fix race problem

box.go

@@ -24,6 +24,15 @@ func NewCube(pos, size Vec3) (b *Cube) {
 	}
 }
 
+func NewCubeFromCenter(size Vec3) (b *Cube) {
+	pos := size
+	pos.ScaleN(-0.5)
+	return &Cube{
+		P: pos,
+		S: size,
+	}
+}
+
 func (b *Cube) String() string {
 	return "Cube(pos=" + b.P.String() + ", size=" + b.S.String() + ")"
 }

engine.go

@@ -98,6 +98,15 @@ func (e *Engine) GetObject(id uuid.UUID) *Object {
 	return e.objects[id]
 }
 
+func (e *Engine) ForeachObject(cb func(o *Object)) {
+	e.RLock()
+	defer e.RUnlock()
+
+	for _, o := range e.objects {
+		cb(o)
+	}
+}
+
 func (e *Engine) Events() []eventWave {
 	return e.events
 }
@@ -128,15 +137,18 @@ func (e *Engine) tickLocked(wg *sync.WaitGroup, dt float64) {
 	e.RLock()
 	defer e.RUnlock()
 
-	wg.Add(len(e.objects))
 	for _, o := range e.objects {
-		go func(o *Object) {
-			defer wg.Done()
-			o.tick(dt)
-		}(o)
+		if o.IsReady() {
+			wg.Add(1)
+			go func(o *Object) {
+				defer wg.Done()
+				o.tick(dt)
+			}(o)
+		}
 	}
 	for _, event := range e.events {
 		if event.Heavy() {
+			wg.Add(1)
 			go func(event eventWave) {
 				defer wg.Done()
 				event.Tick(dt, e)
@@ -151,12 +163,14 @@ func (e *Engine) saveStatusLocked(wg *sync.WaitGroup) {
 	e.Lock()
 	defer e.Unlock()
 
-	wg.Add(len(e.objects))
 	for _, o := range e.objects {
-		go func(o *Object) {
-			defer wg.Done()
-			o.saveStatus()
-		}(o)
+		if o.IsReady() {
+			wg.Add(1)
+			go func(o *Object) {
+				defer wg.Done()
+				o.saveStatus()
+			}(o)
+		}
 	}
 	for i := 0; i < len(e.events); {
 		event := e.events[i]

event.go

@@ -156,7 +156,7 @@ func (e *Engine) newGravityWave(sender *Object, center Vec3, f *GravityField, ti
 	g.f = *f
 	g.pos = center
 	g.gone = false
-	g.c = 1
+	g.c.Store(1)
 	maxRadius := -1.0
 	if e.cfg.MinAccel > 0 {
 		maxRadius = math.Sqrt(G / e.cfg.MinAccel * f.Mass())
@@ -181,7 +181,7 @@ func (e *Engine) newGravityWave(sender *Object, center Vec3, f *GravityField, ti
 		}
 		g.count()
 		r.passedGravity[sender] = g
-	}, false)
+	}, true)
 	w.onRemove = g.release
 	w.onBeforeTick = func(e *eventWaveFn) bool {
 		switch {

force.go

@@ -3,6 +3,7 @@ package molecular
 import (
 	"math"
 	"sync"
+	"sync/atomic"
 )
 
 const (
@@ -61,7 +62,7 @@ type gravityStatus struct {
 	pos Vec3
 
 	gone bool
-	c    int
+	c    atomic.Int32
 }
 
 var gravityStatusPool = sync.Pool{
@@ -76,21 +77,23 @@ func (s *gravityStatus) FieldAt(pos Vec3) Vec3 {
 
 func (s *gravityStatus) clone() (g *gravityStatus) {
 	g = gravityStatusPool.Get().(*gravityStatus)
-	*g = *s
-	g.c = 1
+	g.f = s.f
+	g.pos = s.pos
+	g.gone = false
+	g.c.Store(1)
 	return
 }
 
 func (s *gravityStatus) count() {
-	s.c++
+	s.c.Add(1)
 }
 
 func (s *gravityStatus) release() {
-	s.c--
-	if s.c < 0 {
+	c := s.c.Add(-1)
+	if c < 0 {
 		panic("gravityStatus.count become less than one")
 	}
-	if s.c == 0 {
+	if c == 0 {
 		gravityStatusPool.Put(s)
 	}
 }

object.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"math"
 	"sync"
+	"sync/atomic"
 
