future.go

package raft

import (
	"net"
	"time"
)

// Future is used to represent an action that may occur in the future
type Future interface {
	Error() error
}

// ApplyFuture is used for Apply() and can returns the FSM response
type ApplyFuture interface {
	Future
	Response() interface{}
}

// errorFuture is used to return a static error
type errorFuture struct {
	err error
}

func (e errorFuture) Error() error {
	return e.err
}

func (e errorFuture) Response() interface{} {
	return nil
}

// deferError can be embedded to allow a future
// to provide an error in the future
type deferError struct {
	err   error
	errCh chan error
}

func (d *deferError) init() {
	d.errCh = make(chan error, 1)
}

func (d *deferError) Error() error {
	if d.err != nil {
		return d.err
	}
	if d.errCh == nil {
		panic("waiting from response on nil channel")
	}
	d.err = <-d.errCh
	return d.err
}

func (d *deferError) respond(err error) {
	if d.errCh == nil {
		return
	}
	d.errCh <- err
	close(d.errCh)
}

// logFuture is used to apply a log entry and waits until
// the log is considered committed
type logFuture struct {
	deferError
	log      Log
	policy   quorumPolicy
	response interface{}
}

func (l *logFuture) Response() interface{} {
	return l.response
}

type shutdownFuture struct {
	raft *Raft
}

func (s *shutdownFuture) Error() error {
	for s.raft.getRoutines() > 0 {
		time.Sleep(5 * time.Millisecond)
	}
	return nil
}

// snapshotFuture is used for waiting on a snapshot to complete
type snapshotFuture struct {
	deferError
}

// reqSnapshotFuture is used for requesting a snapshot start.
// It is only used internally
type reqSnapshotFuture struct {
	deferError

	// snapshot details provided by the FSM runner before responding
	index    uint64
	term     uint64
	peers    []net.Addr
	snapshot FSMSnapshot
}

// restoreFuture is used for requesting an FSM to perform a
// snapshot restore. Used internally only.
type restoreFuture struct {
	deferError
	ID string
}