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package document
import (
"fmt"
"sync"
"sync/atomic"
"time"
)
const maxAttempts = 10
// Dispatcher dispatches documents from a queue to a Feeder.
type Dispatcher struct {
feeder Feeder
throttler Throttler
circuitBreaker CircuitBreaker
stats Stats
closed bool
ready chan Id
results chan Result
inflight map[string]*documentGroup
inflightCount int64
mu sync.RWMutex
wg sync.WaitGroup
resultWg sync.WaitGroup
}
// documentGroup holds document operations which share their ID, and must be dispatched in order.
type documentGroup struct {
id Id
operations []documentOp
mu sync.Mutex
}
type documentOp struct {
document Document
attempts int
}
func (g *documentGroup) append(op documentOp) {
g.mu.Lock()
defer g.mu.Unlock()
g.operations = append(g.operations, op)
}
func NewDispatcher(feeder Feeder, throttler Throttler, breaker CircuitBreaker) *Dispatcher {
d := &Dispatcher{
feeder: feeder,
throttler: throttler,
circuitBreaker: breaker,
inflight: make(map[string]*documentGroup),
}
d.start()
return d
}
func (d *Dispatcher) dispatchAll(g *documentGroup) {
g.mu.Lock()
defer g.mu.Unlock()
for i := 0; i < len(g.operations); i++ {
op := g.operations[i]
ok := false
for !ok {
op.attempts++
result := d.feeder.Send(op.document)
d.results <- result
ok = result.Status.Success()
if !d.shouldRetry(op, result) {
break
}
}
d.releaseSlot()
}
g.operations = nil
}
func (d *Dispatcher) shouldRetry(op documentOp, result Result) bool {
if result.HTTPStatus/100 == 2 || result.HTTPStatus == 404 || result.HTTPStatus == 412 {
d.throttler.Success()
d.circuitBreaker.Success()
return false
}
if result.HTTPStatus == 429 || result.HTTPStatus == 503 {
d.throttler.Throttled(atomic.LoadInt64(&d.inflightCount))
return true
}
if result.HTTPStatus == 500 || result.HTTPStatus == 502 || result.HTTPStatus == 504 {
d.circuitBreaker.Error(fmt.Errorf("request failed with status %d", result.HTTPStatus))
if op.attempts <= maxAttempts {
return true
}
}
return false
}
func (d *Dispatcher) start() {
d.mu.Lock()
defer d.mu.Unlock()
d.ready = make(chan Id, 4096)
d.results = make(chan Result, 4096)
d.closed = false
d.wg.Add(1)
go func() {
defer d.wg.Done()
d.readDocuments()
}()
d.resultWg.Add(1)
go func() {
defer d.resultWg.Done()
d.readResults()
}()
}
func (d *Dispatcher) readDocuments() {
for id := range d.ready {
d.mu.RLock()
group := d.inflight[id.String()]
d.mu.RUnlock()
if group != nil {
d.wg.Add(1)
go func() {
defer d.wg.Done()
d.dispatchAll(group)
}()
}
}
}
func (d *Dispatcher) readResults() {
for result := range d.results {
d.stats.Add(result.Stats)
}
}
func (d *Dispatcher) Enqueue(doc Document) error {
d.mu.Lock()
if d.closed {
return fmt.Errorf("dispatcher is closed")
}
group, ok := d.inflight[doc.Id.String()]
if ok {
group.append(documentOp{document: doc})
} else {
group = &documentGroup{
id: doc.Id,
operations: []documentOp{{document: doc}},
}
d.inflight[doc.Id.String()] = group
}
d.mu.Unlock()
d.enqueueWithSlot(doc.Id)
return nil
}
func (d *Dispatcher) Stats() Stats { return d.stats }
func (d *Dispatcher) enqueueWithSlot(id Id) {
d.acquireSlot()
d.ready <- id
d.throttler.Sent()
}
func (d *Dispatcher) acquireSlot() {
for atomic.LoadInt64(&d.inflightCount) >= d.throttler.TargetInflight() {
time.Sleep(time.Millisecond)
}
atomic.AddInt64(&d.inflightCount, 1)
}
func (d *Dispatcher) releaseSlot() { atomic.AddInt64(&d.inflightCount, -1) }
func closeAndWait[T any](ch chan T, wg *sync.WaitGroup, d *Dispatcher, markClosed bool) {
d.mu.Lock()
if !d.closed {
close(ch)
if markClosed {
d.closed = true
}
}
d.mu.Unlock()
wg.Wait()
}
// Close closes the dispatcher and waits for all inflight operations to complete.
func (d *Dispatcher) Close() error {
closeAndWait(d.ready, &d.wg, d, false)
closeAndWait(d.results, &d.resultWg, d, true)
return nil
}
|
