Limitation ‣ No shared memory in Electron - chung-leong/zigar GitHub Wiki

Electron no longer supports external buffers (see issue). The lack of shared memory makes it difficult to access Zig memory from JavaScript. Zigar uses a workaround to allow variables to function correctly. When the special properties dataView and typedArray bypass this workaround so they don't behave as you'd expect.

Consider the following example:

const std = @import("std");

pub var array: [4]i32 = .{ 1, 2, 3, 4 };

pub fn changeArray(index: usize, value: i32) void {
    array[index] = value;
}

require('node-zigar');
const test = require('../test.zig');

test.changeArray(0, 888);
const { typedArray } = test.array;
console.log(typedArray);
test.changeArray(1, 777);
console.log(typedArray);
console.log(test.array.typedArray);
console.log(typedArray);

Int32Array(4) [ 888, 2, 3, 4 ]
Int32Array(4) [ 888, 2, 3, 4 ]
Int32Array(4) [ 888, 777, 3, 4 ]
Int32Array(4) [ 888, 777, 3, 4 ]

Here test.array is not in possession of a shared memory buffer. It has a regular ArrayBuffer instead. When its typedArray property is accessed, values from the array in Zig are copied into this buffer. It then becomes out-of-date when array is modified through changeArray(). That's why the second line in the output is still Int32Array(4) [ 888, 2, 3, 4 ]. When typedArray is access again, the buffer is sync'ed once more and we finally see the change.

Modifying elements of typedArray has no effect on the array in Zig:

test.array.typedArray[3] = 333;
console.log(test.array.typedArray);

Int32Array(4) [ 888, 777, 3, 4 ]

An assignment to the typedArray does work:

test.array.typedArray = new Int32Array([ 4, 3, 2, 1 ]);

Int32Array(4) [ 4, 3, 2, 1 ]