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JsonSerializer.DeserializeAsyncEnumerable should not wait until buffer is filled. #70430

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merged 1 commit into from
Jun 10, 2022
Merged

JsonSerializer.DeserializeAsyncEnumerable should not wait until buffer is filled. #70430

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168 changes: 23 additions & 145 deletions ...braries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Stream.cs
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Original file line number Diff line number Diff line change
@@ -1,14 +1,12 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Buffers;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Runtime.CompilerServices;
using System.Text.Json.Serialization;
using System.Text.Json.Serialization.Converters;
using System.Text.Json.Serialization.Metadata;
using System.Threading;
using System.Threading.Tasks;
Expand Down Expand Up @@ -375,7 +373,7 @@ public static partial class JsonSerializer
}

JsonTypeInfo jsonTypeInfo = options.GetOrAddJsonTypeInfoForRootType(typeof(TValue));
return CreateAsyncEnumerableDeserializer<TValue>(utf8Json, jsonTypeInfo, cancellationToken);
return CreateAsyncEnumerableDeserializer(utf8Json, CreateQueueTypeInfo<TValue>(jsonTypeInfo), cancellationToken);
}

/// <summary>
Expand Down Expand Up @@ -406,36 +404,38 @@ public static partial class JsonSerializer
ThrowHelper.ThrowArgumentNullException(nameof(jsonTypeInfo));
}

return CreateAsyncEnumerableDeserializer<TValue>(utf8Json, jsonTypeInfo, cancellationToken);
return CreateAsyncEnumerableDeserializer(utf8Json, CreateQueueTypeInfo<TValue>(jsonTypeInfo), cancellationToken);
}

private static JsonTypeInfo<Queue<TValue>> CreateQueueTypeInfo<TValue>(JsonTypeInfo jsonTypeInfo)
{
return JsonMetadataServices.CreateQueueInfo<Queue<TValue>, TValue>(
options: jsonTypeInfo.Options,
collectionInfo: new()
{
ObjectCreator = static () => new Queue<TValue>(),
ElementInfo = jsonTypeInfo,
NumberHandling = jsonTypeInfo.Options.NumberHandling
});
}

private static async IAsyncEnumerable<TValue> CreateAsyncEnumerableDeserializer<TValue>(
Stream utf8Json,
JsonTypeInfo jsonTypeInfo,
JsonTypeInfo<Queue<TValue>> queueTypeInfo,
[EnumeratorCancellation] CancellationToken cancellationToken)
{
JsonSerializerOptions options = jsonTypeInfo.Options;
JsonTypeInfo<Queue<TValue>> queueTypeInfo =
JsonMetadataServices.CreateQueueInfo<Queue<TValue>, TValue>(
options: options,
collectionInfo: new()
{
ObjectCreator = () => new Queue<TValue>(),
ElementInfo = jsonTypeInfo,
NumberHandling = options.NumberHandling
});

queueTypeInfo.EnsureConfigured();
JsonSerializerOptions options = queueTypeInfo.Options;
var bufferState = new ReadBufferState(options.DefaultBufferSize);
ReadStack readStack = default;
queueTypeInfo.EnsureConfigured();
readStack.Initialize(queueTypeInfo, supportContinuation: true);
var jsonReaderState = new JsonReaderState(options.GetReaderOptions());

try
{
do
{
bufferState = await ReadFromStreamAsync(utf8Json, bufferState, cancellationToken).ConfigureAwait(false);
bufferState = await bufferState.ReadFromStreamAsync(utf8Json, cancellationToken, fillBuffer: false).ConfigureAwait(false);
ContinueDeserialize<Queue<TValue>>(
ref bufferState,
ref jsonReaderState,
Expand Down Expand Up @@ -476,7 +476,7 @@ private static async IAsyncEnumerable<TValue> CreateAsyncEnumerableDeserializer<
{
while (true)
{
bufferState = await ReadFromStreamAsync(utf8Json, bufferState, cancellationToken).ConfigureAwait(false);
bufferState = await bufferState.ReadFromStreamAsync(utf8Json, cancellationToken).ConfigureAwait(false);
TValue value = ContinueDeserialize<TValue>(ref bufferState, ref jsonReaderState, ref readStack, converter, options);

if (bufferState.IsFinalBlock)
Expand Down Expand Up @@ -507,7 +507,7 @@ private static async IAsyncEnumerable<TValue> CreateAsyncEnumerableDeserializer<
{
while (true)
{
bufferState = ReadFromStream(utf8Json, bufferState);
bufferState.ReadFromStream(utf8Json);
TValue value = ContinueDeserialize<TValue>(ref bufferState, ref jsonReaderState, ref readStack, converter, options);

if (bufferState.IsFinalBlock)
Expand All @@ -522,146 +522,24 @@ private static async IAsyncEnumerable<TValue> CreateAsyncEnumerableDeserializer<
}
}

