colflow: clean up cancel flow fn retrieval

Not sure why but in the flow coordinator we were using a function that
returns a flow cancellation function. I believe the lazy evaluation is
not needed because `FlowBase.Setup` is called before we perform the
vectorized flow setup, so the proper cancellation function is available
when we need it.

Release note: None

pkg/sql/colflow/flow_coordinator.go

@@ -36,10 +36,8 @@ type FlowCoordinator struct {
 	row  rowenc.EncDatumRow
 	meta *execinfrapb.ProducerMetadata
 
-	// cancelFlow will return a function to cancel the context of the flow. It
-	// is a function in order to be lazily evaluated, since the context
-	// cancellation function is only available after the flow is Start()'ed.
-	cancelFlow func() context.CancelFunc
+	// cancelFlow cancels the context of the flow.
+	cancelFlow context.CancelFunc
 }
 
 var flowCoordinatorPool = sync.Pool{
@@ -57,7 +55,7 @@ func NewFlowCoordinator(
 	processorID int32,
 	input execinfra.RowSource,
 	output execinfra.RowReceiver,
-	cancelFlow func() context.CancelFunc,
+	cancelFlow context.CancelFunc,
 ) *FlowCoordinator {
 	f := flowCoordinatorPool.Get().(*FlowCoordinator)
 	f.input = input
@@ -155,7 +153,7 @@ func (f *FlowCoordinator) Next() (rowenc.EncDatumRow, *execinfrapb.ProducerMetad
 
 func (f *FlowCoordinator) close() {
 	if f.InternalClose() {
-		f.cancelFlow()()
+		f.cancelFlow()
 	}
 }
 

pkg/sql/colflow/vectorized_flow.go

@@ -1009,7 +1009,7 @@ func (s *vectorizedFlowCreator) setupOutput(
 			pspec.ProcessorID,
 			input,
 			s.syncFlowConsumer,
-			s.getCancelFlowFn,
+			s.getCancelFlowFn(),
 		)
 		// The flow coordinator is a root of its operator chain.
 		s.opChains = append(s.opChains, f)

pkg/sql/colflow/vectorized_flow_shutdown_test.go

@@ -364,7 +364,7 @@ func TestVectorizedFlowShutdown(t *testing.T) {
 					1, /* processorID */
 					materializer,
 					nil, /* output */
-					func() context.CancelFunc { return cancelLocal },
+					cancelLocal,
 				)
 				coordinator.Start(ctxLocal)