ar: AllocState should not mutate ar.state

If ar.state.TaskStates has not been set, set it on the copy of ar.state.
That keeps ar.state manipulations in one location and allows AllocState
to only acquire read-locks.

client/allocrunnerv2/alloc_runner.go

@@ -56,7 +56,8 @@ type allocRunner struct {
 	alloc     *structs.Allocation
 	allocLock sync.RWMutex
 
-	state     *state.State // alloc runner state
+	// state is the alloc runner's state
+	state     *state.State
 	stateLock sync.RWMutex
 
 	stateDB cstate.StateDB
@@ -391,22 +392,22 @@ func getClientStatus(taskStates map[string]*structs.TaskState) (status, descript
 // AllocState returns a copy of allocation state including a snapshot of task
 // states.
 func (ar *allocRunner) AllocState() *state.State {
-	// Must acquire write-lock in case TaskStates needs to be set.
-	ar.stateLock.Lock()
-	defer ar.stateLock.Unlock()
+	ar.stateLock.RLock()
+	state := ar.state.Copy()
+	ar.stateLock.RUnlock()
 
 	// If TaskStateUpdated has not been called yet, ar.state.TaskStates
 	// won't be set as it is not the canonical source of TaskStates.
-	if len(ar.state.TaskStates) == 0 {
+	if len(state.TaskStates) == 0 {
 		ar.tasksLock.RLock()
 		ar.state.TaskStates = make(map[string]*structs.TaskState, len(ar.tasks))
 		for k, tr := range ar.tasks {
-			ar.state.TaskStates[k] = tr.TaskState()
+			state.TaskStates[k] = tr.TaskState()
 		}
 		ar.tasksLock.RUnlock()
 	}
 
-	return ar.state.Copy()
+	return state
 }
 
 // Update the running allocation with a new version received from the server.