From b0e8700b6692d5cda275332482c2ca121902db5a Mon Sep 17 00:00:00 2001
From: Martin Geiseler <m.geiseler@global-communication.de>
Date: Thu, 4 Jul 2024 13:14:25 +0200
Subject: [PATCH 1/2] Fix poison deadlocking on non-existing pids

---
 actor/engine.go      | 19 ++++++++-----------
 actor/engine_test.go | 16 ++++++++++++++--
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/actor/engine.go b/actor/engine.go
index 8c785d8..ef9aa33 100644
--- a/actor/engine.go
+++ b/actor/engine.go
@@ -225,24 +225,21 @@ func (e *Engine) sendPoisonPill(pid *PID, graceful bool, wg ...*sync.WaitGroup)
 	} else {
 		_wg = &sync.WaitGroup{}
 	}
-	_wg.Add(1)
-	proc := e.Registry.get(pid)
+	pill := poisonPill{
+		wg:       _wg,
+		graceful: graceful,
+	}
 	// deadletter - if we didn't find a process, we will broadcast a DeadletterEvent
-	if proc == nil {
+	if e.Registry.get(pid) == nil {
 		e.BroadcastEvent(DeadLetterEvent{
 			Target:  pid,
-			Message: poisonPill{_wg, graceful},
+			Message: pill,
 			Sender:  nil,
 		})
 		return _wg
 	}
-	pill := poisonPill{
-		wg:       _wg,
-		graceful: graceful,
-	}
-	if proc != nil {
-		e.SendLocal(pid, pill, nil)
-	}
+	_wg.Add(1)
+	e.SendLocal(pid, pill, nil)
 	return _wg
 }
 
diff --git a/actor/engine_test.go b/actor/engine_test.go
index c2f3612..7f6d83f 100644
--- a/actor/engine_test.go
+++ b/actor/engine_test.go
@@ -284,7 +284,7 @@ func TestStop(t *testing.T) {
 
 func TestPoisonWaitGroup(t *testing.T) {
 	var (
-		wg = sync.WaitGroup{}
+		wg = &sync.WaitGroup{}
 		x  = int32(0)
 	)
 	e, err := NewEngine(NewEngineConfig())
@@ -303,6 +303,19 @@ func TestPoisonWaitGroup(t *testing.T) {
 
 	e.Poison(pid).Wait()
 	assert.Equal(t, int32(1), atomic.LoadInt32(&x))
+
+	// validate poisoning non exiting pid does not deadlock
+	wg = e.Poison(NewPID(LocalLookupAddr, "non-existing"))
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		wg.Wait()
+	}()
+	select {
+	case <-done:
+	case <-time.After(20 * time.Millisecond):
+		t.Error("poison waitGroup deadlocked")
+	}
 }
 
 func TestPoison(t *testing.T) {
@@ -327,7 +340,6 @@ func TestPoison(t *testing.T) {
 		// When a process is poisoned it should be removed from the registry.
 		// Hence, we should get NIL when we try to get it.
 		assert.Nil(t, e.Registry.get(pid))
-
 	}
 }
 

From e1077eb5746254109b769b9d5f1283f6f64dd677 Mon Sep 17 00:00:00 2001
From: Martin Geiseler <m.geiseler@global-communication.de>
Date: Fri, 5 Jul 2024 09:34:36 +0200
Subject: [PATCH 2/2] Prevent nil pointer dereference

poisonDeadlock
---
 actor/engine_test.go | 2 ++
 actor/registry.go    | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/actor/engine_test.go b/actor/engine_test.go
index 7f6d83f..1201300 100644
--- a/actor/engine_test.go
+++ b/actor/engine_test.go
@@ -316,6 +316,8 @@ func TestPoisonWaitGroup(t *testing.T) {
 	case <-time.After(20 * time.Millisecond):
 		t.Error("poison waitGroup deadlocked")
 	}
+	// ... or panic
+	e.Poison(nil).Wait()
 }
 
 func TestPoison(t *testing.T) {
diff --git a/actor/registry.go b/actor/registry.go
index 0bf5869..be190ac 100644
--- a/actor/registry.go
+++ b/actor/registry.go
@@ -40,6 +40,9 @@ func (r *Registry) Remove(pid *PID) {
 // If it doesn't exist, nil is returned so the caller must check for that
 // and direct the message to the deadletter processer instead.
 func (r *Registry) get(pid *PID) Processer {
+	if pid == nil {
+		return nil
+	}
 	r.mu.RLock()
 	defer r.mu.RUnlock()
 	if proc, ok := r.lookup[pid.ID]; ok {