What's new in .NET 9 and C# 13

This repo has a bunch of samples that show off new features in .NET 9.

.NET Aspire

NOTE: You're able to use .NET Aspire 9.0 with either .NET 8 or .NET 9!

• No longer needs the workload, Aspire is part of the SDK
• .NET Templates used to install project types

    dotnet new install Aspire.ProjectTemplates::9.0.0 --force

To create the sample project, run the following

    dotnet new aspire-starter --use-redis-cache --output Aspire

• New dashboard features
  • Manage resource lifecycles - stop, start, restart individual services
  • Combine telemetry from multiple sources (e.g. when a service has multiple instances)
  • Browser telemetry support (JavaScript OpenTelemetry SDK)
• Orchestration improvements
  • WaitFor(XYZ) : Wait for service XYZ to be ready before starting
  • WaitForCompletion(XYZ) : Wait for XYZ to complete before starting
• Resource health checks : .WithHttpHealthCheck("/health");
  • Will poll HealthCheck endpoint until it returns 200 OK
• Persistent Containers : .WithLifetime(ContainerLifetime.Persistent);
  • Will keep the container running during rebuilds of the app
• Container Networking : All services added to 'default-aspire-network' network
• Eventing Model : Hook into application lifecycle events
• Support for Azure Functions (preview)

Aspire Demo Notes

• Install the Aspire SDK
  • dotnet new install Aspire.ProjectTemplates::9.0.0 --force
• Create a new Aspire project
  • dotnet new aspire-starter --use-redis-cache --output Aspire
• Trust dev Certs
  • dotnet dev-certs https --trust
• Run the project dotnet run --project Aspire/Aspire.AppHost

Params Collections

Params now supports various collections beyond arrays, like Span<T> and ReadOnlySpan<T>.

So instead of this:

 // Method without using params
static void PrintNumbersWithSpan(ReadOnlySpan<int> numbers)
{
    Console.WriteLine("Using ReadOnlySpan<int> without params:");
    foreach (var number in numbers)
    {
        Console.WriteLine(number);
    }
}
PrintNumbersWithSpan(new ReadOnlySpan<int>(new[] { 6, 7, 8, 9, 10 }));

We can do this:

public void PrintNumbersWithSpan(params ReadOnlySpan<int> numbers)
{
    foreach (var number in numbers)
    {
        Console.WriteLine(number);
    }
}

PrintNumbersWithSpan(1, 2, 3, 4, 5);

To run the project

dotnet run --project ParamsDemo

Lock Object

Previously you could lock with an Object, but with .NET 9 there's a new Lock Object.

• Uses a new mechanism - Previously a Monitor class was used, but now uses the Dispose pattern.
• Asynchronous Limitations - You can't use the lock object with async methods, use the SemaphoreSlim class instead.

public class LockExample
{
    private readonly Lock _lock = new();

    public void DoStuff()
    {
        lock (_lock)
        {
            Console.WriteLine("We're inside .NET 9 lock");
        }
    }
}

To Run the project

dotnet run --project LockObj

Hybrid Cache

A new caching mechanism that combines in-memory (in-process) and distributed (out-of-process) caching. Designed to avoid problems like cache stampedes. It's still in preview, and will be relased in a future release of .NET 9.

Supports older versions, down to Framework v4.7.2, and Standard 2.0

To install; the Hybrid Cache package, run the following command.

    dotnet add package Microsoft.Extensions.Caching.Hybrid --version "9.0.0-preview.7.24406.2"

Stampede : When a cache expires, and multiple requests come in at the same time, they all hit the database at the same time.

For more info see : https://www.youtube.com/watch?v=PDIKTbbkmCk

New LINQ Methods : CountBy, AggregateBy, and Index

New Methods : Index, CountBy, AggregateBy

• Index - return the index of the element in the collection
• CountBy - groups the elements in the collection by a key and returns the count of elements in each group.
• AggregateBy - groups the elements in the collection by a key and returns the aggregate value of elements in each group.

To run the sample, run the following

dotnet run --project NewLinq

Built-in UUID v7 Generation

Previously .NET used the UUID v4 generation, but now you can use the UUID v7 generation, which keeps a timestamp in the UUID.

Importantly, these can be stored in a database, compatible with UniqueIdentifier

Timestamp	Random	More Random
48-bit timestamp	12-bit random	62-bit random

Guids (UUID4) look like this : 833dd2cd-f8d6-4688-8a43-769f06200874
UUID7 looks like this        : 0193b13d-4517-72f7-9866-20f4404cc050

To run the project run :

dotnet run --project NewUUID

Task.WhenEach()

If you had a list of Tasks and wanted to process each as soon as it completes, Task.WhenEach() is the method for you.

