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Revert TraceContextPropagator performance refactor from 5749 (#6161)
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@stevejgordon
stevejgordon authored Mar 3, 2025
1 parent 577337c commit 1b555c1
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4 changes: 4 additions & 0 deletions src/OpenTelemetry.Api/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,10 @@ Notes](../../RELEASENOTES.md).

## Unreleased

* Revert optimize performance of `TraceContextPropagator.Extract` introduced
in #5749 to resolve #6158.
([#6161](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6161))

## 1.11.1

Released 2025-Jan-22
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136 changes: 24 additions & 112 deletions src/OpenTelemetry.Api/Context/Propagation/TraceContextPropagator.cs
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Original file line number Diff line number Diff line change
@@ -1,9 +1,9 @@
// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0

using System.Buffers;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Text;
using OpenTelemetry.Internal;

namespace OpenTelemetry.Context.Propagation;
Expand Down Expand Up @@ -76,7 +76,7 @@ public override PropagationContext Extract<T>(PropagationContext context, T carr
var tracestateCollection = getter(carrier, TraceState);
if (tracestateCollection?.Any() ?? false)
{
TryExtractTracestate(tracestateCollection, out tracestate);
TryExtractTracestate(tracestateCollection.ToArray(), out tracestate);
}

return new PropagationContext(
Expand Down Expand Up @@ -220,37 +220,31 @@ internal static bool TryExtractTraceparent(string traceparent, out ActivityTrace
return true;
}

internal static bool TryExtractTracestate(IEnumerable<string> tracestateCollection, out string tracestateResult)
internal static bool TryExtractTracestate(string[] tracestateCollection, out string tracestateResult)
{
tracestateResult = string.Empty;

char[]? rentedArray = null;
Span<char> traceStateBuffer = stackalloc char[128]; // 256B
Span<char> keyLookupBuffer = stackalloc char[96]; // 192B (3x32 keys)
int keys = 0;
int charsWritten = 0;

try
if (tracestateCollection != null)
{
foreach (var tracestateItem in tracestateCollection)
var keySet = new HashSet<string>();
var result = new StringBuilder();
for (int i = 0; i < tracestateCollection.Length; ++i)
{
var tracestate = tracestateItem.AsSpan();
int position = 0;

while (position < tracestate.Length)
var tracestate = tracestateCollection[i].AsSpan();
int begin = 0;
while (begin < tracestate.Length)
{
int length = tracestate.Slice(position).IndexOf(',');
int length = tracestate.Slice(begin).IndexOf(',');
ReadOnlySpan<char> listMember;

if (length != -1)
{
listMember = tracestate.Slice(position, length).Trim();
position += length + 1;
listMember = tracestate.Slice(begin, length).Trim();
begin += length + 1;
}
else
{
listMember = tracestate.Slice(position).Trim();
position = tracestate.Length;
listMember = tracestate.Slice(begin).Trim();
begin = tracestate.Length;
}

// https://github.com/w3c/trace-context/blob/master/spec/20-http_request_header_format.md#tracestate-header-field-values
Expand All @@ -261,7 +255,7 @@ internal static bool TryExtractTracestate(IEnumerable<string> tracestateCollecti
continue;
}

if (keys >= 32)
if (keySet.Count >= 32)
{
// https://github.com/w3c/trace-context/blob/master/spec/20-http_request_header_format.md#list
// test_tracestate_member_count_limit
Expand Down Expand Up @@ -292,107 +286,25 @@ internal static bool TryExtractTracestate(IEnumerable<string> tracestateCollecti
}

// ValidateKey() call above has ensured the key does not contain upper case letters.

var duplicationCheckLength = Math.Min(key.Length, 3);

if (keys > 0)
{
// Fast path check of first three chars for potential duplicated keys
var potentialMatchingKeyPosition = 1;
var found = false;
for (int i = 0; i < keys * 3; i += 3)
{
if (keyLookupBuffer.Slice(i, duplicationCheckLength).SequenceEqual(key.Slice(0, duplicationCheckLength)))
{
found = true;
break;
}

potentialMatchingKeyPosition++;
}

// If the fast check has found a possible duplicate, we need to do a full check
if (found)
{
var bufferToCompare = traceStateBuffer.Slice(0, charsWritten);

// We know which key is the first possible duplicate, so skip to that key
// by slicing to the position after the appropriate comma.
for (int i = 1; i < potentialMatchingKeyPosition; i++)
{
var commaIndex = bufferToCompare.IndexOf(',');

if (commaIndex > -1)
{
bufferToCompare.Slice(commaIndex);
}
}

int existingIndex = -1;
while ((existingIndex = bufferToCompare.IndexOf(key)) > -1)
{
if ((existingIndex > 0 && bufferToCompare[existingIndex - 1] != ',') || bufferToCompare[existingIndex + key.Length] != '=')
{
continue; // this is not a key
}

return false; // test_tracestate_duplicated_keys
}
}
}

// Store up to the first three characters of the key for use in the duplicate lookup fast path
var startKeyLookupIndex = keys > 0 ? keys * 3 : 0;
key.Slice(0, duplicationCheckLength).CopyTo(keyLookupBuffer.Slice(startKeyLookupIndex));

// Check we have capacity to write the key and value
var requiredCapacity = charsWritten > 0 ? listMember.Length + 1 : listMember.Length;

while (charsWritten + requiredCapacity > traceStateBuffer.Length)
if (!keySet.Add(key.ToString()))
{
GrowBuffer(ref rentedArray, ref traceStateBuffer);
// test_tracestate_duplicated_keys
return false;
}

if (charsWritten > 0)
if (result.Length > 0)
{
traceStateBuffer[charsWritten++] = ',';
result.Append(',');
}

listMember.CopyTo(traceStateBuffer.Slice(charsWritten));
charsWritten += listMember.Length;

keys++;
result.Append(listMember.ToString());
}
}

tracestateResult = traceStateBuffer.Slice(0, charsWritten).ToString();

return true;
tracestateResult = result.ToString();
}
finally
{
if (rentedArray is not null)
{
ArrayPool<char>.Shared.Return(rentedArray);
rentedArray = null;
}
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
static void GrowBuffer(ref char[]? array, ref Span<char> buffer)
{
var newBuffer = ArrayPool<char>.Shared.Rent(buffer.Length * 2);

buffer.CopyTo(newBuffer.AsSpan());

if (array is not null)
{
ArrayPool<char>.Shared.Return(array);
}

array = newBuffer;
buffer = array.AsSpan();
}
return true;
}

private static byte HexCharToByte(char c)
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