FastCycloneDDS C# Bindings

A modern, high-performance, zero-allocation .NET binding for Eclipse Cyclone DDS, with idiomatic C# API.

See detailed technical overview.

Installation

Using the NuGet Package (Recommended)

Install the CycloneDDS.NET package from NuGet:

dotnet add package CycloneDDS.NET

This single package includes:

• Runtime Library: High-performance managed bindings.
• Native Assets: Pre-compiled ddsc.dll and idlc.exe (Windows x64).
• Build Tools: Automatic C# code generation during build.

Important: This package relies on native libraries that require the Visual C++ Redistributable for Visual Studio 2022 to be installed on the target system.

Working with Source Code

If you want to build the project from source or contribute:

1. Clone the repository (recursively, to get the native submodule):

   git clone --recursive https://github.com/pjanec/CycloneDds.NET.git
   cd CycloneDds.NET

2. Build and Test (One-Stop Script): Run the developer workflow script. This will automatically check for native artifacts (building them if missing), build the solution, and run all tests.

   .\build\build-and-test.ps1

3. Requirements:

   • .NET 8.0 SDK
   • Visual Studio 2022 (C++ Desktop Development workload) for native compilation.
   • CMake 3.16+ in your PATH.

Key Features

🚀 Performance Core

• Zero-Allocation Writes: Custom marshaller writes directly to pooled buffers (ArrayPool) using a C-compatible memory layout.
• Zero-Copy Reads: Read directly from native DDS buffers using ref struct views, bypassing deserialization.
• Unified API: Single reader provides both safe managed objects and high-performance zero-copy views.
• Lazy Deserialization: Only pay the cost of deep-copying objects when you explicitly access .Data.

🧬 Schema & Interoperability

• Code-First DSL: Define your data types entirely in C# using attributes ([DdsTopic], [DdsKey], [DdsStruct], [DdsQos]). No need to write IDL files manually.
• Automatic IDL Generation: The build tools automatically generate standard OMG IDL files from your C# classes, ensuring perfect interoperability with other DDS implementations (C++, Python, Java) and tools. See IDL Generation.
• Modern Language Integration: Full support for C# 12 [InlineArray] (safe fixed-size arrays without unsafe), typed enums (enum E : byte emits @bit_bound(8)), and default topic naming based on namespaces.
• Auto-Magic Type Discovery: Runtime automatically registers type descriptors based on your schema.
• IDL Import: Convert existing IDL files into C# DSL automatically using the IdlImporter tool.
• 100% Native Compliance: Uses Cyclone DDS native serializer for wire compatibility.

🛠️ Developer Experience

• Auto-Magic Type Discovery: No manual IDL compilation or type registration required.
• Async/Await: WaitDataAsync for non-blocking, task-based consumers.
• Client-Side Filtering: High-performance predicates (view => view.Id > 5) compiled to JIT code.
• Instance Management: O(1) history lookup for keyed topics.
• Sender Tracking: Identify the source application (Computer, PID, custom app id) of every message.
• Modern C#: Events, Properties, and generic constraints instead of listeners and pointers.

📡 Partitioning & Monitoring

• Partition Support: Isolate traffic using DDS partitions. Set a partition on a participant once and every reader/writer inherits it automatically, or override per-reader/writer with a named argument.
• Zero-Allocation WaitSet: Monitor 100+ readers on a single OS thread. DdsWaitSet.Wait(Span<IDdsReader>, timeout, ct) never allocates in the hot path and supports CancellationToken for instant, safe interruption.

---

1. Defining Data (The Schema)

Define your data using standard C# partial structs. The build tools generate the serialization logic automatically.

High-Performance Schema (Zero Alloc)

Use this for high-frequency data (1kHz+).

using CycloneDDS.Schema;

namespace Factory.Monitoring;

// Topic name defaults to namespace + class name ("Factory_Monitoring_SensorData") if omitted
[DdsTopic]
public partial struct SensorData
{
    [DdsKey, DdsId(0)]
    public int SensorId;

    [DdsId(1)]
    public double Value;

    // Fixed-size buffer (maps to char[32]). No heap allocation.
    [DdsId(2)]
    public FixedString32 LocationId; 

    // Safe, zero-allocation fixed array using C# 12 [InlineArray] (no 'unsafe' needed!)
    [DdsId(3)]
    public FloatBuffer8 Measurements;

    // Byte-backed enum yields IDL @bit_bound(8) automatically for optimal native network usage
    [DdsId(4)]
    public SensorStatus Status;
}

[System.Runtime.CompilerServices.InlineArray(8)]
public struct FloatBuffer8 { private float _element0; }

public enum SensorStatus : byte
{
    Offline,
    Online,
    Error
}

Unmanaged Schema (Unsafe Fixed Buffers)

For scenarios requiring direct memory manipulation or porting legacy C/C++ structs, you can use unsafe fixed arrays. The runtime maps these directly to native memory with zero allocation.

