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Duplicate response issues #184

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d6c3d4b
reproduce actor blocking on duplicate Respond call
mapogolions Feb 2, 2025
1c7caf3
reproduce receiving accidentally sent second result
mapogolions Feb 2, 2025
47b938c
fix issues caused by duplicate response
mapogolions Feb 2, 2025
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65 changes: 65 additions & 0 deletions actor/engine_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -480,3 +480,68 @@ func TestMultipleStops(t *testing.T) {
<-done
}
}

func TestShouldNotBlockActorOnAccidentalDuplicateRespond(t *testing.T) {
e, err := NewEngine(NewEngineConfig())
require.NoError(t, err)
pid := e.SpawnFunc(func(ctx *Context) {
msg := ctx.Message()
if s, ok := msg.(string); ok {
if s == "foo" {
ctx.Respond(len(s))
// missing `return` statement, causing an unintended second response
}
ctx.Respond(len(s)) // sends a duplicate response
}
}, "str", WithID("len"))

_ = e.Request(pid, "foo", 2*time.Second) // response will be consumed later
resp := e.Request(pid, "barbaz", 2*time.Second)

r, err := resp.Result()
require.NoError(t, err)
require.Equal(t, 6, r)
}

func TestShouldNotReceiveAccidentallySentSecondResult(t *testing.T) {
e, err := NewEngine(NewEngineConfig())
require.NoError(t, err)
done := make(chan struct{})
pid := e.SpawnFunc(func(ctx *Context) {
msg := ctx.Message()
if s, ok := msg.(string); ok && s == "foo" {
defer close(done)
if s == "foo" {
ctx.Respond(1)
// missing `return` statement, causing an unintended second response
}
select { // sends a duplicate response
case <-time.After(100 * time.Millisecond):
case <-runAsync(func() {
ctx.Respond(2)
}):
}
}
}, "kind")

resp := e.Request(pid, "foo", 200*time.Millisecond)
<-done

r, err := resp.Result()
require.NoError(t, err)
require.Equal(t, 1, r)
require.Nil(t, e.Registry.get(resp.pid))

r, err = resp.Result()
require.Error(t, err)
require.Nil(t, r)
}

func runAsync(f func()) <-chan struct{} {
ch := make(chan struct{})
go func() {
defer close(ch)
f()
}()
return ch
}
10 changes: 10 additions & 0 deletions actor/registry.go
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Original file line number Diff line number Diff line change
Expand Up @@ -69,3 +69,13 @@ func (r *Registry) add(proc Processer) {
r.mu.Unlock()
proc.Start()
}

func (r *Registry) remove(pid *PID) bool {
r.mu.Lock()
defer r.mu.Unlock()
_, ok := r.lookup[pid.ID]
if ok {
delete(r.lookup, pid.ID)
}
return ok
}
6 changes: 5 additions & 1 deletion actor/response.go
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,11 @@ func (r *Response) Result() (any, error) {
}

func (r *Response) Send(_ *PID, msg any, _ *PID) {
r.result <- msg
// Under normal conditions, the method is expected to be called only once.
// To prevent accidental duplicate responses, we promptly remove the process from the registry
if r.engine.Registry.remove(r.pid) {
r.result <- msg
}
}

func (r *Response) PID() *PID { return r.pid }
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