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ordered.go
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ordered.go
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package grouper
import (
"os"
"reflect"
"github.com/tedsuo/ifrit"
)
/*
NewOrdered starts it's members in order, each member starting when the previous
becomes ready. On shutdown, it will shut the started processes down in reverse order.
Use an ordered group to describe a list of dependent processes, where each process
depends upon the previous being available in order to function correctly.
*/
func NewOrdered(terminationSignal os.Signal, members Members) ifrit.Runner {
return &orderedGroup{
terminationSignal: terminationSignal,
pool: make(map[string]ifrit.Process),
members: members,
}
}
type orderedGroup struct {
terminationSignal os.Signal
pool map[string]ifrit.Process
members Members
}
func (g *orderedGroup) Run(signals <-chan os.Signal, ready chan<- struct{}) error {
err := g.validate()
if err != nil {
return err
}
signal, errTrace := g.orderedStart(signals)
if errTrace != nil {
return g.stop(g.terminationSignal, signals, errTrace)
}
if signal != nil {
return g.stop(signal, signals, errTrace)
}
close(ready)
signal, errTrace = g.waitForSignal(signals, errTrace)
return g.stop(signal, signals, errTrace)
}
func (g *orderedGroup) validate() error {
return g.members.Validate()
}
func (g *orderedGroup) orderedStart(signals <-chan os.Signal) (os.Signal, ErrorTrace) {
for _, member := range g.members {
p := ifrit.Background(member)
select {
case <-p.Ready():
g.pool[member.Name] = p
case err := <-p.Wait():
return nil, ErrorTrace{
ExitEvent{Member: member, Err: err},
}
case signal := <-signals:
return signal, nil
}
}
return nil, nil
}
func (g *orderedGroup) waitForSignal(signals <-chan os.Signal, errTrace ErrorTrace) (os.Signal, ErrorTrace) {
cases := make([]reflect.SelectCase, 0, len(g.pool)+1)
for i := 0; i < len(g.pool); i++ {
cases = append(cases, reflect.SelectCase{
Dir: reflect.SelectRecv,
Chan: reflect.ValueOf(g.pool[g.members[i].Name].Wait()),
})
}
cases = append(cases, reflect.SelectCase{
Dir: reflect.SelectRecv,
Chan: reflect.ValueOf(signals),
})
chosen, recv, _ := reflect.Select(cases)
if chosen == len(cases)-1 {
return recv.Interface().(os.Signal), errTrace
}
var err error
if !recv.IsNil() {
err = recv.Interface().(error)
}
errTrace = append(errTrace, ExitEvent{
Member: g.members[chosen],
Err: err,
})
return g.terminationSignal, errTrace
}
func (g *orderedGroup) stop(signal os.Signal, signals <-chan os.Signal, errTrace ErrorTrace) error {
errOccurred := false
exited := map[string]struct{}{}
if len(errTrace) > 0 {
for _, exitEvent := range errTrace {
exited[exitEvent.Member.Name] = struct{}{}
if exitEvent.Err != nil {
errOccurred = true
}
}
}
for i := len(g.pool) - 1; i >= 0; i-- {
m := g.members[i]
if _, found := exited[m.Name]; found {
continue
}
if p, ok := g.pool[m.Name]; ok {
p.Signal(signal)
select {
case err := <-p.Wait():
errTrace = append(errTrace, ExitEvent{
Member: m,
Err: err,
})
if err != nil {
errOccurred = true
}
case signal := <-signals:
p.Signal(signal)
}
}
}
if errOccurred {
return errTrace
}
return nil
}