[DdsTopic("CustomTopicNameForVideoFrame")]
public unsafe partial struct VideoFrame
{
    [DdsKey]
    public int FrameId;

    // Classic C# unsafe fixed-size buffer
    public fixed byte Pixels[1920 * 1080 * 3];
}

Convenient Schema (Managed Types)

Use this for business logic where convenience outweighs raw speed.

[DdsStruct] // Helper struct to be used in the topic data struct (can be nested)
public partial struct GeoPoint { public double Lat; public double Lon; }

[DdsTopic("LogEvents")]
[DdsManaged] // Opt-in to GC allocations for the whole type
public partial struct LogEvent
{
    [DdsKey] 
    public int Id;

    // Standard string (Heap allocated)
    public string Message; 
    
    // Standard List (Heap allocated)
    public List<double> History;

    // Nested custom struct
    public GeoPoint Origin;
}

Configuration & QoS

You can define Quality of Service settings directly on the type using the [DdsQos] attribute. The Runtime automatically applies these settings when creating Writers and Readers for this topic.

[DdsTopic("MachineState")]
[DdsQos(
    Reliability = DdsReliability.Reliable,          // Guarantee delivery
    Durability = DdsDurability.TransientLocal,      // Late joiners get the last value
    HistoryKind = DdsHistoryKind.KeepLast,          // Keep only recent data
    HistoryDepth = 1                                // Only the latest sample
)]
public partial struct MachineState
{
    [DdsKey]
    public int MachineId;
    public StateEnum CurrentState;
}

---

2. Basic Usage

Publishing

using Factory.Monitoring;
using var participant = new DdsParticipant();

// Auto-discovers topic type and its default name ("Factory_Monitoring_SensorData")
using var writer = new DdsWriter<SensorData>(participant);

// Zero-allocation write path
var data = new SensorData 
{ 
    SensorId = 1, 
    Value = 25.5,
    LocationId = new FixedString32("Factory_A"),
    Status = SensorStatus.Online
};

// With C# 12, InlineArrays can be accessed directly by index
data.Measurements[0] = 1.0f; 

writer.Write(data);

Subscribing (Polling)

Reading uses a Scope pattern to ensure safety and zero-copy semantics. You "loan" the data, read it, and return it by disposing the scope.

using Factory.Monitoring;

using var reader = new DdsReader<SensorData>(participant);

// POLL FOR DATA
// Returns a "Loan" which manages native memory
using var loan = reader.Take(maxSamples: 10);

// Iterate received data
foreach (var sample in loan)
{
    // `sample.IsValid` indicates whether a full payload is present.
    // IMPORTANT: even when `ValidData == 0` (lifecycle/metadata-only samples),
    // the middleware provides the native memory with the topic key fields populated.
    // Therefore `sample.Data` is safe to call for every sample and will return
    // a managed object where key fields are set and non-key fields are defaulted.

    // Always obtain the managed copy (safe for metadata-only samples too)
    var data = sample.Data;

    if (sample.IsValid)
    {
        // OPTION A: Simple (Managed)
        // `data` is a full managed copy populated from native memory
        Console.WriteLine($"Received: {data.SensorId} = {data.Value}");
    }
    else
    {
        // Lifecycle event (e.g., instance disposed). Key fields are available in `data`.
        Console.WriteLine($"Instance {data.SensorId} state: {sample.Info.InstanceState}");
    }

    // OPTION B: Fast (Zero-Copy) — you can still use AsView() when you only need
    // transient, zero-allocation access to the native buffer (stack-only).
    // var view = sample.AsView();
}

---

3. Async/Await (Modern Loop)

Bridge the gap between real-time DDS and .NET Tasks. No blocking threads required.

Console.WriteLine("Waiting for data...");

// Efficiently waits using TaskCompletionSource (no polling loop)
while (await reader.WaitDataAsync())
{
    // Take all available data
    using var scope = reader.Take();
    
    foreach (var sample in scope)
    {
        await ProcessAsync(sample);
    }
}

---

4. Advanced Filtering

Filter data before you pay the cost of processing it. This implementation uses C# delegates but executes on the raw buffer view, allowing JIT optimizations to make it extremely fast.

