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Expand Up @@ -540,9 +540,9 @@ private bool ConsumeLiteralMultiSegment(ReadOnlySpan<byte> literal, JsonTokenTyp

private bool CheckLiteralMultiSegment(ReadOnlySpan<byte> span, ReadOnlySpan<byte> literal, out int consumed)
{
Debug.Assert(span.Length > 0 && span[0] == literal[0]);
Debug.Assert(span.Length > 0 && span[0] == literal[0] && literal.Length <= JsonConstants.MaximumLiteralLength);

Span<byte> readSoFar = stackalloc byte[literal.Length];
Span<byte> readSoFar = stackalloc byte[JsonConstants.MaximumLiteralLength];
int written = 0;

long prevTotalConsumed = _totalConsumed;
Expand Down
6 changes: 3 additions & 3 deletions src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.cs
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Expand Up @@ -513,7 +513,7 @@ public bool ValueTextEquals(ReadOnlySpan<char> text)

int length = checked(text.Length * JsonConstants.MaxExpansionFactorWhileTranscoding);

if (length > JsonConstants.StackallocThreshold)
if (length > JsonConstants.StackallocByteThreshold)
{
otherUtf8TextArray = ArrayPool<byte>.Shared.Rent(length);
otherUtf8Text = otherUtf8TextArray;
Expand All @@ -523,8 +523,8 @@ public bool ValueTextEquals(ReadOnlySpan<char> text)
// Cannot create a span directly since it gets passed to instance methods on a ref struct.
unsafe
{
byte* ptr = stackalloc byte[JsonConstants.StackallocThreshold];
otherUtf8Text = new Span<byte>(ptr, JsonConstants.StackallocThreshold);
byte* ptr = stackalloc byte[JsonConstants.StackallocByteThreshold];
otherUtf8Text = new Span<byte>(ptr, JsonConstants.StackallocByteThreshold);
}
}

Expand Down
2 changes: 1 addition & 1 deletion ...System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/TimeSpanConverter.cs
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Expand Up @@ -54,7 +54,7 @@ public override TimeSpan Read(ref Utf8JsonReader reader, Type typeToConvert, Jso
int backslash = source.IndexOf(JsonConstants.BackSlash);
Debug.Assert(backslash != -1);

Span<byte> sourceUnescaped = stackalloc byte[source.Length];
Span<byte> sourceUnescaped = stackalloc byte[MaximumEscapedTimeSpanFormatLength];

JsonReaderHelper.Unescape(source, sourceUnescaped, backslash, out int written);
Debug.Assert(written > 0);
Expand Down
8 changes: 4 additions & 4 deletions ...ries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Bytes.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -139,8 +139,8 @@ private void WriteBase64EscapeProperty(ReadOnlySpan<char> propertyName, ReadOnly

int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);

Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
stackalloc char[length] :
Span<char> escapedPropertyName = length <= JsonConstants.StackallocCharThreshold ?
stackalloc char[JsonConstants.StackallocCharThreshold] :
(propertyArray = ArrayPool<char>.Shared.Rent(length));

JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
Expand All @@ -162,8 +162,8 @@ private void WriteBase64EscapeProperty(ReadOnlySpan<byte> utf8PropertyName, Read

int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);

Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> escapedPropertyName = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(propertyArray = ArrayPool<byte>.Shared.Rent(length));

JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
Expand Down
8 changes: 4 additions & 4 deletions ...s/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.DateTime.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -144,8 +144,8 @@ private void WriteStringEscapeProperty(ReadOnlySpan<char> propertyName, DateTime

int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);

Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
stackalloc char[length] :
Span<char> escapedPropertyName = length <= JsonConstants.StackallocCharThreshold ?
stackalloc char[JsonConstants.StackallocCharThreshold] :
(propertyArray = ArrayPool<char>.Shared.Rent(length));

JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
Expand All @@ -167,8 +167,8 @@ private void WriteStringEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, Date

int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);

Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> escapedPropertyName = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(propertyArray = ArrayPool<byte>.Shared.Rent(length));

JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
Expand Down
8 changes: 4 additions & 4 deletions ...em.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.DateTimeOffset.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -143,8 +143,8 @@ private void WriteStringEscapeProperty(ReadOnlySpan<char> propertyName, DateTime

int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);

Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
stackalloc char[length] :
Span<char> escapedPropertyName = length <= JsonConstants.StackallocCharThreshold ?
stackalloc char[JsonConstants.StackallocCharThreshold] :
(propertyArray = ArrayPool<char>.Shared.Rent(length));

JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
Expand All @@ -166,8 +166,8 @@ private void WriteStringEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, Date

int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);

Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> escapedPropertyName = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(propertyArray = ArrayPool<byte>.Shared.Rent(length));

JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
Expand Down
8 changes: 4 additions & 4 deletions ...es/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Decimal.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -143,8 +143,8 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<char> propertyName, decimal

int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);

Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
stackalloc char[length] :
Span<char> escapedPropertyName = length <= JsonConstants.StackallocCharThreshold ?
stackalloc char[JsonConstants.StackallocCharThreshold] :
(propertyArray = ArrayPool<char>.Shared.Rent(length));

JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
Expand All @@ -166,8 +166,8 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, deci

int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);

Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
stackalloc byte[length] :
Span<byte> escapedPropertyName = length <= JsonConstants.StackallocByteThreshold ?
stackalloc byte[JsonConstants.StackallocByteThreshold] :
(propertyArray = ArrayPool<byte>.Shared.Rent(length));

JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
Expand Down
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