 	"github.com/google/uuid"
 )
@@ -57,8 +58,10 @@ func (s *objStatus) from(a *objStatus) {
 	for k, v := range a.passedGravity {
 		g := s.passedGravity[k]
 		if g != nil {
-			*g = *v
-			g.c = 1
+			g.f = v.f
+			g.pos = v.pos
+			g.gone = false
+			g.c.Store(1)
 		} else {
 			s.passedGravity[k] = v.clone()
 		}
@@ -97,13 +100,14 @@ func (s *objStatus) clone() (a objStatus) {
 // Object represents an object in the physics engine.
 type Object struct {
 	sync.RWMutex
+	ready  atomic.Bool
 	e      *Engine
 	id     uuid.UUID // a v7 UUID
 	typ    ObjType
 	blocks []Block
 	objStatus
 
-	// lastStatus should only be read during a tick
+	lastMux    sync.RWMutex
 	lastStatus objStatus
 
 	gtick uint16
@@ -148,6 +152,16 @@ func (o *Object) Engine() *Engine {
 	return o.e
 }
 
+// IsReady returns true when the object is ready to tick
+func (o *Object) IsReady() bool {
+	return o.ready.Load()
+}
+
+// Ready makes the IsReady returns true
+func (o *Object) Ready() {
+	o.ready.Store(true)
+}
+
 // Anchor returns this object's anchor object
 // If Anchor returns nil, the object is the main anchor
 func (o *Object) Anchor() *Object {
@@ -191,6 +205,9 @@ func (o *Object) SetHeadingVel(v Vec3) {
 // The new position will be calculated at the same time.
 // AttachTo must be called inside the object's tick
 func (o *Object) AttachTo(anchor *Object) {
+	o.lastMux.RLock()
+	defer o.lastMux.RUnlock()
+
 	if anchor == nil {
 		panic("molecular.Object: new anchor cannot be nil")
 	}
@@ -220,7 +237,6 @@ func (o *Object) AttachTo(anchor *Object) {
 			ScaleN(o.e.ReLorentzFactorSq(a.lastStatus.velocity.SqLen())).
 			Add(a.lastStatus.velocity)
 	})
-	hneg := o.lastStatus.heading.Negated()
 	v.Sub(v2)
 	o.anchor = anchor
 	o.pos = p
@@ -232,12 +248,20 @@ func (o *Object) forEachAnchor(cb func(*Object)) {
 	if o.lastStatus.anchor == nil {
 		return
 	}
-	cb(o.lastStatus.anchor)
-	o.lastStatus.anchor.forEachAnchor(cb)
+	a := o.lastStatus.anchor
+
+	a.lastMux.RLock()
+	defer a.lastMux.RUnlock()
+
+	cb(a)
+	a.forEachAnchor(cb)
 }
 
 // AbsPos returns the position relative to the main anchor
 func (o *Object) AbsPos() (p Vec3) {
+	o.lastMux.RLock()
+	defer o.lastMux.RUnlock()
+
 	p = o.lastStatus.pos
 	o.forEachAnchor(func(a *Object) {
 		p.Add(a.lastStatus.pos)
@@ -246,6 +270,9 @@ func (o *Object) AbsPos() (p Vec3) {
 }
 
 func (o *Object) RotatePos(p *Vec3) *Vec3 {
+	o.lastMux.RLock()
+	defer o.lastMux.RUnlock()
+
 	if o.anchor != nil {
 		p.
 			Sub(o.lastStatus.gcenter).
@@ -264,6 +291,9 @@ func (o *Object) SetVelocity(velocity Vec3) {
 }
 
 func (o *Object) AbsVelocity() (v Vec3) {
+	o.lastMux.RLock()
+	defer o.lastMux.RUnlock()
+
 	v = o.lastStatus.velocity
 	o.forEachAnchor(func(a *Object) {
 		v.
@@ -424,6 +454,8 @@ func (o *Object) tick(dt float64) {
 func (o *Object) saveStatus() {
 	o.RLock()
 	defer o.RUnlock()
+	o.lastMux.Lock()
+	defer o.lastMux.Unlock()
 
 	o.lastStatus.from(&o.objStatus)
 }