Improved poolify

tshemsedinov · tshemsedinov · commit 6d8791cac7ba · 2018-01-10T08:11:03.000+02:00
- Support function instantiation
- Optimize returns
- Use setImmediate to be async
diff --git a/JavaScript/6-poolify.js b/JavaScript/6-poolify.js
@@ -0,0 +1,83 @@
+'use strict';
+
+const poolified = Symbol('poolified');
+
+const mixFlag = { [poolified]: true };
+
+const duplicate = (factory, n) => (
+  new Array(n).fill().map(() => {
+    const instance = factory();
+    return Object.assign(instance, mixFlag);
+  })
+);
+
+const provide = callback => item => {
+  setImmediate(() => {
+    callback(item);
+  });
+};
+
+const poolify = (factory, min, norm, max) => {
+  let allocated = norm;
+  const pool = (par) => {
+    if (par[poolified]) {
+      const delayed = pool.delayed.shift();
+      if (delayed) delayed(par);
+      else pool.items.push(par);
+      return;
+    }
+    const callback = provide(par);
+    if (pool.items.length < min && allocated < max) {
+      const grow = Math.min(max - allocated, norm - pool.items.length);
+      allocated += grow;
+      const items = duplicate(factory, grow);
+      pool.items.push(...items);
+    }
+    const res = pool.items.pop();
+    if (res) callback(res);
+    else pool.delayed.push(callback);
+  };
+  return Object.assign(pool, {
+    items: duplicate(factory, norm),
+    delayed: []
+  });
+};
+
+// Usage
+
+const adder = a => b => adder(a + b);
+
+const pool = poolify(adder, 1, 2, 3);
+
+console.log('request Item1');
+pool(item1 => {
+  console.log('get Item1');
+  console.log('request Item2');
+  pool(item2 => {
+    console.log('get Item2');
+    console.log('request Item3');
+    pool(item3 => {
+      console.log('get Item3');
+      setTimeout(() => {
+        pool(item3);
+        console.log('recycle Item3');
+      }, 50);
+    });
+    console.log('request Item4');
+    pool(item4 => {
+      console.log('get Item4');
+      setTimeout(() => {
+        pool(item4);
+        console.log('recycle Item4');
+      }, 20);
+    });
+    setTimeout(() => {
+      pool(item1);
+      console.log('recycle Item1');
+      setTimeout(() => {
+        pool(item2);
+        console.log('recycle Item2');
+      }, 10);
+    }, 10);
+  });
+});