// 1. Set a filter predicate on the Reader
// Logic executes during iteration, skipping irrelevant samples instantly.
// Since 'view' is a ref struct reading raw memory, this is Zero-Copy filtering.
reader.SetFilter(view => view.Value > 100.0 && view.LocationId.ToString() == "Lab_1");

// 2. Iterate
using var scope = reader.Take();
foreach (var highValueSample in scope)
{
    // Guaranteed to be > 100.0 and from Lab_1
}

// 3. Update filter dynamically at runtime
reader.SetFilter(null); // Clear filter

---

5. Instance Management (Keyed Topics)

For systems tracking many objects (fleets, tracks, sensors), efficiently query a specific object's history without iterating the entire database.

// 1. Create a key template for the object we care about
var key = new SensorData { SensorId = 5 };

// 2. Lookup the Handle (O(1) hashing)
DdsInstanceHandle handle = reader.LookupInstance(key);

if (!handle.IsNil)
{
    // 3. Read history for ONLY Sensor 5
    // Ignores Sensor 1, 2, 3... Zero iteration overhead.
    using var history = reader.ReadInstance(handle, maxSamples: 100);
    
    foreach (var snapshot in history)
    {
        Plot(snapshot.Value);
    }
}

---

6. Sender Tracking (Identity)

Identify exactly which application instance sent a message. Essential for multi-process debugging.

Sender Configuration

var config = new SenderIdentityConfig 
{ 
    AppDomainId = 1, 
    AppInstanceId = 100 
};

// Enable tracking BEFORE creating writers
participant.EnableSenderTracking(config);

// Now, every writer created by this participant automatically broadcasts identity
using var writer = new DdsWriter<LogEvent>(participant, "Logs");

Receiver Usage

// Enable tracking on the reader
reader.EnableSenderTracking(participant.SenderRegistry);

using var scope = reader.Take();
for (int i = 0; i < scope.Count; i++)
{
    // O(1) Lookup of sender info
    // Returns: ComputerName, ProcessName, ProcessId, AppDomainId, etc.
    var sender = scope.GetSender(i); 
    var msg = scope[i];

    if (sender != null)
    {
        Console.WriteLine($"[{sender.ComputerName} : PID {sender.ProcessId}] says: {msg.Message}");
    }
}

---

7. Status & Discovery

Know when peers connect or disconnect using standard C# Events.

// Writer Side
writer.PublicationMatched += (s, status) => 
{
    if (status.CurrentCountChange > 0)
        Console.WriteLine($"Subscriber connected! Total: {status.CurrentCount}");
    else
        Console.WriteLine("Subscriber lost.");
};

// Reliable Startup (Wait for Discovery)
// Solves the "Lost First Message" problem
await writer.WaitForReaderAsync(TimeSpan.FromSeconds(5));
writer.Write(new Message("Hello")); // Guaranteed to have a route

---

8. Lifecycle (Dispose & Unregister)

Properly manage the lifecycle of data instances in the Global Data Space.

var key = new SensorData { SensorId = 1 };

// 1. Data is invalid/deleted
// Readers receive InstanceState = NOT_ALIVE_DISPOSED
writer.DisposeInstance(key);

// 2. Writer is shutting down (graceful disconnect)
// Readers receive InstanceState = NOT_ALIVE_NO_WRITERS (if ownership exclusive)
writer.UnregisterInstance(key);

9. Partitions

DDS partitions let you divide a domain into named logical channels. Readers and writers only communicate within the same partition, making it easy to run multiple isolated subsystems on the same DDS domain (e.g. separate a monitoring plane from a control plane, or multiplex tenants).

Set a partition on the participant (inherited by all readers/writers)

// All readers and writers created from this participant will use "monitoring" automatically.
using var participant = new DdsParticipant(domainId: 0, defaultPartition: "monitoring");

// Topic name comes from [DdsTopic("SensorData")] — no need to repeat it.
using var reader = new DdsReader<SensorData>(participant);
using var writer = new DdsWriter<SensorData>(participant);

Override the partition per reader / writer

using var participant = new DdsParticipant(0, defaultPartition: "*"); // wildcard default

// This writer specifically targets the "control" partition.
using var controlWriter = new DdsWriter<SensorData>(
    participant, "SensorData", partition: "control");

// This reader stays on the default "*" partition — sees everything.
using var broadcastReader = new DdsReader<SensorData>(participant);

Resolution order

per-reader / per-writer partition  →  participant.DefaultPartition  →  (no partition)

---

10. WaitSet — Efficient Multi-Reader Monitoring

DdsWaitSet provides a native-backed mechanism for sleeping on many readers simultaneously on a single OS thread. This is ideal for monitoring applications that track 100+ topics and do not want the overhead of spawning a background Task per reader.

