org.sonar.plugins.csharp.S6612.html Maven / Gradle / Ivy
Why is this an issue?
When using the ConcurrentDictionary, there are many overloads of the GetOrAdd and AddOrUpdate methods that
take both a TKey argument and a lambda that expects a TKey parameter. This means that the right side of the lambda can be
written using either the lambda’s parameter or the method’s argument. However, using the method’s argument leads to the lambda capturing it, and the
compiler will need to generate a class and instantiate it before the call. This means memory allocations, as well as more time spend during Garbage
Collection.
What is the potential impact?
We measured a significant improvement both in execution time and memory allocation. For more details see the Benchmarks section from
the More info tab.
How to fix it
When you are using the ConcurrentDictionary methods GetOrAdd or AddOrUpdate, reference the key by using the
lambda’s parameter instead of the method’s one.
Code examples
Noncompliant code example
int UpdateValue(ConcurrentDictionary<int, int> dict, int key) =>
dict.GetOrAdd(key, _ => key + 42);
Compliant solution
int UpdateValue(ConcurrentDictionary<int, int> dict, int key) =>
dict.GetOrAdd(key, x => x + 42);
Resources
Documentation
Benchmarks
Method
Runtime
Mean
Standard Deviation
Allocated
Capture
.NET 7.0
68.52 ms
4.450 ms
88000063 B
Lambda
.NET 7.0
39.29 ms
3.712 ms
50 B
Capture
.NET Framework 4.6.2
74.58 ms
5.199 ms
88259787 B
Lambda
.NET Framework 4.6.2
42.03 ms
2.752 ms
-
Glossary
The results were generated by running the following snippet with BenchmarkDotNet:
private ConcurrentDictionary<int, string> dict;
private List<int> data;
[Params(1_000_000)]
public int N { get; set; }
[GlobalSetup]
public void Setup()
{
dict = new ConcurrentDictionary<int, string>();
data = Enumerable.Range(0, N).OrderBy(_ => Guid.NewGuid()).ToList();
}
[Benchmark(baseline=true)]
public void Capture()
{
foreach (var guid in data)
{
dict.GetOrAdd(guid, _ => $"{guid}"); // "guid" is captured
}
}
[Benchmark]
public void Lambda()
{
foreach (var guid in data)
{
dict.GetOrAdd(guid, x => $"{x}"); // no capture
}
}
Hardware configuration:
BenchmarkDotNet=v0.13.5, OS=Windows 10 (10.0.19045.2846/22H2/2022Update)
11th Gen Intel Core i7-11850H 2.50GHz, 1 CPU, 16 logical and 8 physical cores
.NET SDK=7.0.203
[Host] : .NET 7.0.5 (7.0.523.17405), X64 RyuJIT AVX2
.NET 7.0 : .NET 7.0.5 (7.0.523.17405), X64 RyuJIT AVX2
.NET Framework 4.6.2 : .NET Framework 4.8.1 (4.8.9139.0), X64 RyuJIT VectorSize=256