Async Pool with await/await and timeout

JavaScript/a-await.js

@@ -0,0 +1,90 @@
+'use strict';
+
+class Pool {
+  constructor() {
+    this.items = [];
+    this.free = [];
+    this.queue = [];
+    this.current = 0;
+    this.size = 0;
+    this.available = 0;
+  }
+
+  async next() {
+    if (this.size === 0) return null;
+    if (this.available === 0) {
+      return new Promise((resolve) => {
+        this.queue.push(resolve);
+      });
+    }
+    let item = null;
+    let free = false;
+    do {
+      item = this.items[this.current];
+      free = this.free[this.current];
+      this.current++;
+    } while (!item || !free);
+    if (this.current === this.size) this.current = 0;
+    return item;
+  }
+
+  add(item) {
+    if (this.items.includes(item)) throw new Error('Pool: add duplicates');
+    this.size++;
+    this.available++;
+    this.items.push(item);
+    this.free.push(true);
+  }
+
+  async capture() {
+    const item = await this.next();
+    if (!item) return null;
+    const index = this.items.indexOf(item);
+    this.free[index] = false;
+    this.available--;
+    return item;
+  }
+
+  release(item) {
+    const index = this.items.indexOf(item);
+    if (index < 0) throw new Error('Pool: release unexpected item');
+    if (this.free[index]) throw new Error('Pool: release not captured');
+    this.free[index] = true;
+    this.available++;
+    if (this.queue.length > 0) {
+      const resolve = this.queue.shift();
+      if (resolve) setTimeout(resolve, 0, item);
+    }
+  }
+}
+
+// Usage
+
+(async () => {
+  const pool = new Pool();
+  pool.add({ item: 1 });
+  pool.add({ item: 2 });
+  const last = { item: 3 };
+  pool.add(last);
+
+  const x1 = await pool.capture();
+  console.log({ x1 });
+  const x2 = await pool.capture();
+  console.log({ x2 });
+  const x3 = await pool.capture();
+  console.log({ x3 });
+
+  pool.capture().then((x4) => {
+    console.log({ x4 });
+  });
+  pool.capture().then((x5) => {
+    console.log({ x5 });
+  });
+  pool.capture().then((x6) => {
+    console.log({ x6 });
+  });
+
+  pool.release(x2);
+  pool.release(x1);
+  pool.release(x3);
+})();

JavaScript/b-timeout.js

@@ -0,0 +1,102 @@
+'use strict';
+
+class Pool {
+  constructor(options = {}) {
+    this.items = [];
+    this.free = [];
+    this.queue = [];
+    this.timeout = options.timeout || 0;
+    this.current = 0;
+    this.size = 0;
+    this.available = 0;
+  }
+
+  async next() {
+    if (this.size === 0) return null;
+    if (this.available === 0) {
+      return new Promise((resolve, reject) => {
+        const waiting = { resolve, timer: null };
+        waiting.timer = setTimeout(() => {
+          waiting.resolve = null;
+          this.queue.shift();
+          reject(new Error('Pool next item timeout'));
+        }, this.timeout);
+        this.queue.push(waiting);
+      });
+    }
+    let item = null;
+    let free = false;
+    do {
+      item = this.items[this.current];
+      free = this.free[this.current];
+      this.current++;
+    } while (!item || !free);
+    if (this.current === this.size) this.current = 0;
+    return item;
+  }
+
+  add(item) {
+    if (this.items.includes(item)) throw new Error('Pool: add duplicates');
+    this.size++;
+    this.available++;
+    this.items.push(item);
+    this.free.push(true);
+  }
+
+  async capture() {
+    const item = await this.next();
+    if (!item) return null;
+    const index = this.items.indexOf(item);
+    this.free[index] = false;
+    this.available--;
+    return item;
+  }
+
+  release(item) {
+    const index = this.items.indexOf(item);
+    if (index < 0) throw new Error('Pool: release unexpected item');
+    if (this.free[index]) throw new Error('Pool: release not captured');
+    this.free[index] = true;
+    this.available++;
+    if (this.queue.length > 0) {
+      const { resolve, timer } = this.queue.shift();
+      clearTimeout(timer);
+      if (resolve) setTimeout(resolve, 0, item);
+    }
+  }
+}
+
+// Usage
+
+(async () => {
+  const pool = new Pool({ timeout: 5000 });
+  pool.add({ item: 1 });
+  pool.add({ item: 2 });
+  const last = { item: 3 };
+  pool.add(last);
+
+  const x1 = await pool.capture();
+  console.log({ x1 });
+  const x2 = await pool.capture();
+  console.log({ x2 });
+  const x3 = await pool.capture();
+  console.log({ x3 });
+
+  pool.capture().then((x4) => {
+    console.log({ x4 });
+  });
+  pool.capture().then((x5) => {
+    console.log({ x5 });
+  });
+  pool.capture().then((x6) => {
+    console.log({ x6 });
+  }).catch((err) => {
+    console.error({ err });
+  });
+
+  pool.release(x2);
+  pool.release(x1);
+  setTimeout(() => {
+    pool.release(x3);
+  }, 3000);
+})();