ceremonyclient/go-libp2p/p2p/host/eventbus/basic.go

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2023-08-21 03:50:38 +00:00
package eventbus
import (
"errors"
"fmt"
"reflect"
"sync"
"sync/atomic"
"github.com/libp2p/go-libp2p/core/event"
)
// /////////////////////
// BUS
// basicBus is a type-based event delivery system
type basicBus struct {
lk sync.RWMutex
nodes map[reflect.Type]*node
wildcard *wildcardNode
metricsTracer MetricsTracer
}
var _ event.Bus = (*basicBus)(nil)
type emitter struct {
n *node
w *wildcardNode
typ reflect.Type
closed atomic.Bool
dropper func(reflect.Type)
metricsTracer MetricsTracer
}
func (e *emitter) Emit(evt interface{}) error {
if e.closed.Load() {
return fmt.Errorf("emitter is closed")
}
e.n.emit(evt)
e.w.emit(evt)
if e.metricsTracer != nil {
e.metricsTracer.EventEmitted(e.typ)
}
return nil
}
func (e *emitter) Close() error {
if !e.closed.CompareAndSwap(false, true) {
return fmt.Errorf("closed an emitter more than once")
}
if e.n.nEmitters.Add(-1) == 0 {
e.dropper(e.typ)
}
return nil
}
func NewBus(opts ...Option) event.Bus {
bus := &basicBus{
nodes: map[reflect.Type]*node{},
wildcard: &wildcardNode{},
}
for _, opt := range opts {
opt(bus)
}
return bus
}
func (b *basicBus) withNode(typ reflect.Type, cb func(*node), async func(*node)) {
b.lk.Lock()
n, ok := b.nodes[typ]
if !ok {
n = newNode(typ, b.metricsTracer)
b.nodes[typ] = n
}
n.lk.Lock()
b.lk.Unlock()
cb(n)
if async == nil {
n.lk.Unlock()
} else {
go func() {
defer n.lk.Unlock()
async(n)
}()
}
}
func (b *basicBus) tryDropNode(typ reflect.Type) {
b.lk.Lock()
n, ok := b.nodes[typ]
if !ok { // already dropped
b.lk.Unlock()
return
}
n.lk.Lock()
if n.nEmitters.Load() > 0 || len(n.sinks) > 0 {
n.lk.Unlock()
b.lk.Unlock()
return // still in use
}
n.lk.Unlock()
delete(b.nodes, typ)
b.lk.Unlock()
}
type wildcardSub struct {
ch chan interface{}
w *wildcardNode
metricsTracer MetricsTracer
name string
}
func (w *wildcardSub) Out() <-chan interface{} {
return w.ch
}
func (w *wildcardSub) Close() error {
w.w.removeSink(w.ch)
if w.metricsTracer != nil {
w.metricsTracer.RemoveSubscriber(reflect.TypeOf(event.WildcardSubscription))
}
return nil
}
func (w *wildcardSub) Name() string {
return w.name
}
type namedSink struct {
name string
ch chan interface{}
}
type sub struct {
ch chan interface{}
nodes []*node
dropper func(reflect.Type)
metricsTracer MetricsTracer
name string
}
func (s *sub) Name() string {
return s.name
}
func (s *sub) Out() <-chan interface{} {
return s.ch
}
func (s *sub) Close() error {
go func() {
// drain the event channel, will return when closed and drained.
// this is necessary to unblock publishes to this channel.
for range s.ch {
}
}()
for _, n := range s.nodes {
n.lk.Lock()
for i := 0; i < len(n.sinks); i++ {
if n.sinks[i].ch == s.ch {
n.sinks[i], n.sinks[len(n.sinks)-1] = n.sinks[len(n.sinks)-1], nil
n.sinks = n.sinks[:len(n.sinks)-1]
if s.metricsTracer != nil {
s.metricsTracer.RemoveSubscriber(n.typ)
}
break
}
}
tryDrop := len(n.sinks) == 0 && n.nEmitters.Load() == 0
n.lk.Unlock()
if tryDrop {
s.dropper(n.typ)
}
}
close(s.ch)
return nil
}
var _ event.Subscription = (*sub)(nil)
// Subscribe creates new subscription. Failing to drain the channel will cause
// publishers to get blocked. CancelFunc is guaranteed to return after last send
// to the channel
func (b *basicBus) Subscribe(evtTypes interface{}, opts ...event.SubscriptionOpt) (_ event.Subscription, err error) {
settings := newSubSettings()
for _, opt := range opts {
if err := opt(&settings); err != nil {
return nil, err
}
}
if evtTypes == event.WildcardSubscription {
out := &wildcardSub{
ch: make(chan interface{}, settings.buffer),
w: b.wildcard,
metricsTracer: b.metricsTracer,
name: settings.name,
}
b.wildcard.addSink(&namedSink{ch: out.ch, name: out.name})
return out, nil
}
types, ok := evtTypes.([]interface{})
if !ok {
types = []interface{}{evtTypes}
}
if len(types) > 1 {
for _, t := range types {
if t == event.WildcardSubscription {
return nil, fmt.Errorf("wildcard subscriptions must be started separately")
}