// List of 5 tasks that finish at random intervals
var tasks = Enumerable.Range(1, 5)
   .Select(async i =>
   {
     await Task.Delay(new Random().Next(1000, 5000));
     return $"Task {i} done";
   })
   .ToList();

// Before
while(tasks.Count > 0)
{
   var completedTask = await Task.WhenAny(tasks);
   tasks.Remove(completedTask);
   Console.WriteLine(await completedTask);
}

// .NET 9
await foreach (var completedTask in Task.WhenEach(tasks))
   Console.WriteLine(await completedTask);

To Run the project

dotnet run --project WhenEach

Performance Improvements

If you really want to blow your mind, go check out the performance blog release for .NET 9 at https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-9/.

This project runs a few benchmarks, incluing hashing, math functions and text manipulation across .Net 6. 8 and 9. It uses the BenchmarkDotNet library to run the benchmarks. To run the code run the following command.

dotnet run --project Performance -c Release --framework net6.0
dotnet run --project Performance -c Release --framework net8.0
dotnet run --project Performance -c Release --framework net9.0

Here are some of the results from the benchmarks.

.NET 6

---

Method	Mean	Error	StdDev	Median	Gen0	Gen1	Gen2	Allocated
LinqSum	7,614.06 ns	146.505 ns	425.037 ns	7,371.89 ns	0.0153	-	-	40 B
LinqOrderBySum	58,338.43 ns	228.745 ns	202.776 ns	58,265.73 ns	7.8125	-	-	12312 B
ComputeSha256	50,293.61 ns	125.765 ns	117.641 ns	50,321.76 ns	0.0610	-	-	112 B
ComputeMd5	22,755.18 ns	25.114 ns	23.492 ns	22,752.32 ns	0.0305	-	-	80 B
CalculateFibonacci	6,481,466.82 ns	20,222.151 ns	18,915.813 ns	6,482,283.59 ns	-	-	-	7 B
CalculatePrimes	391,165.61 ns	488.771 ns	381.600 ns	391,210.25 ns	-	-	-	-
ReverseString	46.69 ns	0.314 ns	0.294 ns	46.63 ns	0.1428	-	-	224 B
ReverseStringUsingSpan	39.95 ns	0.128 ns	0.100 ns	39.97 ns	0.0714	-	-	112 B
CountVowels	283.69 ns	2.725 ns	2.275 ns	282.95 ns	-	-	-	-
CountVowelsUsingSpan	282.51 ns	0.991 ns	0.878 ns	282.42 ns	-	-	-	-
JsonSerialization	313.53 ns	6.330 ns	11.086 ns	312.23 ns	0.1631	-	-	256 B
JsonDeserialization	797.71 ns	5.227 ns	4.890 ns	797.72 ns	0.1574	-	-	248 B
ThrowAndCatchException	7,698,602.08 ns	83,460.120 ns	78,068.648 ns	7,715,179.69 ns	218.7500	-	-	344008 B
GarbageCollectionTest	684,728.97 ns	3,663.886 ns	3,427.201 ns	684,608.84 ns	7000.0000	1000.0000	1000.0000	10480337 B
ParallelFor	543,406.26 ns	3,423.335 ns	3,202.190 ns	545,205.37 ns	0.9766	-	-	2438 B
TasksWithWhenAll	414,905.98 ns	2,185.347 ns	2,044.175 ns	414,877.29 ns	0.9766	-	-	1584 B
ThreadPoolBenchmarks	502,558.52 ns	4,034.446 ns	3,368.946 ns	501,736.82 ns	-	-	-	529 B

.NET 8

---

Method	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
LinqSum	109.43 ns	0.390 ns	0.345 ns	-	-	-	-
LinqOrderBySum	25,684.01 ns	147.426 ns	130.689 ns	7.8430	-	-	12312 B
ComputeSha256	50,412.54 ns	235.956 ns	209.169 ns	0.0610	-	-	112 B
ComputeMd5	22,736.64 ns	18.861 ns	14.725 ns	0.0305	-	-	80 B
CalculateFibonacci	3,386,988.50 ns	14,829.071 ns	13,145.585 ns	-	-	-	2 B
CalculatePrimes	371,194.93 ns	999.316 ns	885.867 ns	-	-	-	-
ReverseString	35.79 ns	0.258 ns	0.229 ns	0.1428	-	-	224 B
ReverseStringUsingSpan	27.13 ns	0.218 ns	0.204 ns	0.0714	-	-	112 B
CountVowels	164.22 ns	1.428 ns	1.266 ns	-	-	-	-
CountVowelsUsingSpan	162.22 ns	1.054 ns	0.986 ns	-	-	-	-
JsonSerialization	270.56 ns	5.338 ns	7.825 ns	0.0663	-	-	104 B
JsonDeserialization	674.63 ns	7.848 ns	6.127 ns	0.1574	-	-	248 B
ThrowAndCatchException	7,820,959.01 ns	134,955.796 ns	126,237.735 ns	218.7500	-	-	344003 B
GarbageCollectionTest	113,350.04 ns	2,211.646 ns	2,172.132 ns	1000.0000	1000.0000	1000.0000	200 B
ParallelFor	537,500.52 ns	796.256 ns	705.860 ns	0.9766	-	-	2272 B
TasksWithWhenAll	509,305.98 ns	6,182.510 ns	5,783.124 ns	0.9766	-	-	1585 B
ThreadPoolBenchmarks	491,315.57 ns	5,652.214 ns	5,287.085 ns	-	-	-	528 B

