Atomics.xor() In JavaScript

What is Atomics?

• The Atomics is an object in JavaScript that provides the ability to perform atomic operations as static methods.
• Just like the Math object in JavaScript all the properties and methods of Atomics are also static.
• Atomics are used with SharedArrayBuffer(generic fixed-length binary data buffer) objects.
• Atomics are not constructors like other global objects.
• Atomics cannot be used with a new operator or can be invoked as a function.

Atomics Operations in JavaScript Multiple threads can read and write the same data in memory when there shared memory is. To ensure that predicted values are written and read accurately, another operation cannot start until and unless the current one finishes. Atomic operations also cannot be interrupted. 

Atomics.xor() Method

• Among the Atomic Operations, there is an inbuilt operation Atomics.xor() in JavaScript that is used to compute a bitwise XOR with a given value at a given position in the array.
• Atomics.xor() operation returns the old value at that position.
• The integer typedarray, index, and the value are passed as an argument to the function and it returns the value that has been stored in the respective array.

Syntax:

Atomics.xor(typedArray, index, value)

Parameters Used:

1. typedarray: It is the shared integer typed array Int8Array, Uint8Array, Int16Array etc.
2. index: It is the position in the typedArray to compute bitwise XOR.
3. value: The number to compute bitwise XOR with.

Return value: Atomics.xor() returns the old value at the given position(typedArray[index]). Examples of the above function are given below: Examples:

Input : arr[0] = 7
        Atomics.xor(arr, 0, 2)
Output : 5

Input : arr[0] = 4
        Atomics.xor(arr, 0, 3)
Output : 7

Code for the above function are provided below: Code 1:

javascript

// creating a SharedArrayBuffer
let buf = new SharedArrayBuffer(16);
let arr = new Uint8Array(buf);

// Initialising element at zeroth position of
//array with 7
arr[0] = 7;

// Displaying the SharedArrayBuffer
console.log(Atomics.load(arr, 0));

// Displaying the return value of the
//Atomics.xor() method
console.log(Atomics.xor(arr, 0, 2));

// Displaying the updated SharedArrayBuffer
console.log(Atomics.load(arr, 0));

OUTPUT:

7
5
5

Code 2:

javascript

// creating a SharedArrayBuffer
let buf = new SharedArrayBuffer(25);
let arr = new Uint8Array(buf);

// Initialising element at zeroth position
//of array with 3
arr[0] = 3

// Displaying the SharedArrayBuffer
console.log(Atomics.load(arr, 0));

// Displaying the return value of the
//Atomics.xor() method
console.log(Atomics.xor(arr, 0, 5));

// Displaying the updated SharedArrayBuffer
console.log(Atomics.load(arr, 0));

OUTPUT:

3
6
6

Application: Whenever we want to compute bitwise XOR with any value and want to return the computed value, we use Atomics.xor() operation in JavaScript. Let’s see a JavaScript Program : 

javascript

// creating a SharedArrayBuffer
let mybuffer = new SharedArrayBuffer(25);
let myarray = new Uint8Array(mybuffer);

// Initialising the element at zeroth position of array
myarray[0] = 15;

// Displaying the return value of the Atomics.xor() method
console.log(Atomics.xor(myarray, 0, 10));

// Displaying the updated SharedArrayBuffer
console.log(Atomics.load(myarray, 0));

OUTPUT:

5
5

Exceptions:

• If the typedArray is not one of the allowed integer types then the Atomics.xor( ) operation throws a TypeError.
• If the typedArray is not a shared typed array then the Atomics.xor( ) operation throws a TypeError.
• If the index used as an argument to the Atomics.xor( ) operation is out of the bound in the typedArray then the Atomics.store( ) operation throws a RangeError.