fix: limit number of bb.js threads to 32 (#9070)

This PR pulls out the limiting of the number of threads from #8861
without the other changes which are failing CI.

barretenberg/acir_tests/browser-test-app/src/index.ts

@@ -2,7 +2,7 @@ import createDebug from "debug";
 import { inflate } from "pako";
 
 createDebug.enable("*");
-const debug = createDebug("simple_test");
+const debug = createDebug("browser-test-app");
 
 async function runTest(
   bytecode: Uint8Array,

barretenberg/ts/src/barretenberg/backend.ts

@@ -16,16 +16,6 @@ export class UltraPlonkBackend {
   /** @ignore */
   async instantiate(): Promise<void> {
     if (!this.api) {
-      if (typeof navigator !== 'undefined' && navigator.hardwareConcurrency) {
-        this.options.threads = navigator.hardwareConcurrency;
-      } else {
-        try {
-          const os = await import('os');
-          this.options.threads = os.cpus().length;
-        } catch (e) {
-          console.log('Could not detect environment. Falling back to one thread.', e);
-        }
-      }
       const api = await Barretenberg.new(this.options);
 
       const honkRecursion = false;
@@ -125,16 +115,6 @@ export class UltraHonkBackend {
   /** @ignore */
   async instantiate(): Promise<void> {
     if (!this.api) {
-      if (typeof navigator !== 'undefined' && navigator.hardwareConcurrency) {
-        this.options.threads = navigator.hardwareConcurrency;
-      } else {
-        try {
-          const os = await import('os');
-          this.options.threads = os.cpus().length;
-        } catch (e) {
-          console.log('Could not detect environment. Falling back to one thread.', e);
-        }
-      }
       const api = await Barretenberg.new(this.options);
       const honkRecursion = true;
       await api.acirInitSRS(this.acirUncompressedBytecode, honkRecursion);

barretenberg/ts/src/barretenberg/verifier.ts

@@ -18,17 +18,6 @@ export class BarretenbergVerifier {
   /** @ignore */
   async instantiate(): Promise<void> {
     if (!this.api) {
-      if (typeof navigator !== 'undefined' && navigator.hardwareConcurrency) {
-        this.options.threads = navigator.hardwareConcurrency;
-      } else {
-        try {
-          const os = await import('os');
-          this.options.threads = os.cpus().length;
-        } catch (e) {
-          console.log('Could not detect environment. Falling back to one thread.', e);
-        }
-      }
-
       const api = await Barretenberg.new(this.options);
       await api.initSRSForCircuitSize(0);
 

barretenberg/ts/src/barretenberg_wasm/index.ts

@@ -7,12 +7,30 @@ import { fetchCode } from './fetch_code/index.js';
 
 const debug = createDebug('bb.js:wasm');
 
-export async function fetchModuleAndThreads(desiredThreads?: number) {
+export async function fetchModuleAndThreads(desiredThreads = 32) {
   const shared = getSharedMemoryAvailable();
-  const threads = shared ? desiredThreads : 1;
+
+  const availableThreads = shared ? await getAvailableThreads() : 1;
+  // We limit the number of threads to 32 as we do not benefit from greater numbers.
+  const limitedThreads = Math.min(desiredThreads, availableThreads, 32);
+
   const code = await fetchCode(shared);
   const module = await WebAssembly.compile(code);
-  return { module, threads };
+  return { module, threads: limitedThreads };
+}
+
+async function getAvailableThreads(): Promise<number> {
+  if (typeof navigator !== 'undefined' && navigator.hardwareConcurrency) {
+    return navigator.hardwareConcurrency;
+  } else {
+    try {
+      const os = await import('os');
+      return os.cpus().length;
+    } catch (e) {
+      debug(`Could not detect environment. Falling back to one thread.: {e}`);
+      return 1;
+    }
+  }
 }
 
 export class BarretenbergWasm extends BarretenbergWasmMain {