perf(troika-three-text): parallelize SDF generation with multiple wor…

…ker threads

Since the SDF generation worker no longer contains expensive font parsing state,
it is lightweight enough to spawn in multiple workers for parallelization.
Currently uses a max of 4 worker threads, which are terminated after an idle
timeout, for 3-4x overall performance increase in the SDF generation phase.

packages/troika-three-text/src/TextBuilder.js

@@ -1,5 +1,5 @@
 import { Color, DataTexture, LinearFilter, RGBAFormat } from 'three'
-import { defineWorkerModule, ThenableWorkerModule, Thenable } from 'troika-worker-utils'
+import { defineWorkerModule, terminateWorker, ThenableWorkerModule, Thenable } from 'troika-worker-utils'
 import { createSDFGenerator } from './worker/SDFGenerator.js'
 import { createTypesetter } from './worker/Typesetter.js'
 import { createGlyphSegmentsIndex } from './worker/GlyphSegmentsIndex.js'
@@ -353,52 +353,52 @@ const typesetterWorkerModule = /*#__PURE__*/defineWorkerModule({
   }
 })
 
-// Fan-out to multiple worker threads: (TODO? needs analysis.)
-// let generateSDFInWorker = function(...args) {
-//   const threadCount = 2
-//   const workers = []
-//
-//   let callNum = 0
-//   generateSDFInWorker = function(...args) {
-//     const workerIdx = (callNum++) % threadCount
-//     if (!workers[workerIdx]) {
-//       workers[workerIdx] = defineWorkerModule({
-//         name: 'SDFGenerator_' + workerIdx,
-//         workerId: 'TroikaTextSDF_' + workerIdx,
-//         dependencies: [
-//           CONFIG,
-//           createGlyphSegmentsIndex,
-//           createSDFGenerator
-//         ],
-//         init(config, createGlyphSegmentsIndex, createSDFGenerator) {
-//           const {sdfExponent, sdfMargin} = config
-//           return createSDFGenerator(createGlyphSegmentsIndex, { sdfExponent, sdfMargin })
-//         },
-//         getTransferables(result) {
-//           return [result.textureData.buffer]
-//         }
-//       })
-//     }
-//     return workers[workerIdx](...args)
-//   }
-//   return generateSDFInWorker(...args)
-// }
-
-const generateSDFInWorker = /*#__PURE__*/defineWorkerModule({
-  name: 'SDFGenerator',
-  dependencies: [
-    CONFIG,
-    createGlyphSegmentsIndex,
-    createSDFGenerator
-  ],
-  init(config, createGlyphSegmentsIndex, createSDFGenerator) {
-    const {sdfExponent, sdfMargin} = config
-    return createSDFGenerator(createGlyphSegmentsIndex, { sdfExponent, sdfMargin })
-  },
-  getTransferables(result) {
-    return [result.textureData.buffer]
+/**
+ * SDF generator function wrapper that fans out requests to a number of worker
+ * threads for parallelism
+ */
+const generateSDFInWorker = /*#__PURE__*/function() {
+  const threadCount = 4 //how many workers to spawn
+  const idleTimeout = 2000 //workers will be terminated after being idle this many milliseconds
+  const threads = {}
+  let callNum = 0
+  return function(...args) {
+    const workerId = 'TroikaTextSDFGenerator_' + ((callNum++) % threadCount)
+    let thread = threads[workerId]
+    if (!thread) {
+      thread = threads[workerId] = {
+        workerModule: defineWorkerModule({
+          name: workerId,
+          workerId,
+          dependencies: [
+            CONFIG,
+            createGlyphSegmentsIndex,
+            createSDFGenerator
+          ],
+          init(config, createGlyphSegmentsIndex, createSDFGenerator) {
+            const {sdfExponent, sdfMargin} = config
+            return createSDFGenerator(createGlyphSegmentsIndex, { sdfExponent, sdfMargin })
+          },
+          getTransferables(result) {
+            return [result.textureData.buffer]
+          }
+        }),
+        requests: 0,
+        idleTimer: null
+      }
+    }
+
+    thread.requests++
+    clearTimeout(thread.idleTimer)
+    return thread.workerModule(...args)
+      .then(result => {
+        if (--thread.requests === 0) {
+          thread.idleTimer = setTimeout(() => { terminateWorker(workerId) }, idleTimeout)
+        }
+        return result
+      })
   }
-})
+}()
 
 const typesetInWorker = /*#__PURE__*/defineWorkerModule({
   name: 'Typesetter',