/// <summary>
/// Read from the stream until either our buffer is filled or we hit EOF.
/// Calling ReadCore is relatively expensive, so we minimize the number of times
/// we need to call it.
/// </summary>
internal static async ValueTask<ReadBufferState> ReadFromStreamAsync(
Stream utf8Json,
ReadBufferState bufferState,
CancellationToken cancellationToken)
{
while (true)
{
int bytesRead = await utf8Json.ReadAsync(
#if BUILDING_INBOX_LIBRARY
bufferState.Buffer.AsMemory(bufferState.BytesInBuffer),
#else
bufferState.Buffer, bufferState.BytesInBuffer, bufferState.Buffer.Length - bufferState.BytesInBuffer,
#endif
cancellationToken).ConfigureAwait(false);

if (bytesRead == 0)
{
bufferState.IsFinalBlock = true;
break;
}

bufferState.BytesInBuffer += bytesRead;

if (bufferState.BytesInBuffer == bufferState.Buffer.Length)
{
break;
}
}

return bufferState;
}

/// <summary>
/// Read from the stream until either our buffer is filled or we hit EOF.
/// Calling ReadCore is relatively expensive, so we minimize the number of times
/// we need to call it.
/// </summary>
internal static ReadBufferState ReadFromStream(
Stream utf8Json,
ReadBufferState bufferState)
{
while (true)
{
int bytesRead = utf8Json.Read(
#if BUILDING_INBOX_LIBRARY
bufferState.Buffer.AsSpan(bufferState.BytesInBuffer));
#else
bufferState.Buffer, bufferState.BytesInBuffer, bufferState.Buffer.Length - bufferState.BytesInBuffer);
#endif

if (bytesRead == 0)
{
bufferState.IsFinalBlock = true;
break;
}

bufferState.BytesInBuffer += bytesRead;

if (bufferState.BytesInBuffer == bufferState.Buffer.Length)
{
break;
}
}

return bufferState;
}

internal static TValue ContinueDeserialize<TValue>(
ref ReadBufferState bufferState,
ref JsonReaderState jsonReaderState,
ref ReadStack readStack,
JsonConverter converter,
JsonSerializerOptions options)
{
if (bufferState.BytesInBuffer > bufferState.ClearMax)
{
bufferState.ClearMax = bufferState.BytesInBuffer;
}

int start = 0;
if (bufferState.IsFirstIteration)
{
bufferState.IsFirstIteration = false;

// Handle the UTF-8 BOM if present
Debug.Assert(bufferState.Buffer.Length >= JsonConstants.Utf8Bom.Length);
if (bufferState.Buffer.AsSpan().StartsWith(JsonConstants.Utf8Bom))
{
start += JsonConstants.Utf8Bom.Length;
bufferState.BytesInBuffer -= JsonConstants.Utf8Bom.Length;
}
}

// Process the data available
TValue value = ReadCore<TValue>(
ref jsonReaderState,
bufferState.IsFinalBlock,
new ReadOnlySpan<byte>(bufferState.Buffer, start, bufferState.BytesInBuffer),
bufferState.Bytes,
options,
ref readStack,
converter);

Debug.Assert(readStack.BytesConsumed <= bufferState.BytesInBuffer);
int bytesConsumed = checked((int)readStack.BytesConsumed);

bufferState.BytesInBuffer -= bytesConsumed;

// The reader should have thrown if we have remaining bytes.
Debug.Assert(!bufferState.IsFinalBlock || bufferState.BytesInBuffer == 0);

if (!bufferState.IsFinalBlock)
{
// Check if we need to shift or expand the buffer because there wasn't enough data to complete deserialization.
if ((uint)bufferState.BytesInBuffer > ((uint)bufferState.Buffer.Length / 2))
{
// We have less than half the buffer available, double the buffer size.
byte[] oldBuffer = bufferState.Buffer;
int oldClearMax = bufferState.ClearMax;
byte[] newBuffer = ArrayPool<byte>.Shared.Rent((bufferState.Buffer.Length < (int.MaxValue / 2)) ? bufferState.Buffer.Length * 2 : int.MaxValue);

// Copy the unprocessed data to the new buffer while shifting the processed bytes.
Buffer.BlockCopy(oldBuffer, bytesConsumed + start, newBuffer, 0, bufferState.BytesInBuffer);
bufferState.Buffer = newBuffer;
bufferState.ClearMax = bufferState.BytesInBuffer;

// Clear and return the old buffer
new Span<byte>(oldBuffer, 0, oldClearMax).Clear();
ArrayPool<byte>.Shared.Return(oldBuffer);
}
else if (bufferState.BytesInBuffer != 0)
{
// Shift the processed bytes to the beginning of buffer to make more room.
Buffer.BlockCopy(bufferState.Buffer, bytesConsumed + start, bufferState.Buffer, 0, bufferState.BytesInBuffer);
}
}
Debug.Assert(readStack.BytesConsumed <= bufferState.Bytes.Length);
bufferState.AdvanceBuffer((int)readStack.BytesConsumed);

return value;
}
Expand Down
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