Examples of why atomics are necessary

atomics.zig

const std = @import("std");

var global: u32 = 0;

export fn normalStore(arg: u32) void {
    global = arg;
}

export fn normalLoad() u32 {
    return global;
}

export fn volatileStore(arg: u32) void {
    @ptrCast(*volatile u32, &global).* = arg;
}

export fn volatileLoad() u32 {
    return @ptrCast(*volatile u32, &global).*;
}

export fn atomicStoreMonotonic(val: u32) void {
    @atomicStore(u32, &global, val, .Monotonic);
}

export fn atomicStoreRelease(val: u32) void {
    @atomicStore(u32, &global, val, .Release);
}

export fn atomicStoreSeqCst(val: u32) void {
    @atomicStore(u32, &global, val, .SeqCst);
}

export fn atomicLoadMonotonic() u32 {
  return @atomicLoad(u32, &global, .Monotonic);
}

export fn atomicLoadAcquire() u32 {
    return @atomicLoad(u32, &global, .Acquire);
}

export fn atomicLoadSeqCst() u32 {
    return @atomicLoad(u32, &global, .SeqCst);
}