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goevent.go
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/
goevent.go
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/*
Package goevent is event dispatcher.
Listen for event:
e := goevent.New()
e.On(func(i int, s string){
fmt.Printf("%d: %s\n", i, s)
})
Trigger:
e.Trigger(1, "foo")
Use event table:
table := goevent.NewTable()
table.On("foo", func(i int){
fmt.Printf("foo: %d\n", i)
})
table.On("bar", func(s string){
fmt.Printf("bar: %s\n", s)
})
table.Trigger("foo", 1)
table.Trigger("bar", "hoge")
table.Trigger("bar", 38) // retrun error
*/
package goevent
import (
"fmt"
"reflect"
"sync"
)
// Event is an event.
type Event interface {
Trigger(args ...interface{}) error
// f is a function
On(f interface{}) error
Off(f interface{}) error
}
type event struct {
// listeners are listener functions.
listeners []reflect.Value
lmu sync.RWMutex
argTypes []reflect.Type
tmu sync.RWMutex
}
// New creates a new event.
func New() Event {
return &event{}
}
var _ Event = New()
func (p *event) Trigger(args ...interface{}) error {
arguments := make([]reflect.Value, 0, len(args))
argTypes := make([]reflect.Type, 0, len(args))
for _, v := range args {
arguments = append(arguments, reflect.ValueOf(v))
argTypes = append(argTypes, reflect.TypeOf(v))
}
err := p.validateArgs(argTypes)
if err != nil {
return err
}
p.lmu.RLock()
defer p.lmu.RUnlock()
wg := sync.WaitGroup{}
wg.Add(len(p.listeners))
for _, fn := range p.listeners {
go func(f reflect.Value) {
defer wg.Done()
f.Call(arguments)
}(fn)
}
wg.Wait()
return nil
}
// Start to listen an event.
func (p *event) On(f interface{}) error {
fn, err := p.checkFuncSignature(f)
if err != nil {
return err
}
p.lmu.Lock()
defer p.lmu.Unlock()
p.listeners = append(p.listeners, *fn)
return nil
}
// Stop listening an event.
func (p *event) Off(f interface{}) error {
fn := reflect.ValueOf(f)
p.lmu.Lock()
defer p.lmu.Unlock()
l := len(p.listeners)
m := l // for error check
for i := 0; i < l; i++ {
if fn == p.listeners[i] {
// XXX: GC Ref: http://jxck.hatenablog.com/entry/golang-slice-internals
p.listeners = append(p.listeners[:i], p.listeners[i+1:]...)
l--
i--
}
}
if l == m {
return fmt.Errorf("Listener does't exists")
}
return nil
}
// retrun function as reflect.Value
// retrun error if f isn't function, argument is invalid
func (p *event) checkFuncSignature(f interface{}) (*reflect.Value, error) {
fn := reflect.ValueOf(f)
if fn.Kind() != reflect.Func {
return nil, fmt.Errorf("Argument should be a function")
}
types := fnArgTypes(fn)
p.lmu.RLock()
defer p.lmu.RUnlock()
if len(p.listeners) == 0 {
p.tmu.Lock()
defer p.tmu.Unlock()
p.argTypes = types
return &fn, nil
}
err := p.validateArgs(types)
if err != nil {
return nil, err
}
return &fn, nil
}
// if argument size or type are different return error.
func (p *event) validateArgs(types []reflect.Type) error {
p.tmu.RLock()
defer p.tmu.RUnlock()
if len(types) != len(p.argTypes) {
return fmt.Errorf("Argument length expected %d, but got %d", len(p.argTypes), len(types))
}
for i, t := range types {
if t != p.argTypes[i] {
return fmt.Errorf("Argument Error. Args[%d] expected %s, but got %s", i, p.argTypes[i], t)
}
}
return nil
}
// return argument types.
func fnArgTypes(fn reflect.Value) []reflect.Type {
fnType := fn.Type()
fnNum := fnType.NumIn()
types := make([]reflect.Type, 0, fnNum)
for i := 0; i < fnNum; i++ {
types = append(types, fnType.In(i))
}
return types
}