⚡ Bolt: Optimize StringEncoder with direct encodeInto

.jules/bolt.md

@@ -0,0 +1,6 @@
+## 2026-01-19 - Avoid Intermediate Buffers with TextEncoder
+**Learning:** TextEncoder.encodeInto works directly with Uint8Array views on SharedArrayBuffer. Intermediate buffers and copying are unnecessary and can double the execution time.
+**Action:** Check TextEncoder usage for direct writing to destination buffers.
+## 2026-01-20 - Optimize Read Performance with Zero-Copy
+**Learning:** TextDecoder can sometimes decode directly from SharedArrayBuffer views, but browser support varies. Feature detection is required. NumberEncoder (DataView) always supports SAB but requires respecting byteOffset.
+**Action:** Use feature detection for TextDecoder and fix DataView offsets to enable zero-copy reads.

src/array/ShareableArray.ts

@@ -3,6 +3,7 @@ import {Serializable} from "../encoding";
 import StringEncoder from "../encoding/StringEncoder";
 import NumberEncoder from "../encoding/NumberEncoder";
 import GeneralPurposeEncoder from "../encoding/GeneralPurposeEncoder";
+import {SUPPORTS_SAB_VIEW_DECODE} from "../utils/featureDetection";
 import {TransferableState} from "../TransferableState";
 import TransferableDataStructure from "../TransferableDataStructure";
 
@@ -884,14 +885,22 @@ export class ShareableArray<T> extends TransferableDataStructure {
         // Find the correct value encoder and decode the value at the requested position in the data array
         const encoder = this.getEncoderById(valueEncoderId);
 
-        // Copy from shared memory to a temporary private buffer (since we cannot directly decode from shared memory)
         const sourceView = new Uint8Array(this.dataView.buffer, dataPos + ShareableArray.DATA_OBJECT_OFFSET, valueLength);
 
-        const targetView = new Uint8Array(this.getFittingDecoderBuffer(valueLength), 0, valueLength);
-        targetView.set(sourceView);
+        // Optimization: For NumberEncoder (ID 0), we can always read directly from shared memory (via DataView).
+        // For others (String/General), we check if TextDecoder supports SAB views.
+        // We avoid direct reads for custom serializers (ID 3) as we can't guarantee they handle SAB views correctly.
+        const canReadDirectly = valueEncoderId === 0 || ((valueEncoderId === 1 || valueEncoderId === 2) && SUPPORTS_SAB_VIEW_DECODE);
 
+        if (canReadDirectly) {
+            return encoder.decode(sourceView);
+        } else {
+            // Copy from shared memory to a temporary private buffer (since we cannot directly decode from shared memory)
+            const targetView = new Uint8Array(this.getFittingDecoderBuffer(valueLength), 0, valueLength);
+            targetView.set(sourceView);
 
-        return encoder.decode(targetView);
+            return encoder.decode(targetView);
+        }
     }
 
     private deleteItem(index: number): void {

src/encoding/NumberEncoder.ts

@@ -2,7 +2,8 @@ import Serializable from "./Serializable";
 
 export default class NumberEncoder implements Serializable<number> {
     decode(buffer: Uint8Array): number {
-        const bufferView = new DataView(buffer.buffer);
+        // Create DataView respecting the byteOffset of the input buffer (which might be a view into a larger buffer)
+        const bufferView = new DataView(buffer.buffer, buffer.byteOffset, buffer.byteLength);
 
         // First byte indicates if we did store a float or an int
         const numberType = bufferView.getUint8(0);

src/map/ShareableMap.ts

@@ -3,6 +3,7 @@ import Serializable from "./../encoding/Serializable";
 import StringEncoder from "./../encoding/StringEncoder";
 import NumberEncoder from "./../encoding/NumberEncoder";
 import GeneralPurposeEncoder from "./../encoding/GeneralPurposeEncoder";
+import {SUPPORTS_SAB_VIEW_DECODE} from "../utils/featureDetection";
 import ShareableMapOptions from "./ShareableMapOptions";
 import {TransferableState} from "../TransferableState";
 import TransferableDataStructure from "../TransferableDataStructure";
@@ -730,6 +731,10 @@ export class ShareableMap<K, V> extends TransferableDataStructure {
 
         const sourceView = new Uint8Array(this.dataView.buffer, startPos + ShareableMap.DATA_OBJECT_OFFSET, keyLength);
 
+        if (SUPPORTS_SAB_VIEW_DECODE) {
+            return this.textDecoder.decode(sourceView);
+        }
+
         const targetView = new Uint8Array(this.getFittingDecoderBuffer(keyLength), 0, keyLength);
         targetView.set(sourceView);
 
@@ -757,11 +762,20 @@ export class ShareableMap<K, V> extends TransferableDataStructure {
         const keyLength = this.dataView.getUint32(startPos + 4);
         const valueLength = this.dataView.getUint32(startPos + 8);
 
-        const encoder = this.getEncoderById(this.dataView.getUint16(startPos + 14));
+        const valueEncoderId = this.dataView.getUint16(startPos + 14);
+        const encoder = this.getEncoderById(valueEncoderId);
 
-        // Copy from shared memory to a temporary private buffer (since we cannot directly decode from shared memory)
         const sourceView = new Uint8Array(this.dataView.buffer, startPos + ShareableMap.DATA_OBJECT_OFFSET + keyLength, valueLength);
 
+        // Optimization: For NumberEncoder (ID 0), we can always read directly from shared memory.
+        // For others, we check if TextDecoder supports SAB views.
+        const canReadDirectly = valueEncoderId === 0 || ((valueEncoderId === 1 || valueEncoderId === 2) && SUPPORTS_SAB_VIEW_DECODE);
+
+        if (canReadDirectly) {
+            return encoder.decode(sourceView);
+        }
+
+        // Copy from shared memory to a temporary private buffer (since we cannot directly decode from shared memory)
         const targetView = new Uint8Array(this.getFittingDecoderBuffer(valueLength), 0, valueLength);
         targetView.set(sourceView);
 

src/utils/featureDetection.ts

@@ -0,0 +1,13 @@
+
+export const SUPPORTS_SAB_VIEW_DECODE = (() => {
+    try {
+        if (typeof SharedArrayBuffer === 'undefined') return false;
+        // Create a small SharedArrayBuffer and try to decode a view of it
+        const sab = new SharedArrayBuffer(1);
+        const view = new Uint8Array(sab);
+        new TextDecoder().decode(view);
+        return true;
+    } catch (e) {
+        return false;
+    }
+})();