Internal Design

pw_console: Multi-purpose pluggable interactive console for dev & manufacturing

Threads and Event Loops

In ptpython and IPython all user repl code is run in the foreground. This allows interrupts like Ctrl-C and functions like print() and time.sleep() to work as expected. Pigweed’s Console doesn’t use this approach as it would hide or freeze the prompt_toolkit user interface while running repl code.

To get around this issue all user repl code is run in a dedicated thread with stdout and stderr patched to capture output. This lets the user interface stay responsive and new log messages to continue to be displayed.

Here’s a diagram showing how pw_console threads and asyncio tasks are organized.

        flowchart LR
    classDef eventLoop fill:#e3f2fd,stroke:#90caf9,stroke-width:1px;
    classDef thread fill:#fffde7,stroke:#ffeb3b,stroke-width:1px;
    classDef plugin fill:#fce4ec,stroke:#f06292,stroke-width:1px;
    classDef builtinFeature fill:#e0f2f1,stroke:#4db6ac,stroke-width:1px;

    %% Subgraphs are drawn in reverse order.

    subgraph pluginThread [Plugin Thread 1]
        subgraph pluginLoop [Plugin Event Loop 1]
            toolbarFunc-->|"Refresh<br/>UI Tokens"| toolbarFunc
            toolbarFunc[Toolbar Update Function]
        end
        class pluginLoop eventLoop;
    end
    class pluginThread thread;

    subgraph pluginThread2 [Plugin Thread 2]
        subgraph pluginLoop2 [Plugin Event Loop 2]
            paneFunc-->|"Refresh<br/>UI Tokens"| paneFunc
            paneFunc[Pane Update Function]
        end
        class pluginLoop2 eventLoop;
    end
    class pluginThread2 thread;

    subgraph replThread [Repl Thread]
        subgraph replLoop [Repl Event Loop]
            Task1 -->|Finished| Task2 -->|Cancel with Ctrl-C| Task3
        end
        class replLoop eventLoop;
    end
    class replThread thread;

    subgraph main [Main Thread]
        subgraph mainLoop [User Interface Event Loop]
            log[[Log Pane]]
            repl[[Python Repl]]
            pluginToolbar([User Toolbar Plugin])
            pluginPane([User Pane Plugin])
            class log,repl builtinFeature;
            class pluginToolbar,pluginPane plugin;
        end
        class mainLoop eventLoop;
    end
    class main thread;

    repl-.->|Run Code| replThread
    pluginToolbar-.->|Register Plugin| pluginThread
    pluginPane-.->|Register Plugin| pluginThread2