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|
// Package fanout distributes values from a single input channel to multiple output channels.
package fanout
import (
"context"
"errors"
"fmt"
"sync"
"sync/atomic"
)
// FanOutObserver defines callbacks for monitoring fan-out lifecycle events.
type FanOutObserver interface {
OnDistribute()
OnOutputClosed()
}
// FanOutStrategy defines how values are distributed across output channels.
type FanOutStrategy int
const (
// RoundRobin distributes values evenly across output channels in rotation.
RoundRobin FanOutStrategy = iota
// Broadcast sends each value to all output channels.
Broadcast
)
// ErrInvalidStrategy is returned when an unknown FanOutStrategy is provided.
var ErrInvalidStrategy = errors.New("fanout: unknown distribution strategy")
// FanOutConfig holds configuration options for creating a FanOut instance.
type FanOutConfig struct {
WorkerCount int
BufferSize int
Strategy FanOutStrategy
Observer FanOutObserver
}
// Option is a functional option for configuring a FanOut instance.
type Option func(*FanOutConfig)
// FanOut distributes values from a single input channel to multiple output channels.
type FanOut[T any] struct {
cfg *FanOutConfig
outputs []chan T
running atomic.Bool
cachedOutputs []<-chan T
once sync.Once
}
// NewFanOut creates a new FanOut instance with the provided options.
func NewFanOut[T any](opts ...Option) (*FanOut[T], error) {
cfg := &FanOutConfig{
WorkerCount: 1,
BufferSize: 0,
Observer: nil,
Strategy: RoundRobin,
}
for _, opt := range opts {
opt(cfg)
}
if cfg.WorkerCount < 1 {
return nil, fmt.Errorf("fanout: worker count must be at least 1, got %d", cfg.WorkerCount)
}
if cfg.BufferSize < 0 {
return nil, fmt.Errorf("fanout: buffer size must not be negative, got %d", cfg.BufferSize)
}
if cfg.Strategy != RoundRobin && cfg.Strategy != Broadcast {
return nil, ErrInvalidStrategy
}
outputs := make([]chan T, cfg.WorkerCount)
for i := range outputs {
outputs[i] = make(chan T, cfg.BufferSize)
}
return &FanOut[T]{
cfg: cfg,
outputs: outputs,
}, nil
}
// Run starts distributing values from the input channel to all output channels.
func (f *FanOut[T]) Run(ctx context.Context, input <-chan T) {
if input == nil {
panic("fanout: input channel must not be nil")
}
if !f.running.CompareAndSwap(false, true) {
panic("fanout: Run() called multiple times")
}
go func() {
idx := 0
defer f.running.Store(false)
defer f.closeAllOutput()
for {
select {
case value, ok := <-input:
if !ok {
return
}
switch f.cfg.Strategy {
case RoundRobin:
f.roundRobin(ctx, value, &idx)
case Broadcast:
f.broadcast(ctx, value)
}
case <-ctx.Done():
return
}
}
}()
}
// Outputs returns receive-only channel references for the distributed streams.
func (f *FanOut[T]) Outputs() []<-chan T {
f.once.Do(func() {
f.cachedOutputs = make([]<-chan T, len(f.outputs))
for i, ch := range f.outputs {
f.cachedOutputs[i] = ch
}
})
return f.cachedOutputs
}
func safeObserve(fn func()) {
defer func() { recover() }()
fn()
}
func (f *FanOut[T]) roundRobin(ctx context.Context, value T, index *int) {
target := *index % f.cfg.WorkerCount
select {
case f.outputs[target] <- value:
*index = (*index + 1) % f.cfg.WorkerCount
if f.cfg.Observer != nil {
safeObserve(f.cfg.Observer.OnDistribute)
}
case <-ctx.Done():
return
}
}
func (f *FanOut[T]) broadcast(ctx context.Context, value T) {
var wg sync.WaitGroup
for _, ch := range f.outputs {
wg.Go(func() {
select {
case ch <- value:
if f.cfg.Observer != nil {
safeObserve(f.cfg.Observer.OnDistribute)
}
case <-ctx.Done():
return
}
})
}
wg.Wait()
}
func (f *FanOut[T]) closeAllOutput() {
for _, ch := range f.outputs {
close(ch)
}
if f.cfg.Observer != nil {
safeObserve(f.cfg.Observer.OnOutputClosed)
}
}
// WithWorkerCount sets the number of output channels for the fan-out.
func WithWorkerCount(n int) Option {
return func(cfg *FanOutConfig) {
cfg.WorkerCount = n
}
}
// WithBufferSize sets the buffer capacity for each output channel.
func WithBufferSize(size int) Option {
return func(cfg *FanOutConfig) {
cfg.BufferSize = size
}
}
// WithStrategy sets the distribution strategy for the fan-out.
func WithStrategy(strategy FanOutStrategy) Option {
return func(cfg *FanOutConfig) {
cfg.Strategy = strategy
}
}
// WithObserver attaches a FanOutObserver to receive lifecycle event callbacks.
func WithObserver(observer FanOutObserver) Option {
return func(cfg *FanOutConfig) {
cfg.Observer = observer
}
}
|
