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Multithreading, Concurrency: A Deep Dive with JavaScript
This article discusses how javascript handle Multithreading and Concurrency
rahulvijayvergiya.hashnode.dev
Ever wondered how your computer handles multiple tasks at once? Whether it's running multiple apps, loading web pages, or processing data, it all comes down to multithreading and concurrency.
But what exactly do these terms mean, and how do they work? Let’s break it down in a way that’s easy to understand, with a special focus on how JavaScript—despite being single-threaded—handles concurrency like a pro.
What is Multithreading?
Multithreading allows a CPU or program to execute multiple threads simultaneously. A thread is the smallest unit of execution within a process, and multithreading helps in parallelising tasks, leading to better performance and resource efficiency.
Key Concepts in Multithreading
Thread – A lightweight unit of execution within a process.
Process – A running program with its own memory space.
Thread Scheduling – The operating system decides which thread runs when.
Context Switching – Storing the state of one thread while switching to another.
Why Use Multithreading?
🚀 Performance Boost – Multiple tasks run in parallel.
🏗️ Efficient Resource Use – Threads share memory, reducing overhead.
🖥️ Responsive Applications – Keeps UI applications smooth and lag-free.
🔬 Parallel Computing – Great for CPU-heavy tasks like AI, simulations, and gaming.
Challenges of Multithreading
Race Conditions – Multiple threads accessing shared data can cause unpredictable behavior.
Deadlocks – Threads waiting indefinitely for each other to release resources.
Synchronisation Overhead – Managing shared resources requires extra work (locks, semaphores, mutexes, etc.).
What is Concurrency?
Concurrency is about managing multiple tasks at the same time, but not necessarily executing them in parallel. A system that supports concurrency can switch between tasks efficiently, even if it has only one thread.
Key Concepts in Concurrency
Asynchronous Execution – Tasks run without blocking each other.
Event Loop – A single-threaded mechanism to handle multiple operations efficiently.
Non-Blocking I/O – Prevents slow I/O operations from blocking execution.
Task Scheduling – Determines the execution order of different tasks.
Why Concurrency Matters?
🔄 Faster Execution – Keeps applications running smoothly by handling multiple tasks efficiently.
🌍 Better Scalability – Essential for handling many client requests in web applications.
⚡ Non-Blocking Performance – Ideal for real-time apps like chat, gaming, and video streaming.
Challenges of Concurrency
Synchronisation Issues – Ensuring correct execution order can be tricky.
Data Races – Tasks modifying shared data at the same time can lead to conflicts.
Debugging Complexity – Bugs related to concurrency are often hard to trace.
Multithreading and Concurrency in JavaScript
JavaScript is single-threaded by design, meaning it executes one task at a time. However, it achieves concurrency using an event-driven, non-blocking architecture powered by the event loop.
How JavaScript Manages Concurrency
Event Loop – Manages async operations efficiently.
Callbacks & Promises – Allow non-blocking execution.
Async/Await – A cleaner syntax for handling asynchronous code.
Web Workers – Enable multithreading in JavaScript.
Example: Concurrency in JavaScript
console.log("Start");
setTimeout(() => {
console.log("Async Task Completed");
}, 2000);
console.log("End");
Output:
Start
End
Async Task Completed (after 2 seconds)
Even though setTimeout is scheduled first, JavaScript doesn’t wait for it to complete—it moves on to the next task. The event loop ensures smooth execution without blocking.
Using Web Workers for Multithreading in JavaScript
// main.js
const worker = new Worker("worker.js");
worker.onmessage = function(event) {
console.log("Message from Worker:", event.data);
};
worker.postMessage("Hello Worker");
// worker.js
onmessage = function(event) {
postMessage("Worker received: " + event.data);
};
Web Workers let JavaScript run scripts in background threads, preventing the main thread from getting blocked by heavy computations.
Conclusion
While JavaScript doesn’t support traditional multithreading, it leverages event-driven concurrency to handle multiple tasks efficiently. If you need actual parallel execution, Web Workers can help!
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