From b2f0ab5cc1b0529718bd94b4b3770787847fe409 Mon Sep 17 00:00:00 2001
From: Igor Kuzmin <146714691+kuzmig@users.noreply.github.com>
Date: Tue, 13 Feb 2024 19:20:45 +0300
Subject: [PATCH] Deadlock calling Event in after-event callback when current
 state == dst (#104)

* Deadlock in afterEventCallbacks in case when src == dst fixed

* Test added

---------

Co-authored-by: Igor Kuzmin <i.kuzmin@webinar.ru>
---
 fsm.go      |  4 ++++
 fsm_test.go | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/fsm.go b/fsm.go
index bd269d7..4465867 100644
--- a/fsm.go
+++ b/fsm.go
@@ -333,6 +333,10 @@ func (f *FSM) Event(ctx context.Context, event string, args ...interface{}) erro
 	}
 
 	if f.current == dst {
+		f.stateMu.RUnlock()
+		defer f.stateMu.RLock()
+		f.eventMu.Unlock()
+		unlocked = true
 		f.afterEventCallbacks(ctx, e)
 		return NoTransitionError{e.Err}
 	}
diff --git a/fsm_test.go b/fsm_test.go
index 8e0c4ed..4d4479a 100644
--- a/fsm_test.go
+++ b/fsm_test.go
@@ -825,6 +825,31 @@ func TestNoTransition(t *testing.T) {
 	}
 }
 
+func TestNoTransitionAfterEventCallbackTransition(t *testing.T) {
+	var fsm *FSM
+	fsm = NewFSM(
+		"start",
+		Events{
+			{Name: "run", Src: []string{"start"}, Dst: "start"},
+			{Name: "finish", Src: []string{"start"}, Dst: "finished"},
+		},
+		Callbacks{
+			"after_event": func(_ context.Context, e *Event) {
+				fsm.Event(context.Background(), "finish")
+			},
+		},
+	)
+	err := fsm.Event(context.Background(), "run")
+	if _, ok := err.(NoTransitionError); !ok {
+		t.Error("expected 'NoTransitionError'")
+	}
+
+	currentState := fsm.Current()
+	if currentState != "finished" {
+		t.Errorf("expected state to be 'finished', was '%s'", currentState)
+	}
+}
+
 func ExampleNewFSM() {
 	fsm := NewFSM(
 		"green",