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Make getting lazy properties on ServiceConfig threadsafe #1752

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Merged
merged 3 commits into from
May 20, 2022
Merged

Make getting lazy properties on ServiceConfig threadsafe #1752

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8dded46
Make getting lazy properties on ServiceConfig threadsafe
JamesNK May 19, 2022
fd1de75
Clean up
JamesNK May 19, 2022
0bf2077
Apply suggestions from code review
JamesNK May 19, 2022
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24 changes: 17 additions & 7 deletions src/Grpc.Net.Client/Internal/Configuration/ConfigProperty.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@

namespace Grpc.Net.Client.Internal.Configuration
{
internal struct ConfigProperty<TValue, TInner> where TValue : IConfigValue
internal sealed class ConfigProperty<TValue, TInner> where TValue : IConfigValue
{
private TValue? _value;
private readonly Func<TInner?, TValue?> _valueFactory;
Expand All @@ -37,13 +37,23 @@ public ConfigProperty(Func<TInner?, TValue?> valueFactory, string key)
{
if (_value == null)
{
var innerValue = inner.GetValue<TInner>(_key);
_value = _valueFactory(innerValue);

if (_value != null && innerValue == null)
// Multiple threads can get a property at the same time. We want this to be safe.
// Because a value could be lazily initialized, lock to ensure multiple threads
// don't try to update the underlying dictionary at the same time.
lock (this)
{
// Set newly created value
SetValue(inner, _value);
// Double-check locking.
if (_value == null)
{
var innerValue = inner.GetValue<TInner>(_key);
_value = _valueFactory(innerValue);
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@halter73 halter73 May 19, 2022 •
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I probably should have asked this before approving, but can _valueFactory call into user code? Or inner.GetValue/SetValue? This reminds me a little bit of the locks I took in ConfigurationManager that caused dotnet/runtime#61747.

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@JamesNK JamesNK May 19, 2022

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No, it's internal.


if (_value != null && innerValue == null)
{
// Set newly created value
SetValue(inner, _value);
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@BrennanConroy BrennanConroy May 19, 2022

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Should the SetValue function also lock since it's public and called by other code?

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@halter73 halter73 May 19, 2022

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ConfigProperty and IConfigValue are both internal so I think it's okay. If this was ever exposed anywhere, locking on this would be bad. But unless it's being exposed as object, I don't see how anyone would easily get a reference.

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@JamesNK JamesNK May 19, 2022

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Should the SetValue function also lock since it's public and called by other code?

The goal is to make the type thread-safe for reads, e.g. multiple threads can do this without error:

if (serviceConfig.LoadBalancingConfigs.Count > 0)
{
    // ....
}

If someone calls SetValue value by setting a property on another thread, e.g. serviceConfig.LoadBalancingConfigs = new List<LoadBalancingConfig>() then an error is fine.

}
}
}
}

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2 changes: 1 addition & 1 deletion src/Grpc.Net.Client/Internal/Configuration/Values.cs
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Expand Up @@ -20,7 +20,7 @@

namespace Grpc.Net.Client.Internal.Configuration
{
internal class Values<T, TInner> : IList<T>, IConfigValue
internal sealed class Values<T, TInner> : IList<T>, IConfigValue
{
internal readonly IList<TInner> Inner;

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2 changes: 1 addition & 1 deletion test/Grpc.Net.Client.Tests/Balancer/ConnectionManagerTests.cs
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Expand Up @@ -329,7 +329,7 @@ public async Task UpdateAddresses_ConnectIsInProgress_InProgressConnectIsCancele

private static ConnectionManager CreateConnectionManager(
ILoggerFactory loggerFactory,
TestResolver resolver,
Resolver resolver,
TestSubchannelTransportFactory transportFactory)
{
return new ConnectionManager(
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32 changes: 32 additions & 0 deletions test/Grpc.Net.Client.Tests/ServiceConfigTests.cs
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Expand Up @@ -137,6 +137,38 @@ public void LoadBalancingConfig_CreateUnderlyingConfig()
Assert.IsNotNull((IDictionary<string, object>)pickFirstConfig[LoadBalancingConfig.PickFirstPolicyName]);
}

[Test]
public async Task ServiceConfig_LoadBalancingConfigs_ConcurrentAccess()
{
// Arrange & Act
for (var i = 0; i < 100; i++)
{
await AccessServiceConfigConcurrently();
}
}

private static async Task AccessServiceConfigConcurrently()
{
var serviceConfig = new ServiceConfig();

List<Task> connectTasks = new List<Task>();
for (var i = 0; i < 100; i++)
{
connectTasks.Add(Task.Run(ConnectAsync));
}

await Task.WhenAll(connectTasks);

void ConnectAsync()
{
// Excuse to access LoadBalancingConfigs
if (serviceConfig.LoadBalancingConfigs.Count > 0)
{
serviceConfig.ToString();
}
}
}

[Test]
public void LoadBalancingConfig_ReadUnderlyingConfig()
{
Expand Down