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Ensure delayed initialization of JsonArray/JsonObject is thread-safe #77567

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Oct 28, 2022
Merged

Ensure delayed initialization of JsonArray/JsonObject is thread-safe #77567

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5389266
Ensure delayed initialization of JsonArray/JsonObject is thread-safe
eiriktsarpalis Oct 27, 2022
ffebcb1
Address feedback
eiriktsarpalis Oct 27, 2022
7b86a84
Add null check before invoking delayed initializers
eiriktsarpalis Oct 28, 2022
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53 changes: 34 additions & 19 deletions src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonArray.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Text.Json.Serialization.Converters;
using System.Threading;

namespace System.Text.Json.Nodes
{
Expand Down Expand Up @@ -85,7 +86,7 @@ private void InitializeFromArray(JsonNode?[] items)
throw new InvalidOperationException(SR.Format(SR.NodeElementWrongType, nameof(JsonValueKind.Array)));
}

internal JsonArray (JsonElement element, JsonNodeOptions? options = null) : base(options)
internal JsonArray(JsonElement element, JsonNodeOptions? options = null) : base(options)
{
Debug.Assert(element.ValueKind == JsonValueKind.Array);
_jsonElement = element;
Expand Down Expand Up @@ -180,33 +181,47 @@ public override void WriteTo(Utf8JsonWriter writer, JsonSerializerOptions? optio

private void CreateNodes()
{
if (_list == null)
if (_list is null)
{
List<JsonNode?> list;
CreateNodesCore();
}

if (_jsonElement == null)
{
list = new List<JsonNode?>();
}
else
{
JsonElement jElement = _jsonElement.Value;
Debug.Assert(jElement.ValueKind == JsonValueKind.Array);
void CreateNodesCore()
{
// Even though _list initialization can be subject to races,
// ensure that contending threads use a coherent view of jsonElement.

// Because JsonElement cannot be read atomically there might be torn reads,
// however the order of read/write operations guarantees that that's only
// possible if the value of _list is non-null.
JsonElement? jsonElement = _jsonElement;
Interlocked.MemoryBarrier();
List<JsonNode?>? list = _list;

list = new List<JsonNode?>(jElement.GetArrayLength());
if (list is null)
{
list = new();

foreach (JsonElement element in jElement.EnumerateArray())
if (jsonElement.HasValue)
{
JsonNode? node = JsonNodeConverter.Create(element, Options);
node?.AssignParent(this);
list.Add(node);
JsonElement jElement = jsonElement.Value;
Debug.Assert(jElement.ValueKind == JsonValueKind.Array);

list = new List<JsonNode?>(jElement.GetArrayLength());

foreach (JsonElement element in jElement.EnumerateArray())
{
JsonNode? node = JsonNodeConverter.Create(element, Options);
node?.AssignParent(this);
list.Add(node);
}
}

// Clear since no longer needed.
// Ensure _jsonElement is written to after _list
_list = list;
Interlocked.MemoryBarrier();
_jsonElement = null;
}

_list = list;
}
}

Expand Down
46 changes: 31 additions & 15 deletions src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonObject.IDictionary.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
using System.Collections.Generic;
using System.Diagnostics;
using System.Text.Json.Serialization.Converters;
using System.Threading;

namespace System.Text.Json.Nodes
{
Expand Down Expand Up @@ -261,32 +262,47 @@ IEnumerator IEnumerable.GetEnumerator()

private void InitializeIfRequired()
{
if (_dictionary != null)
if (_dictionary is null)
{
return;
InitializeCore();
}

bool caseInsensitive = Options.HasValue ? Options.Value.PropertyNameCaseInsensitive : false;
var dictionary = new JsonPropertyDictionary<JsonNode?>(caseInsensitive);
if (_jsonElement.HasValue)
void InitializeCore()
{
JsonElement jElement = _jsonElement.Value;
// Even though _dictionary initialization can be subject to races,
// ensure that contending threads use a coherent view of jsonElement.

// Because JsonElement cannot be read atomically there might be torn reads,
// however the order of read/write operations guarantees that that's only
// possible if the value of _dictionary is non-null.
JsonElement? jsonElement = _jsonElement;
Interlocked.MemoryBarrier();
JsonPropertyDictionary<JsonNode?>? dictionary = _dictionary;

foreach (JsonProperty jElementProperty in jElement.EnumerateObject())
if (dictionary is null)
{
JsonNode? node = JsonNodeConverter.Create(jElementProperty.Value, Options);
if (node != null)
bool caseInsensitive = Options.HasValue ? Options.Value.PropertyNameCaseInsensitive : false;
dictionary = new JsonPropertyDictionary<JsonNode?>(caseInsensitive);
if (jsonElement.HasValue)
{
node.Parent = this;
foreach (JsonProperty jElementProperty in jsonElement.Value.EnumerateObject())
{
JsonNode? node = JsonNodeConverter.Create(jElementProperty.Value, Options);
if (node != null)
{
node.Parent = this;
}

dictionary.Add(new KeyValuePair<string, JsonNode?>(jElementProperty.Name, node));
}
}

dictionary.Add(new KeyValuePair<string, JsonNode?>(jElementProperty.Name, node));
// Ensure _jsonElement is written to after _dictionary
_dictionary = dictionary;
Interlocked.MemoryBarrier();
_jsonElement = null;
}

_jsonElement = null;
}

_dictionary = dictionary;
}
}
}
13 changes: 13 additions & 0 deletions src/libraries/System.Text.Json/tests/System.Text.Json.Tests/JsonNode/JsonArrayTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Xunit;

namespace System.Text.Json.Nodes.Tests
Expand Down Expand Up @@ -473,5 +474,17 @@ public static void GetJsonArrayIEnumerable()
Assert.True(jArrayEnumerator.MoveNext());
Assert.Equal("value", ((JsonValue)jArrayEnumerator.Current).GetValue<string>());
}

[Fact]
public static void LazyInitializationIsThreadSafe()
{
string arrayText = "[\"elem0\",\"elem1\"]";
JsonArray node = Assert.IsType<JsonArray>(JsonNode.Parse(arrayText));
Parallel.For(0, 128, i =>
{
Assert.Equal("elem0", (string)node[0]);
Assert.Equal("elem1", (string)node[1]);
});
}
}
}
13 changes: 13 additions & 0 deletions src/libraries/System.Text.Json/tests/System.Text.Json.Tests/JsonNode/JsonObjectTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
using System.IO;
using System.Linq;
using System.Text.Json.Serialization.Tests;
using System.Threading.Tasks;
using Xunit;

namespace System.Text.Json.Nodes.Tests
Expand Down Expand Up @@ -956,5 +957,17 @@ static void Test(JsonObject jObject)
Assert.Equal("World", (string)jObject["hello"]); // Test case insensitivity
}
}

[Fact]
public static void LazyInitializationIsThreadSafe()
{
string arrayText = "{\"prop0\":0,\"prop1\":1}";
JsonObject jObj = Assert.IsType<JsonObject>(JsonNode.Parse(arrayText));
Parallel.For(0, 128, i =>
{
Assert.Equal(0, (int)jObj["prop0"]);
Assert.Equal(1, (int)jObj["prop1"]);
});
}
}
}