Module runtime 

High-performance graph-based stream processing runtime.

The runtime module provides the core execution engine for wavelet’s cooperative stream processing model. Built around a computation graph where nodes represent stream processors and edges define data dependencies, the runtime delivers deterministic, low-latency execution without the overhead of async runtimes or actor systems.

Architecture Overview

Computation Model

• Nodes: Stateful stream processors that transform data
• Relationships: Define when nodes should execute (Trigger vs Observe)
• Cooperative scheduling: Nodes voluntarily yield control after processing
• Dependency ordering: Execution follows graph topology (depth-first, scheduled first)
• Incremental computation: Only recompute when dependencies actually change

Core Components

Executor

The central execution engine that orchestrates:

• Graph topology management and node lifecycle
• Event-driven scheduling (I/O, timers, yields)
• Dependency-ordered execution cycles
• Garbage collection and resource cleanup

Node<T> and NodeBuilder<T>

Type-safe containers for node state with controlled mutation:

• Data-oriented design: Separate data (T) from behavior (cycle functions)
• Controlled mutation: Data changes only within cycle functions
• Builder pattern: Fluent API for configuring relationships and lifecycle

Runtime<C>

Complete runtime orchestration combining:

• Clock abstraction: Consistent time across execution cycles
• Execution modes: Different CPU/latency trade-offs (Spin, Park)
• Runtime loops: Automated execution patterns for different use cases

Event System

Unified event handling for external stimulus:

• I/O Events: Network sockets, file handles, external notifications
• Timer Events: Time-based scheduling with precise expiration
• Yield Events: Immediate re-scheduling for continued processing

Design Principles

Single-Threaded Cooperative Model

• Predictable performance: No hidden thread spawning or context switching
• Deterministic execution: Same inputs always produce the same execution order
• Zero-cost abstractions: Direct function calls without async overhead
• Resource control: Explicit management of CPU, memory, and I/O

Data-Oriented Design

• Type safety: Compile-time guarantees about node data types
• Memory efficiency: Minimal indirection and cache-friendly layouts
• Controlled mutation: Runtime coordinates when and how data changes
• Clear ownership: Data lifecycle tied to node lifecycle

Event-Driven Execution

• External integration: Clean interfaces to operating system events
• Backpressure handling: Natural flow control through graph topology
• Resource efficiency: Sleep when no work is available
• Low latency: Direct event dispatch without queueing overhead

Usage Patterns

Basic Stream Processing

use wavelet::runtime::*;

let mut executor = Executor::new();

// Create data source
let data_source = NodeBuilder::new(DataSource::new())
    .on_init(|executor, _, idx| {
        executor.yield_driver().yield_now(idx); // Start processing
    })
    .build(&mut executor, |source, ctx| {
        if let Some(data) = source.poll_data() {
            source.latest = data;
            Control::Broadcast // Notify downstream
        } else {
            Control::Unchanged
        }
    });

// Create processor that reacts to data
let processor = NodeBuilder::new(Processor::new())
    .triggered_by(&data_source)
    .build(&mut executor, |proc, ctx| {
        proc.process_data();
        Control::Unchanged
    });

// Run the graph
let runtime = RealtimeRuntime::new(ExecutionMode::Park);
runtime.run_forever();

I/O Integration

let (network_node, notifier) = NodeBuilder::new(NetworkHandler::new())
    .build_with_notifier(&mut executor, |handler, ctx| {
        match handler.socket.try_read(&mut handler.buffer) {
            Ok(0) => Control::Sweep, // Connection closed
            Ok(n) => {
                handler.process_bytes(n);
                Control::Broadcast
            }
            Err(e) if e.kind() == ErrorKind::WouldBlock => {
                // Re-register for readiness
                handler.reregister_interest(ctx);
                Control::Unchanged
            }
            Err(_) => Control::Sweep, // Connection error
        }
    })?;

// External thread can wake the network node
notifier.notify()?;

Dynamic Graph Construction

let spawner = NodeBuilder::new(DynamicSpawner::new())
    .build(&mut executor, |spawner, ctx| {
        if spawner.should_create_worker() {
            ctx.spawn_subgraph(|executor| {
                let worker = NodeBuilder::new(Worker::new())
                    .triggered_by(&spawner.work_queue)
                    .build(executor, process_work);
            });
        }
        Control::Unchanged
    });

Performance Characteristics

• Latency: Sub-microsecond node execution overhead
• Throughput: Millions of events per second on modern hardware
• Memory: Predictable allocation patterns, minimal runtime overhead
• CPU: Efficient utilization with configurable sleep/spin strategies
• Determinism: Consistent performance across runs with same inputs

Target Applications

The runtime excels in domains requiring:

• Financial systems: Low-latency trading, risk management, market data
• Real-time analytics: Live dashboards, alerting, stream aggregation
• IoT processing: Sensor data, device management, edge computing
• Protocol handling: Stateful network protocols, message parsing
• Media processing: Audio/video pipelines, real-time effects

For request/response workloads or applications requiring automatic parallelism, consider using async runtimes like Tokio alongside wavelet for the appropriate components of your system.

Re-exports

pub use clock::*;

pub use event_driver::*;

pub use executor::*;

pub use graph::*;

pub use node::*;

Modules

clock

event_driver

executor

graph

node

Structs

Runtime

A complete runtime instance that combines executor, clock, and execution mode.

Scheduler

SchedulerError

Enums

ExecutionMode

Execution mode for the real-time runtime.

Type Aliases

HistoricalRuntime

RealtimeRuntime

TestRuntime