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| -------------------------- MODULE CanvasRenderingBlocking -------------------------- | |
| EXTENDS FiniteSets, Integers, Sequences | |
| VARIABLES images_updated, display_lists_applied, compositor_messages, canvas_state | |
| CONSTANT N | |
| ---------------------------------------------------------------------------- | |
| Messages == {"DISPLAY_LIST", "UPDATE_IMAGE"} | |
| CanvasState == {"PENDING", "UPDATED"} | |
| TypeOk == /\ images_updated \in Int | |
| /\ display_lists_applied \in Int | |
| /\ compositor_messages \in Seq(Messages) | |
| /\ canvas_state \in CanvasState | |
| ImageUpdatesAndDisplayListsInSync == \/ images_updated = display_lists_applied | |
| \/ images_updated = display_lists_applied + 1 | |
| Init == /\ images_updated = 0 | |
| /\ display_lists_applied = 0 | |
| /\ compositor_messages = <<>> | |
| /\ canvas_state = "PENDING" | |
| \* Layout blocks on canvas update. | |
| LayoutSendsDisplayList == /\ compositor_messages' = Append(compositor_messages, "DISPLAY_LIST") | |
| /\ canvas_state = "UPDATED" | |
| /\ canvas_state' = "PENDING" | |
| /\ UNCHANGED<<images_updated, display_lists_applied>> | |
| CanvasSendsUpdateImage == | |
| \* Limiting model size with first two conditions. | |
| /\ images_updated < N | |
| /\ Len(compositor_messages) < 2 | |
| /\ compositor_messages' = Append(compositor_messages, "UPDATE_IMAGE") | |
| /\ canvas_state' = "UPDATED" | |
| /\ canvas_state = "PENDING" | |
| /\ UNCHANGED<<images_updated, display_lists_applied>> | |
| CompositorReceivesMessage == | |
| LET msg == Head(compositor_messages) | |
| IN /\ Len(compositor_messages) # 0 | |
| /\ CASE msg = "DISPLAY_LIST" -> | |
| /\ display_lists_applied' = display_lists_applied + 1 | |
| /\ UNCHANGED<<images_updated, canvas_state>> | |
| [] msg = "UPDATE_IMAGE" -> | |
| /\ images_updated' = images_updated + 1 | |
| /\ UNCHANGED<<display_lists_applied, canvas_state>> | |
| /\ compositor_messages' = Tail(compositor_messages) | |
| \* End with infinite stuttering steps. | |
| Done == /\ images_updated = N | |
| /\ UNCHANGED<<images_updated, | |
| display_lists_applied, | |
| compositor_messages, | |
| canvas_state>> | |
| Next == \/ LayoutSendsDisplayList | |
| \/ CanvasSendsUpdateImage | |
| \/ CompositorReceivesMessage | |
| \/ Done | |
| Spec == Init /\ [][Next]_<<images_updated, | |
| display_lists_applied, | |
| compositor_messages, | |
| canvas_state>> | |
| ---------------------------------------------------------------------------- | |
| THEOREM Spec => [](TypeOk /\ ImageUpdatesAndDisplayListsInSync) | |
| ============================================================================= |
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Results OK, with N = 3