Basic usage

using var participant = new DdsParticipant(0, defaultPartition: "*");

// Create readers for every topic you want to monitor
using var tempReader    = new DdsReader<TemperatureEvent>(participant);
using var pressReader   = new DdsReader<PressureEvent>(participant);
using var statusReader  = new DdsReader<MachineStatus>(participant);

// Create WaitSet and attach all readers
using var waitset = new DdsWaitSet(participant);
waitset.Attach(tempReader);
waitset.Attach(pressReader);
waitset.Attach(statusReader);

// Pre-allocate result buffer once — no allocation inside the loop
IDdsReader[] triggered = new IDdsReader[16];

var cts = new CancellationTokenSource();

while (!cts.IsCancellationRequested)
{
    // Blocks until at least one reader has data, or the timeout expires, or ct is cancelled.
    // Zero allocation in this hot path.
    int count = waitset.Wait(triggered.AsSpan(), timeout: TimeSpan.FromSeconds(1), cts.Token);

    for (int i = 0; i < count; i++)
    {
        switch (triggered[i])
        {
            case DdsReader<TemperatureEvent> r:
                using (var loan = r.Take()) { /* handle temp */ }
                break;

            case DdsReader<PressureEvent> r:
                using (var loan = r.Take()) { /* handle pressure */ }
                break;

            case DdsReader<MachineStatus> r:
                using (var loan = r.Take()) { /* handle status */ }
                break;
        }
    }
}

Attach / Detach at runtime

Readers can be added or removed while the WaitSet is not waiting, making the monitored set dynamic:

// Start watching a new topic at runtime
var newReader = new DdsReader<AlarmEvent>(participant);
waitset.Attach(newReader);

// Stop watching (and dispose the reader when no longer needed)
waitset.Detach(newReader);
newReader.Dispose();

CancellationToken

Pass a CancellationToken to Wait to interrupt the blocking native call safely from any thread:

cts.Cancel(); // triggers the native guard condition, unblocks Wait() instantly

Performance characteristics

Operation	Allocation	Notes
Wait(...) hot path	0 Bytes	ArrayPool rent inside; result written into caller's Span
Attach / Detach	Small (one-time)	GCHandle + dictionary entry per reader
Cancellation callback	0 Bytes	Triggers native guard condition via P/Invoke

---

11. Legacy IDL Import

If you have existing DDS systems defined in IDL, you can generate the corresponding C# DSL automatically.

# Import IDL to C#
CycloneDDS.IdlImporter MySystem.idl ./src/Generated

This generates C# [DdsTopic] structs that are binary-compatible with your existing system. See IDL Import Guide for advanced usage including multi-module support.

---

Examples

Hello World

A complete "Hello World" example that demonstrates creating a topic, publishing, and subscribing in a single application can be found in examples/HelloWorld.

This example is designed to verify the NuGet package installation and basic functionality using the locally built package.

To run it:

1. Build the packages: .\build\pack.ps1
2. Run the example:

   cd examples/HelloWorld
   dotnet run

---

Dependencies

The CycloneDDS.NET package bundles these internal components:

• Managed Libraries: CycloneDDS.Core, CycloneDDS.Schema, CycloneDDS.CodeGen, CycloneDDS.Runtime
• Native Assets: ddsc.dll (Cyclone DDS), idlc.exe (IDL Compiler), cycloneddsidljson.dll (IDL JSON plugin)

Performance Characteristics

Feature	Allocation Cost	Performance Note
Write	0 Bytes	Uses ArrayPool + NativeArena
Read (View)	0 Bytes	Uses .AsView() + Ref Structs
Read (Managed)	Allocates	Uses .Data (Deep Copy)
Take (Polling)	0 Bytes	Uses Loaned Buffers
Filtering	0 Bytes	Manual loop filtering with Views
Sender Lookup	0 Bytes	O(1) Dictionary Lookup
Async Wait	~80 Bytes	One Task per await cycle
WaitSet.Wait	0 Bytes	Span output + ArrayPool rent; no heap in hot path

Built for speed. Designed for developers.