Internal Design

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