}
}
out := &sub{
ch: make(chan interface{}, settings.buffer),
nodes: make([]*node, len(types)),
dropper: b.tryDropNode,
metricsTracer: b.metricsTracer,
name: settings.name,
}
for _, etyp := range types {
if reflect.TypeOf(etyp).Kind() != reflect.Ptr {
return nil, errors.New("subscribe called with non-pointer type")
}
}
for i, etyp := range types {
typ := reflect.TypeOf(etyp)
b.withNode(typ.Elem(), func(n *node) {
n.sinks = append(n.sinks, &namedSink{ch: out.ch, name: out.name})
out.nodes[i] = n
if b.metricsTracer != nil {
b.metricsTracer.AddSubscriber(typ.Elem())
}
}, func(n *node) {
if n.keepLast {
l := n.last
if l == nil {
return
}
out.ch <- l
}
})
}
return out, nil
}
// Emitter creates new emitter
//
// eventType accepts typed nil pointers, and uses the type information to
// select output type
//
// Example:
// emit, err := eventbus.Emitter(new(EventT))
// defer emit.Close() // MUST call this after being done with the emitter
//
// emit(EventT{})
func (b *basicBus) Emitter(evtType interface{}, opts ...event.EmitterOpt) (e event.Emitter, err error) {
if evtType == event.WildcardSubscription {
return nil, fmt.Errorf("illegal emitter for wildcard subscription")
}
var settings emitterSettings
for _, opt := range opts {
if err := opt(&settings); err != nil {
return nil, err
}
}
typ := reflect.TypeOf(evtType)
if typ.Kind() != reflect.Ptr {
return nil, errors.New("emitter called with non-pointer type")
}
typ = typ.Elem()
b.withNode(typ, func(n *node) {
n.nEmitters.Add(1)
n.keepLast = n.keepLast || settings.makeStateful
e = &emitter{n: n, typ: typ, dropper: b.tryDropNode, w: b.wildcard, metricsTracer: b.metricsTracer}
}, nil)
return
}
// GetAllEventTypes returns all the event types that this bus has emitters
// or subscribers for.
func (b *basicBus) GetAllEventTypes() []reflect.Type {
b.lk.RLock()
defer b.lk.RUnlock()
types := make([]reflect.Type, 0, len(b.nodes))
for t := range b.nodes {
types = append(types, t)
}
return types
}
// /////////////////////
// NODE
type wildcardNode struct {
sync.RWMutex
nSinks atomic.Int32
sinks []*namedSink
metricsTracer MetricsTracer
}
func (n *wildcardNode) addSink(sink *namedSink) {
n.nSinks.Add(1) // ok to do outside the lock
n.Lock()
n.sinks = append(n.sinks, sink)
n.Unlock()
if n.metricsTracer != nil {
n.metricsTracer.AddSubscriber(reflect.TypeOf(event.WildcardSubscription))
}
}
func (n *wildcardNode) removeSink(ch chan interface{}) {
n.nSinks.Add(-1) // ok to do outside the lock
n.Lock()
for i := 0; i < len(n.sinks); i++ {
if n.sinks[i].ch == ch {
n.sinks[i], n.sinks[len(n.sinks)-1] = n.sinks[len(n.sinks)-1], nil
n.sinks = n.sinks[:len(n.sinks)-1]
break
}
}
n.Unlock()
}
func (n *wildcardNode) emit(evt interface{}) {
if n.nSinks.Load() == 0 {
return
}
n.RLock()
for _, sink := range n.sinks {
// Sending metrics before sending on channel allows us to
// record channel full events before blocking
sendSubscriberMetrics(n.metricsTracer, sink)
sink.ch <- evt
}
n.RUnlock()
}
type node struct {
// Note: make sure to NEVER lock basicBus.lk when this lock is held
lk sync.Mutex
typ reflect.Type
// emitter ref count
nEmitters atomic.Int32
keepLast bool
last interface{}
sinks []*namedSink
metricsTracer MetricsTracer
}
func newNode(typ reflect.Type, metricsTracer MetricsTracer) *node {
return &node{
typ: typ,
metricsTracer: metricsTracer,
}
}
func (n *node) emit(evt interface{}) {
typ := reflect.TypeOf(evt)
if typ != n.typ {
panic(fmt.Sprintf("Emit called with wrong type. expected: %s, got: %s", n.typ, typ))
}
n.lk.Lock()
if n.keepLast {
n.last = evt
}
for _, sink := range n.sinks {
// Sending metrics before sending on channel allows us to
// record channel full events before blocking
sendSubscriberMetrics(n.metricsTracer, sink)
sink.ch <- evt
}
n.lk.Unlock()
}
func sendSubscriberMetrics(metricsTracer MetricsTracer, sink *namedSink) {
if metricsTracer != nil {
metricsTracer.SubscriberQueueLength(sink.name, len(sink.ch)+1)
metricsTracer.SubscriberQueueFull(sink.name, len(sink.ch)+1 >= cap(sink.ch))
metricsTracer.SubscriberEventQueued(sink.name)
}
}