Starvation

Microtask Starvation

Introduction

If microtasks keep queuing new microtasks, the macrotask queue never gets processed. This is called starvation.

The Problem

// ⚠️ Microtasks keep queuing new microtasks
function loop() {
  queueMicrotask(() => {
    console.log('Microtask');
    loop(); // Keeps adding more microtasks
  });
}

loop();

setTimeout(() => {
  console.log('This may never run!');
}, 100);
// Macrotasks get starved by infinite microtasks

Why This Matters

In real applications, promise chains could accidentally starve the event loop:

async function processItems(items) {
  for (const item of items) {
    // Each await adds a microtask
    await Promise.resolve().then(() => processItem(item));
  }
}
// This might delay rendering and user interactions

Prevention

// Yield to the event loop periodically
async function processItems(items) {
  for (const item of items) {
    processItem(item); // Synchronous processing
    if (item.index % 100 === 0) {
      await new Promise(resolve => setTimeout(resolve, 0)); // Yield
    }
  }
}

Summary

Microtasks run continuously until the queue is empty
Infinite microtask loops starve macrotasks
setTimeout, rendering, and I/O can be delayed
Yield periodically in long microtask chains

Starvation

Microtask Starvation

Introduction

The Problem

Why This Matters

Prevention

Summary

Further Reading