lifecycle

lifecycle is a Go library for managing application shutdown signals and interactive terminal I/O robustly. It centralizes the "Dual Signal" logic and "Interruptible I/O" patterns originally extracted from Trellis and designed for any tool needing robust signal handling.

Vision

To be the standard Control Plane for Infrastructure-Aware Applications (Services, Agents, CLIs).

• v1 (Foundation): Solves "Death Management" (Signals, Blocking I/O, Zombies).
• v2 (Evolution): Solves "Life Management" (Events, Reactions, Hot Reloading).

Project Status & Versioning

Important

v2.x (Current): Introduces the Application Control Plane, generalizing "Signals" into "Events" (Hot Reload, Health Checks, Input Commands).

v1.x (Stable - LTS): Focuses strictly on Death Management (Graceful Shutdown, Signals, Leak Prevention).

Installation

go get github.com/aretw0/lifecycle

Features (Foundation v1)

• SignalContext: Differentiates between SIGINT (User Interrupt) and SIGTERM (System Shutdown).
  • Configurable Thresholds: Support for "Industry Standard" (Cancel on 1st), "Escalation" (Cancel on Nth), and "Unsafe" (No auto-kill) modes.
  • SIGTERM: Always triggers immediate graceful shutdown (context cancellation).
• TermIO:
  • InterruptibleReader: Wraps io.Reader to allow Read() calls to be abandoned when a context is cancelled (avoids goroutine leaks).
  • Platform Aware: Automatically uses CONIN$ on Windows.
    • Why? On Windows, standard os.Stdin closes immediately upon receiving a signal (like Ctrl+C), causing a fatal EOF before the application can gracefully handle the signal. lifecycle switches to CONIN$, which keeps the handle open, allowing the SignalContext to process the event.
  • UpgradeTerminal: Helper to upgrade an arbitrary existing io.Reader (if it identifies as a terminal) to the safe platform-specific reader.
• Observability & Introspection:
  • Unified Dashboard: SystemDiagram synthesizes Signal and Worker states into a single Mermaid visualization.
  • Rich Metrics: Built-in providers for tracking shutdown health, data loss, and shutdown latency.
  • Stall Detection: Automatically detects and warns if a shutdown hook is stalled (runs > 5s).
• Reliability Primitives (v1.4):
  • Critical Sections: lifecycle.Do(ctx, fn) shields atomic operations from cancellation and returns any error from the protected function.
  • Introspection: SignalContext.Reason() to differentiate between "Manual Stop", "Interrupt", or "Timeout".
• Worker & Supervisor (v1.3):
  • Unified Interface: Standard Start, Stop, Wait contract for Processes, Goroutines, and Containers.
  • Supervision Tree: Supervisor manages hierarchical worker clusters with restart policies (OneForOne, OneForAll).
  • Dynamic Topology: Add or remove workers at runtime.
  • Functional Workers: Turn any Go function into a managed Worker.
  • Process Hygiene: Automatic cleanup of child processes if the parent dies (Job Objects/PDeathSig).
  • Handover Protocol: Standardized environment variables (LIFECYCLE_RESUME_ID, LIFECYCLE_PREV_EXIT) to pass context across restarts.
  • Container Abstraction: Generic interface to manage containerized workloads without direct SDK dependencies.
• DX Helpers (v1.4 & v2.0):
  • Run: One-line main entry point with options (WithLogger, WithMetrics).
  • NewInteractiveRouter: Pre-configured router for CLIs (Signals + Input + Commands).
  • Sleep: Context-aware sleep (returns immediately on cancel).
  • OnShutdown: Type-safe hook registration without casting.

Roadmap (Control Plane v2)

• Event Router: Generalize Signals into Events (Webhook, FileWatch, HealthCheck).
• Managed Concurrency: lifecycle.Go(ctx, fn) for non-leaking goroutines.
• Reactions: Reload, Suspend, Scale alongside Shutdown.

