lumbda/www/repl/worker.mjs

// wasm/app/worker.mjs
// Tier-evaluation Web Worker. Keeps the main thread responsive so the
// live ms counter actually ticks AND so cancel works (main thread
// terminates this worker via worker.terminate()).

import { evalOnTier, setBendUrl, setPauseFlag, heapStats, portalSave, portalLoad } from "./runner.js";

self.onmessage = async (e) => {
    const { kind } = e.data;
    if (kind === "config") {
        // Each field is independently optional so a config message can
        // tweak one knob without resetting the others — REPL spawns
        // workers with just { pauseFlag }; playground updates bendUrl
        // alone, etc.
        if (e.data.bendUrl !== undefined) setBendUrl(e.data.bendUrl);
        if (e.data.pauseFlag !== undefined) setPauseFlag(e.data.pauseFlag);
        return;
    }
    if (kind === "heap") {
        // Synchronous read — no eval is running because the worker is
        // single-threaded and main thread only sends this between evals.
        self.postMessage({ kind: "heap", runId: e.data.runId, tier: e.data.tier, stats: heapStats(e.data.tier) });
        return;
    }
    if (kind === "portal-save") {
        // Pulls the most-recent /tmp/<name>.portal out of the tier's
        // MEMFS after the lisp side ran (portal-snapshot! NAME). Main
        // thread encrypts and stuffs it into the vault.
        const blob = portalSave(e.data.tier, e.data.name);
        self.postMessage({ kind: "portal-save", runId: e.data.runId, name: e.data.name, blob });
        return;
    }
    if (kind === "portal-load") {
        // Hydrates MEMFS from a vault-decrypted blob so a subsequent
        // (portal-load! NAME) eval finds the file ready.
        const ok = portalLoad(e.data.tier, e.data.name, e.data.blob);
        self.postMessage({ kind: "portal-load", runId: e.data.runId, name: e.data.name, ok });
        return;
    }
    if (kind !== "eval") return;
    const { runId, tier, src } = e.data;
    // Buffer chunks on the worker side so a tight (display ...) loop
    // doesn't fire one postMessage per glyph. Without batching, a
    // 100M-iteration display loop generated hundreds of millions of
    // messages that left the main thread too busy to even register
    // click events — fox reported the tab "kept looping when I left
    // it" because the tab-switch click couldn't be dispatched. The
    // 64KB / 4096-line thresholds coalesce the tight-loop case down
    // by ~50000x while still flushing fast enough that short outputs
    // feel real-time (the first flush fires once the buffer crosses
    // the threshold, so a 50-line print appears as soon as the eval
    // finishes via the drain-at-end path). We can't use a wall-clock
    // timer to flush because the wasm eval runs synchronously inside
    // the worker — no event loop tick happens between Module.print
    // calls.
    const CHUNK_FLUSH_BYTES = 65536;
    const CHUNK_FLUSH_NEWLINES = 4096;
    // Wall-clock flush — guarantees the first emission lands on the UI
    // immediately and caps low-rate streams at ~10 flushes/sec. Without
    // this, a (let loop ...) that emits every 10K iterations would
    // accumulate 30 bytes per emit, take 2000+ emits to hit the 64KB
    // threshold, and the user sees nothing for seconds. lastFlushTime
    // starts at 0 so the first chunk to land always triggers a flush.
    const FLUSH_INTERVAL_MS = 100;
    let chunkBuffer = "";
    let chunkNewlines = 0;
    let lastFlushTime = 0;
    function flushChunkBuffer() {
        if (!chunkBuffer) return;
        self.postMessage({ kind: "chunk-batch", runId, tier, text: chunkBuffer });
        chunkBuffer = "";
        chunkNewlines = 0;
        lastFlushTime = Date.now();
    }
    try {
        const output = await evalOnTier(
            tier,
            src,
            (loadingTier) => {
                self.postMessage({ kind: "loading", runId, tier: loadingTier });
            },
            (chunk) => {
                if (!chunk) return;
                chunkBuffer += chunk;
                for (let i = 0; i < chunk.length; i++) {
                    if (chunk.charCodeAt(i) === 10) chunkNewlines++;
                }
                if (chunkBuffer.length >= CHUNK_FLUSH_BYTES
                    || chunkNewlines >= CHUNK_FLUSH_NEWLINES
                    || (Date.now() - lastFlushTime) >= FLUSH_INTERVAL_MS) {
                    flushChunkBuffer();
                }
            },
        );
        // Drain whatever the chunk callback left in the buffer before
        // the eval returned — last lines of a program would otherwise
        // never reach the UI.
        flushChunkBuffer();
        self.postMessage({ kind: "done", runId, output });
    } catch (err) {
        flushChunkBuffer();
        self.postMessage({ kind: "error", runId, message: err && err.message ? err.message : String(err) });
    }
};