Concurrency & Delay in Node.js

Understand how JavaScript handles delays, asynchronous execution, concurrency, parallelism, workers, and thread safety.

Waiting & Asynchronous Execution

JavaScript is single-threaded but can schedule delayed and asynchronous operations using the event loop.

1. Wait for N milliseconds

Non-blocking delay.

2. Run a Function Asynchronously

Schedule execution.

Coordinating Asynchronous Operations

Promises allow coordination between multiple asynchronous operations.

1. Wait for Multiple Async Functions

Promise.all

2. Wait for At Least One Async Function

Promise.race

Promise Chaining: then, catch & finally

Promises provide then, catch, and finally methods to control asynchronous execution flow without using async/await. This style is still widely used and important to understand.

1. then(): Handling Successful Completion

Access resolved value.

2. catch(): Handling Errors

Centralized error handling.

3. finally(): Cleanup Logic

Runs regardless of outcome.

4. Chaining Multiple then Calls

Sequential async flow.

5. then/catch vs async/await

Choosing the right style.

Passing Data Between Async & Sync Code

Asynchronous functions return Promises which carry data back to synchronous code.

1. Passing Data from Async Function

Promise result.

Timers & Intervals

JavaScript provides timers for delayed and repeated operations.

1. Perform Operation After Delay

setTimeout

2. Perform Operation at Every Interval

setInterval

Measuring Time Intervals

Time measurement helps in profiling and performance optimization.

1. Calculating Time Interval

Using Date.now

Parallel Execution using Workers

JavaScript normally runs on a single thread, but Workers allow true parallel execution by running code on separate threads. This is critical for performance and responsiveness.

1. Node.js Worker Threads

Running CPU-heavy work on a separate OS thread.

2. Web Workers (JavaScript)

Parallel execution in browser environments.

Thread Safety & Mutex

When multiple asynchronous operations access the same variable, race conditions can occur. A mutex ensures that only one operation can access a critical section at a time.

1. Race Condition Problem

Multiple async tasks modifying shared state.

2. Mutex Implementation

Allow only one async operation at a time.

3. Using Mutex to Protect Shared State

Prevent race conditions.

4. When Should You Use a Mutex?

Practical guidance.