Managed Concurrency (v2.0 Preview)

lifecycle now provides primitives to manage goroutines safely, ensuring they respect shutdown signals and provide visibility.

lifecycle.Run(func(ctx context.Context) error {
    // Fire-and-forget but tracked and panic-safe
    lifecycle.Go(ctx, func(ctx context.Context) error {
        // ...
        return nil
    })
    return nil
})

Quick Start (The Golden Path)

For 99% of CLI applications, you just need lifecycle.Run. It handles signals, context cancellation, and cleanup automatically.

package main

import (
    "context"
    "fmt"
    "time"
    "github.com/aretw0/lifecycle"
)

func main() {
    // 1. Wrap your logic in a Job
    // 2. lifecycle.Run manages the boring "Death Management" stuff
    lifecycle.Run(lifecycle.Job(func(ctx context.Context) error {
        fmt.Println("App started. Press Ctrl+C to exit.")
        
        // 3. Use lifecycle.Go to spawn safe, tracked background tasks
        lifecycle.Go(ctx, func(ctx context.Context) error {
            // This goroutine is automatically waited for on shutdown
            // Panics are caught and logged, preventing crashes
            select {
            case <-ctx.Done():
                return nil
            case <-time.After(5 * time.Second):
                fmt.Println("Task complete")
                return nil
            }
        })

        // 4. Wait for interrupt
        <-ctx.Done()
        fmt.Println("Shutting down...")
        return nil
    }))
}

Basic Patterns (CLI & Automation)

1. Robust Input (Windows Safe)

Reading from Stdin on Windows is tricky. lifecycle solves the "Ctrl+C kills the prompt" problem by automatically using CONIN$.

// Smart Open (handles Windows CONIN$)
reader, _ := lifecycle.OpenTerminal()
defer reader.Close()

// Wrap to respect context cancellation (prevents blocked Read calls)
r := lifecycle.NewInterruptibleReader(reader, ctx.Done())

buf := make([]byte, 1024)
n, err := r.Read(buf)
if lifecycle.IsInterrupted(err) {
    return // Clean exit
}

2. Graceful Hooks

Register cleanup functions that run after the context is cancelled but before the process exits.

lifecycle.OnShutdown(ctx, func() {
    db.Close()
    fmt.Println("Cleanup done locally")
})

Advanced Patterns (Control Plane v2)

For complex long-running services/agents that need dynamic behavior (Hot Reload, Supervisors).

1. Managed Concurrency & Global Fallback

lifecycle.Go(ctx, fn) is designed to work within lifecycle.Run. However, if you use it in a standalone script, it safely falls back to a Global Task Tracker.

func main() {
    ctx := context.Background()
    
    // Works safely even without lifecycle.Run
    lifecycle.Go(ctx, func(ctx context.Context) error {
        // ...
        return nil
    })
    
    // Explicitly wait for global tasks (required without Run)
    lifecycle.WaitForGlobal()
}

2. Supervisor & Workers

Manage long-running processes, containers, or goroutines with restarts and hygiene.

// Create a Supervisor with a "OneForOne" restart strategy
sup := lifecycle.NewSupervisor("agent", lifecycle.SupervisorStrategyOneForOne,
    lifecycle.NewProcessWorker("pinger", "ping", "1.1.1.1"),
    lifecycle.NewWorkerFromFunc("metrics", metricsLoop),
)

sup.Start(ctx)
<-ctx.Done()
sup.Stop(context.Background())

3. System Introspection

Generate live architecture diagrams of your running application.

// Generate Mermaid Dashboard
diagram := lifecycle.SystemDiagram(ctx.State(), supervisor.State())
fmt.Println(diagram)

Metrics Palette

The library uses a consistent color palette for all generated diagrams:

• 🟡 Pending: Defined but not yet active.
• 🔵 Running: Active and healthy.
• 🟢 Stopped: Successfully terminated.
• 🔴 Failed: Crashed or terminated with error.

I/O Safety

The library implements Context-Aware I/O to balance data preservation and responsiveness:

• Read() (Pipeline Safe): Uses a Shielded Return strategy. If data arrives simultaneously with a cancellation signal, it returns the data (nil error). This guarantees no data loss in pipelines or logs.
• ReadInteractive() (Interactive Safe): Uses a Strict Discard strategy. If the user hits Ctrl+C while typing, any partial input is discarded to prevent accidental execution of commands.

Documentation

• PRODUCT: Vision & Mission.
• TECHNICAL: Architecture & Design (with Diagrams).
• PLANNING: Roadmap & Backlog.