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parallel.go
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parallel.go
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package grouper
import (
"os"
"reflect"
"github.com/tedsuo/ifrit"
)
/*
NewParallel starts it's members simultaneously. Use a parallel group to describe a set
of concurrent but independent processes.
*/
func NewParallel(terminationSignal os.Signal, members Members) ifrit.Runner {
return parallelGroup{
terminationSignal: terminationSignal,
pool: make(map[string]ifrit.Process),
members: members,
}
}
type parallelGroup struct {
terminationSignal os.Signal
pool map[string]ifrit.Process
members Members
}
func (g parallelGroup) Run(signals <-chan os.Signal, ready chan<- struct{}) error {
err := g.validate()
if err != nil {
return err
}
signal, errTrace := g.parallelStart(signals)
if errTrace != nil {
return g.stop(g.terminationSignal, signals, errTrace).ErrorOrNil()
}
if signal != nil {
return g.stop(signal, signals, errTrace).ErrorOrNil()
}
close(ready)
signal, errTrace = g.waitForSignal(signals, errTrace)
return g.stop(signal, signals, errTrace).ErrorOrNil()
}
func (o parallelGroup) validate() error {
return o.members.Validate()
}
func (g *parallelGroup) parallelStart(signals <-chan os.Signal) (os.Signal, ErrorTrace) {
numMembers := len(g.members)
cases := make([]reflect.SelectCase, 2*numMembers+1)
for i, member := range g.members {
process := ifrit.Background(member)
g.pool[member.Name] = process
cases[2*i] = reflect.SelectCase{
Dir: reflect.SelectRecv,
Chan: reflect.ValueOf(process.Wait()),
}
cases[2*i+1] = reflect.SelectCase{
Dir: reflect.SelectRecv,
Chan: reflect.ValueOf(process.Ready()),
}
}
cases[2*numMembers] = reflect.SelectCase{
Dir: reflect.SelectRecv,
Chan: reflect.ValueOf(signals),
}
numReady := 0
for {
chosen, recv, _ := reflect.Select(cases)
switch {
case chosen == 2*numMembers:
return recv.Interface().(os.Signal), nil
case chosen%2 == 0:
recvError, _ := recv.Interface().(error)
return nil, ErrorTrace{ExitEvent{Member: g.members[chosen/2], Err: recvError}}
default:
cases[chosen].Chan = reflect.Zero(cases[chosen].Chan.Type())
numReady++
if numReady == numMembers {
return nil, nil
}
}
}
}
func (g *parallelGroup) 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 *parallelGroup) stop(signal os.Signal, signals <-chan os.Signal, errTrace ErrorTrace) ErrorTrace {
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
}
}
}
cases := make([]reflect.SelectCase, 0, len(g.members))
liveMembers := make([]Member, 0, len(g.members))
for _, member := range g.members {
if _, found := exited[member.Name]; found {
continue
}
process := g.pool[member.Name]
process.Signal(signal)
cases = append(cases, reflect.SelectCase{
Dir: reflect.SelectRecv,
Chan: reflect.ValueOf(process.Wait()),
})
liveMembers = append(liveMembers, member)
}
cases = append(cases, reflect.SelectCase{
Dir: reflect.SelectRecv,
Chan: reflect.ValueOf(signals),
})
// account for the signals channel
for numExited := 1; numExited < len(cases); numExited++ {
chosen, recv, _ := reflect.Select(cases)
cases[chosen].Chan = reflect.Zero(cases[chosen].Chan.Type())
recvError, _ := recv.Interface().(error)
if chosen == len(cases)-1 {
signal = recv.Interface().(os.Signal)
for _, member := range liveMembers {
g.pool[member.Name].Signal(signal)
}
continue
}
errTrace = append(errTrace, ExitEvent{
Member: liveMembers[chosen],
Err: recvError,
})
if recvError != nil {
errOccurred = true
}
}
if errOccurred {
return errTrace
}
return nil
}