implement halting as state machine

lotus-soup/compositions/composition-drand-halt.toml

@@ -68,6 +68,5 @@
     [groups.run.test_params]
       role = "drand"
       drand_period = "1s"
-      drand_halt_duration = "1m"
-      drand_halt_begin = "10s"
       drand_log_level = "none"
+      suspend_events = "wait 20s -> halt -> wait 45s -> resume -> wait 5s -> halt -> wait 1m -> resume"

lotus-soup/node.go

@@ -70,11 +70,10 @@ func (t *TestEnvironment) DurationParam(name string) time.Duration {
 	return d
 }
 
-func (t *TestEnvironment) DebugSpew(format string, args... interface{}) {
+func (t *TestEnvironment) DebugSpew(format string, args ...interface{}) {
 	t.RecordMessage(spew.Sprintf(format, args...))
 }
 
-
 type Node struct {
 	fullApi  api.FullNode
 	minerApi api.StorageMiner

lotus-soup/role_drand.go

@@ -24,6 +24,8 @@ import (
 	"github.com/libp2p/go-libp2p-core/peer"
 	ma "github.com/multiformats/go-multiaddr"
 	"github.com/testground/sdk-go/sync"
+
+	"github.com/filecoin-project/oni/lotus-soup/statemachine"
 )
 
 var (
@@ -121,14 +123,14 @@ func (dr *DrandInstance) RunDKG(nodes, thr int, timeout string, leader bool, lea
 	return kg
 }
 
-func (dr *DrandInstance) Halt(duration time.Duration) {
-	dr.t.RecordMessage("drand node %d halting for %s", dr.t.GroupSeq, duration.String())
+func (dr *DrandInstance) Halt() {
+	dr.t.RecordMessage("drand node #%d halting", dr.t.GroupSeq)
 	dr.daemon.StopBeacon()
+}
 
-	time.AfterFunc(duration, func() {
-		dr.t.RecordMessage("drand node %d coming back online", dr.t.GroupSeq)
+func (dr *DrandInstance) Resume() {
+	dr.t.RecordMessage("drand node #d resuming", dr.t.GroupSeq)
 	dr.daemon.StartBeacon(true)
-	})
 }
 
 func runDrandNode(t *TestEnvironment) error {
@@ -142,15 +144,9 @@ func runDrandNode(t *TestEnvironment) error {
 	ctx := context.Background()
 	t.SyncClient.MustSignalAndWait(ctx, stateReady, t.TestInstanceCount)
 
-	haltDuration := time.Duration(0)
-	if t.IsParamSet("drand_halt_duration") {
-		haltDuration = t.DurationParam("drand_halt_duration")
-	}
-	if haltDuration != 0 {
-		startTime := t.DurationParam("drand_halt_begin")
-		time.AfterFunc(startTime, func() {
-			dr.Halt(haltDuration)
-		})
+	if t.IsParamSet("suspend_events") {
+		suspender := statemachine.NewSuspender(dr, t.RecordMessage)
+		suspender.RunEvents(t.StringParam("suspend_events"))
 	}
 
 	t.SyncClient.MustSignalAndWait(ctx, stateDone, t.TestInstanceCount)

lotus-soup/statemachine/statemachine.go

@@ -0,0 +1,108 @@
+package statemachine
+
+import (
+	"errors"
+	"sync"
+)
+
+// This code has been shamelessly lifted from this blog post:
+// https://venilnoronha.io/a-simple-state-machine-framework-in-go
+// Many thanks to the author, Venil Norohnha
+
+// ErrEventRejected is the error returned when the state machine cannot process
+// an event in the state that it is in.
+var ErrEventRejected = errors.New("event rejected")
+
+const (
+	// Default represents the default state of the system.
+	Default StateType = ""
+
+	// NoOp represents a no-op event.
+	NoOp EventType = "NoOp"
+)
+
+// StateType represents an extensible state type in the state machine.
+type StateType string
+
+// EventType represents an extensible event type in the state machine.
+type EventType string
+
+// EventContext represents the context to be passed to the action implementation.
+type EventContext interface{}
+
+// Action represents the action to be executed in a given state.
+type Action interface {
+	Execute(eventCtx EventContext) EventType
+}
+
+// Events represents a mapping of events and states.
+type Events map[EventType]StateType
+
+// State binds a state with an action and a set of events it can handle.
+type State struct {
+	Action Action
+	Events Events
+}
+
+// States represents a mapping of states and their implementations.
+type States map[StateType]State
+
+// StateMachine represents the state machine.
+type StateMachine struct {
+	// Previous represents the previous state.
+	Previous StateType
+
+	// Current represents the current state.
+	Current StateType
+
+	// States holds the configuration of states and events handled by the state machine.
+	States States
+
+	// mutex ensures that only 1 event is processed by the state machine at any given time.
+	mutex sync.Mutex
+}
+
+// getNextState returns the next state for the event given the machine's current
+// state, or an error if the event can't be handled in the given state.
+func (s *StateMachine) getNextState(event EventType) (StateType, error) {
+	if state, ok := s.States[s.Current]; ok {
+		if state.Events != nil {
+			if next, ok := state.Events[event]; ok {
+				return next, nil
+			}
+		}
+	}
+	return Default, ErrEventRejected
+}
+
+// SendEvent sends an event to the state machine.
+func (s *StateMachine) SendEvent(event EventType, eventCtx EventContext) error {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
+	for {
+		// Determine the next state for the event given the machine's current state.
+		nextState, err := s.getNextState(event)
+		if err != nil {
+			return ErrEventRejected
+		}
+
+		// Identify the state definition for the next state.
+		state, ok := s.States[nextState]
+		if !ok || state.Action == nil {
+			// configuration error
+		}
+
+		// Transition over to the next state.
+		s.Previous = s.Current
+		s.Current = nextState
+
+		// Execute the next state's action and loop over again if the event returned
+		// is not a no-op.
+		nextEvent := state.Action.Execute(eventCtx)
+		if nextEvent == NoOp {
+			return nil
+		}
+		event = nextEvent
+	}
+}

