SharedArrayBuffer for shared memory in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What does SharedArrayBuffer enable in Node.js?

Which of the following best describes the purpose of SharedArrayBuffer in Node.js?

A It creates isolated memory copies for each thread to avoid conflicts.

B It encrypts data automatically when shared between threads.

C It allows multiple threads to share the same memory space for faster data exchange.

D It manages asynchronous file system operations efficiently.

💡 Hint

Think about how threads can communicate without copying data.

SharedArrayBuffer provides a way for multiple threads to access the same memory area, enabling fast communication without copying data.

❓ component_behavior

intermediate

What is the output of this Node.js code using SharedArrayBuffer?

Consider the following code snippet. What will be logged to the console?

Node.js

const sab = new SharedArrayBuffer(4);
const int32 = new Int32Array(sab);
int32[0] = 42;
console.log(int32[0]);

A 42

B undefined

C 0

D Throws a TypeError

💡 Hint

Check how Int32Array views the SharedArrayBuffer.

The Int32Array views the SharedArrayBuffer as an array of 32-bit integers. Setting int32[0] to 42 stores that value, so logging it outputs 42.

📝 Syntax

advanced

Which option correctly creates a SharedArrayBuffer of 16 bytes and a Uint8Array view?

Select the code snippet that correctly creates a SharedArrayBuffer of 16 bytes and a Uint8Array view over it.

A

const sab = new SharedArrayBuffer();
const view = new Uint8Array(sab, 16);

B

const sab = SharedArrayBuffer(16);
const view = Uint8Array(sab);

C

const sab = new SharedArrayBuffer(16);
const view = new Uint8Array();

D

const sab = new SharedArrayBuffer(16);
const view = new Uint8Array(sab);

💡 Hint

Remember the correct syntax for constructors in JavaScript.

Option D correctly uses the new keyword and passes the buffer to the typed array constructor.

🔧 Debug

advanced

Why does this code throw a RangeError?

Given the code below, why does it throw a RangeError?

Node.js

const sab = new SharedArrayBuffer(8);
const view = new Int32Array(sab, 4, 2);
console.log(view.length);

A The byteOffset 4 plus length 2 exceeds the buffer size of 8 bytes.

B Int32Array cannot be created from SharedArrayBuffer.

C The length parameter must be omitted when byteOffset is specified.

D SharedArrayBuffer size must be a multiple of 16 bytes.

💡 Hint

Calculate total bytes needed: byteOffset + length * bytes per element.

The Int32Array elements are 4 bytes each. Starting at byte 4 with length 2 requires 8 bytes total, but the buffer size is only 8 bytes, so it tries to access beyond the buffer.

❓ state_output

expert

What is the final value of sharedArray[0] after two workers increment it?

Assume two worker threads share a SharedArrayBuffer with an Int32Array view named sharedArray. Each worker runs this code once: Atomics.add(sharedArray, 0, 1); If the initial value of sharedArray[0] is 0, what is the final value after both workers finish?

A 0

B 2

C Undefined due to race condition

D 1

💡 Hint

Atomics methods ensure safe updates even with multiple threads.

Using Atomics.add guarantees atomic increments, so both increments are counted, resulting in 2.