Use workerpools to enforce FIFO without blocking other topics

This commit is contained in:
Dane Everitt 2020-09-12 20:13:59 -07:00
parent 53bd0d57ad
commit d02e37620d
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GPG Key ID: EEA66103B3D71F53
3 changed files with 90 additions and 44 deletions

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@ -2,8 +2,9 @@ package events
import ( import (
"encoding/json" "encoding/json"
"fmt"
"github.com/gammazero/workerpool"
"github.com/pkg/errors" "github.com/pkg/errors"
"reflect"
"strings" "strings"
"sync" "sync"
) )
@ -14,13 +15,13 @@ type Event struct {
} }
type EventBus struct { type EventBus struct {
mu sync.RWMutex mu sync.RWMutex
callbacks map[string][]*func(Event) pools map[string]*CallbackPool
} }
func New() *EventBus { func New() *EventBus {
return &EventBus{ return &EventBus{
callbacks: make(map[string][]*func(Event)), pools: make(map[string]*CallbackPool),
} }
} }
@ -46,12 +47,25 @@ func (e *EventBus) Publish(topic string, data string) {
// Acquire a read lock and loop over all of the channels registered for the topic. This // Acquire a read lock and loop over all of the channels registered for the topic. This
// avoids a panic crash if the process tries to unregister the channel while this routine // avoids a panic crash if the process tries to unregister the channel while this routine
// is running. // is running.
if _, ok := e.callbacks[t]; ok { if cp, ok := e.pools[t]; ok {
evt := Event{Data: data, Topic: topic} evt := Event{Data: data, Topic: topic}
for _, callback := range e.callbacks[t] {
go func(evt Event, callback func(Event)) { for _, callback := range cp.callbacks {
callback(evt) c := *callback
}(evt, *callback) evt := evt
// Using the workerpool with one worker allows us to execute events in a FIFO manner. Running
// this using goroutines would cause things such as console output to just output in random order
// if more than one event is fired at the same time.
//
// However, the pool submission does not block the execution of this function itself, allowing
// us to call publish without blocking any of the other pathways.
//
// @see https://github.com/pterodactyl/panel/issues/2303
fmt.Println("pre-submit for topic:", evt.Topic)
cp.pool.Submit(func() {
fmt.Println("executing callback for event:", evt.Topic)
c(evt)
})
} }
} }
} }
@ -76,15 +90,17 @@ func (e *EventBus) On(topic string, callback *func(Event)) {
// Check if this topic has been registered at least once for the event listener, and if // Check if this topic has been registered at least once for the event listener, and if
// not create an empty struct for the topic. // not create an empty struct for the topic.
if _, exists := e.callbacks[topic]; !exists { if _, exists := e.pools[topic]; !exists {
e.callbacks[topic] = make([]*func(Event), 0) fmt.Println("no pool for topic, creating:", topic)
e.pools[topic] = &CallbackPool{
callbacks: make([]*func(Event), 0),
pool: workerpool.New(1),
}
} }
// If this callback is not already registered as an event listener, go ahead and append // If this callback is not already registered as an event listener, go ahead and append
// it to the array of callbacks for this topic. // it to the array of callbacks for this topic.
if e.index(topic, reflect.ValueOf(callback)) < 0 { e.pools[topic].Add(callback)
e.callbacks[topic] = append(e.callbacks[topic], callback)
}
} }
// Removes an event listener from the bus. // Removes an event listener from the bus.
@ -92,41 +108,22 @@ func (e *EventBus) Off(topic string, callback *func(Event)) {
e.mu.Lock() e.mu.Lock()
defer e.mu.Unlock() defer e.mu.Unlock()
i := e.index(topic, reflect.ValueOf(callback)) if cp, ok := e.pools[topic]; ok {
cp.Remove(callback)
// If i < 0 it means there was no index found for the given callback, meaning it was
// never registered or was already unregistered from the listeners. Also double check
// that we didn't somehow escape the length of the topic callback (not sure how that
// would happen, but lets avoid a panic condition).
if i < 0 || i >= len(e.callbacks[topic]) {
return
} }
// We can assume that the topic still exists at this point since we acquire an exclusive
// lock on the process, and the "e.index" function cannot return a value >= 0 if there is
// no topic already existing.
e.callbacks[topic] = append(e.callbacks[topic][:i], e.callbacks[topic][i+1:]...)
} }
// Removes all of the event listeners that have been registered for any topic. // Removes all of the event listeners that have been registered for any topic. Also stops the worker
func (e *EventBus) RemoveAll() { // pool to close that routine.
func (e *EventBus) Destroy() {
e.mu.Lock() e.mu.Lock()
defer e.mu.Unlock() defer e.mu.Unlock()
e.callbacks = make(map[string][]*func(Event)) fmt.Println("destroying pool for event bus")
} // Stop every pool that exists for a given callback topic.
for _, cp := range e.pools {
// Finds the index of a given callback in the topic by comparing all of the registered callback cp.pool.Stop()
// pointers to the passed function. This function does not aquire a lock as it should only be called
// within the confines of a function that has already acquired a lock for the duration of the lookup.
func (e *EventBus) index(topic string, v reflect.Value) int {
if _, ok := e.callbacks[topic]; ok {
for i, handler := range e.callbacks[topic] {
if reflect.ValueOf(handler).Pointer() == v.Pointer() {
return i
}
}
} }
return -1 e.pools = make(map[string]*CallbackPool)
} }

49
events/pool.go Normal file
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@ -0,0 +1,49 @@
package events
import (
"github.com/gammazero/workerpool"
"reflect"
)
type CallbackPool struct {
callbacks []*func(Event)
pool *workerpool.WorkerPool
}
// Pushes a new callback into the array of listeners for the pool.
func (cp *CallbackPool) Add(callback *func(Event)) {
if cp.index(reflect.ValueOf(callback)) < 0 {
cp.callbacks = append(cp.callbacks, callback)
}
}
// Removes a callback from the array of registered callbacks if it exists.
func (cp *CallbackPool) Remove(callback *func(Event)) {
i := cp.index(reflect.ValueOf(callback))
// If i < 0 it means there was no index found for the given callback, meaning it was
// never registered or was already unregistered from the listeners. Also double check
// that we didn't somehow escape the length of the topic callback (not sure how that
// would happen, but lets avoid a panic condition).
if i < 0 || i >= len(cp.callbacks) {
return
}
// We can assume that the topic still exists at this point since we acquire an exclusive
// lock on the process, and the "e.index" function cannot return a value >= 0 if there is
// no topic already existing.
cp.callbacks = append(cp.callbacks[:i], cp.callbacks[i+1:]...)
}
// Finds the index of a given callback in the topic by comparing all of the registered callback
// pointers to the passed function. This function does not aquire a lock as it should only be called
// within the confines of a function that has already acquired a lock for the duration of the lookup.
func (cp *CallbackPool) index(v reflect.Value) int {
for i, handler := range cp.callbacks {
if reflect.ValueOf(handler).Pointer() == v.Pointer() {
return i
}
}
return -1
}

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@ -198,7 +198,7 @@ func deleteServer(c *gin.Context) {
} }
// Unsubscribe all of the event listeners. // Unsubscribe all of the event listeners.
s.Events().RemoveAll() s.Events().Destroy()
// Destroy the environment; in Docker this will handle a running container and // Destroy the environment; in Docker this will handle a running container and
// forcibly terminate it before removing the container, so we do not need to handle // forcibly terminate it before removing the container, so we do not need to handle