lotus-soup/statemachine/suspend.go

@@ -0,0 +1,128 @@
+package statemachine
+
+import (
+	"fmt"
+	"strings"
+	"time"
+)
+
+const (
+	Running   StateType = "running"
+	Suspended StateType = "suspended"
+
+	Halt   EventType = "halt"
+	Resume EventType = "resume"
+)
+
+type Suspendable interface {
+	Halt()
+	Resume()
+}
+
+type HaltAction struct{}
+
+func (a *HaltAction) Execute(ctx EventContext) EventType {
+	s, ok := ctx.(*Suspender)
+	if !ok {
+		fmt.Println("unable to halt, event context is not Suspendable")
+		return NoOp
+	}
+	s.target.Halt()
+	return NoOp
+}
+
+type ResumeAction struct{}
+
+func (a *ResumeAction) Execute(ctx EventContext) EventType {
+	s, ok := ctx.(*Suspender)
+	if !ok {
+		fmt.Println("unable to resume, event context is not Suspendable")
+		return NoOp
+	}
+	s.target.Resume()
+	return NoOp
+}
+
+type Suspender struct {
+	StateMachine
+	target Suspendable
+	log    LogFn
+}
+
+type LogFn func(fmt string, args ...interface{})
+
+func NewSuspender(target Suspendable, log LogFn) *Suspender {
+	return &Suspender{
+		target: target,
+		log:    log,
+		StateMachine: StateMachine{
+			Current: Running,
+			States: States{
+				Running: State{
+					Action: &ResumeAction{},
+					Events: Events{
+						Halt: Suspended,
+					},
+				},
+
+				Suspended: State{
+					Action: &HaltAction{},
+					Events: Events{
+						Resume: Running,
+					},
+				},
+			},
+		},
+	}
+}
+
+func (s *Suspender) RunEvents(eventSpec string) {
+	s.log("running event spec: %s", eventSpec)
+	for _, et := range parseEventSpec(eventSpec, s.log) {
+		if et.delay != 0 {
+			//s.log("waiting %s", et.delay.String())
+			time.Sleep(et.delay)
+			continue
+		}
+		if et.event == "" {
+			s.log("ignoring empty event")
+			continue
+		}
+		s.log("sending event %s", et.event)
+		err := s.SendEvent(et.event, s)
+		if err != nil {
+			s.log("error sending event %s: %s", et.event, err)
+		}
+	}
+}
+
+type eventTiming struct {
+	delay time.Duration
+	event EventType
+}
+
+func parseEventSpec(spec string, log LogFn) []eventTiming {
+	fields := strings.Split(spec, "->")
+	out := make([]eventTiming, 0, len(fields))
+	for _, f := range fields {
+		f = strings.TrimSpace(f)
+		words := strings.Split(f, " ")
+
+		// TODO: try to implement a "waiting" state instead of special casing like this
+		if words[0] == "wait" {
+			if len(words) != 2 {
+				log("expected 'wait' to be followed by duration, e.g. 'wait 30s'. ignoring.")
+				continue
+			}
+			d, err := time.ParseDuration(words[1])
+			if err != nil {
+				log("bad argument for 'wait': %s", err)
+				continue
+			}
+			out = append(out, eventTiming{delay: d})
+		} else {
+			out = append(out, eventTiming{event: EventType(words[0])})
+		}
+	}
+	return out
+}