.NET 9

---

Method	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
LinqSum	107.89 ns	0.200 ns	0.187 ns	-	-	-	-
LinqOrderBySum	22,477.61 ns	97.449 ns	91.154 ns	7.8125	-	-	12280 B
ComputeSha256	50,380.23 ns	179.963 ns	159.532 ns	0.0610	-	-	112 B
ComputeMd5	22,759.29 ns	27.064 ns	25.315 ns	0.0305	-	-	80 B
CalculateFibonacci	3,603,892.29 ns	18,122.134 ns	16,951.455 ns	-	-	-	3 B
CalculatePrimes	365,074.52 ns	1,145.372 ns	1,071.382 ns	-	-	-	-
ReverseString	35.49 ns	0.218 ns	0.193 ns	0.1428	-	-	224 B
ReverseStringUsingSpan	27.52 ns	0.301 ns	0.281 ns	0.0714	-	-	112 B
CountVowels	161.98 ns	1.535 ns	1.361 ns	-	-	-	-
CountVowelsUsingSpan	146.90 ns	1.170 ns	1.037 ns	-	-	-	-
JsonSerialization	248.15 ns	5.035 ns	5.597 ns	0.0663	-	-	104 B
JsonDeserialization	506.49 ns	1.792 ns	1.496 ns	0.1574	-	-	248 B
ThrowAndCatchException	3,366,289.21 ns	66,375.332 ns	79,015.118 ns	203.1250	-	-	320000 B
GarbageCollectionTest	107,114.73 ns	2,061.475 ns	2,531.677 ns	1000.0000	1000.0000	1000.0000	171 B
ParallelFor	266,089.00 ns	681.617 ns	604.235 ns	0.9766	-	-	2264 B
TasksWithWhenAll	216,796.76 ns	2,697.630 ns	2,391.379 ns	0.9766	-	-	1577 B
ThreadPoolBenchmarks	418,913.97 ns	1,764.390 ns	1,473.346 ns	-	-	-	528 B

Aggregated Mean time (Smaller is better)

---

Test	.NET 6	.NET 8	.NET 9
LinqSum	7,525.14	109.33	107.95
LinqOrderBySum	57,681.18	23,880.68	22,798.88
ComputeSha256	50,267.66	50,304.02	50,927.69
ComputeMd5	22,743.14	22,733.03	22,762.04
CalculateFibonacci	6,380,681.08	3,401,143.61	3,602,688.88
CalculatePrimes	181,976,522.22	178,487,111.11	365,074.52
ReverseString	46.22	36.79	35.69
ReverseStringUsingSpan	39.7	28.06	27.44
CountVowels	288.64	164.62	168.21
CountVowelsUsingSpan	281.63	161.65	146.99
JsonSerialization	314.87	260.34	244.58
JsonDeserialization	785.04	715.33	504
ThrowAndCatchException	7,718,691.85	7,794,008.07	3,329,348.68
GarbageCollectionTest	664,636.39	114,326.03	105,293.09
ParallelFor	547,751.42	537,407.45	265,667.61
TasksWithWhenAll	418,350.52	506,076.28	214,791.19
ThreadPoolBenchmarks	503,761.47	414,715.03	215,313.97

Questions

• How many of you in the audience are using .NET 9?
• Do you go LTS to LTS or do you upgrade Release?
• Upgrade experience is very good!
  • Most of the time, just the CsProj + NuGet packages
  • Performance testing code above all uses exactly the same code
• The quality of the library with LTS and STS releases is the same, it's down to internal factors

References

• https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-13
• https://learn.microsoft.com/en-us/dotnet/aspire/whats-new/dotnet-aspire-9?tabs=windows
• https://medium.com/@dkorolov1/must-know-new-c-13-and-net-9-features-a42e5592e65b