Use unrolled list as a pool with current ref

Author: tshemsedinov

JavaScript/7-current.js

@@ -0,0 +1,114 @@
+'use strict';
+
+class QueueNode {
+  length = 0;
+
+  constructor({ size }) {
+    this.size = size;
+    this.buffer = new Array(size).fill(null);
+    this.reset();
+  }
+
+  reset() {
+    this.readIndex = 0;
+    this.writeIndex = 0;
+    this.next = null;
+  }
+
+  enqueue(item) {
+    if (this.writeIndex >= this.size) return false;
+    this.buffer[this.writeIndex++] = item;
+    this.length++;
+    return true;
+  }
+
+  dequeue() {
+    if (this.length === 0) return null;
+    const index = this.readIndex++;
+    const item = this.buffer[index];
+    this.buffer[index] = null;
+    this.length--;
+    return item;
+  }
+}
+
+class UnrolledQueue {
+  #length = 0;
+  #nodeSize = 1024;
+  #poolSize = 2;
+  #head = null;
+  #tail = null;
+  #current = null;
+
+  constructor(options = {}) {
+    const { nodeSize, poolSize } = options;
+    if (nodeSize) this.#nodeSize = nodeSize;
+    if (poolSize) this.#poolSize = poolSize;
+
+    let first = new QueueNode({ size: nodeSize });
+    let node = first;
+    for (let i = 1; i < poolSize; i++) {
+      node.next = new QueueNode({ size: nodeSize });
+      node = node.next;
+    }
+    node.next = first;
+
+    this.#head = first;
+    this.#current = first;
+    this.#tail = node;
+  }
+
+  get length() {
+    return this.#length;
+  }
+
+  enqueue(item) {
+    if (!this.#head.enqueue(item)) {
+      if (this.#head.next === this.#current) {
+        const node = new QueueNode(this.#nodeSize);
+        node.next = this.#head.next;
+        this.#head.next = node;
+        if (this.#tail === this.#head) this.#tail = node;
+      }
+      this.#head = this.#head.next;
+      this.#head.enqueue(item);
+    }
+    this.#length++;
+  }
+
+  dequeue() {
+    if (this.#length === 0) return null;
+    const item = this.#current.dequeue();
+    this.#length--;
+    if (this.#current.length === 0 && this.#current !== this.#head) {
+      const node = this.#current;
+      this.#current = this.#current.next;
+      node.reset();
+      this.#tail.next = node;
+      this.#tail = node;
+    }
+    return item;
+  }
+}
+
+// Usage
+
+const mq = new UnrolledQueue({ nodeSize: 8, poolSize: 2 });
+
+for (let id = 0; id < 5; id++) {
+  mq.enqueue({ id });
+}
+
+while (mq.length) {
+  const task = mq.dequeue();
+  console.log(`Processing ${task.id}`);
+}
+
+for (let id = 100; id < 105; id++) {
+  mq.enqueue({ id });
+}
+
+while (mq.length) {
+  const task = mq.dequeue();
+  console.log(`Processing ${task.id}`);
+}