LYR-SEM0213

a module 'var' in a program that starts threads

warning · spec 10-concurrency · lint global-var-without-sync, group concurrency, warn unless said

A module of a program that imports std.thread declares a module-level var.

Explanation

Tasks of one thread take turns, but threads run at once: two of them may read and write a module's var at the same time, and a value half written is read.

Hold the value in an Atomic, or behind a Mutex (std.sync), or keep it local to one thread. A var that a lock of its own guards says so with @Allow("global-var-without-sync").

Wrong

import std.thread { Thread };

var hits = 0;

fn main(): void {
    hits = hits + 1;
    let _ = Thread.spawn(() => 1);
}

Right

import std.thread { Thread };

fn main(): void {
    var hits = 0;
    hits = hits + 1;
    let _ = hits;
    let _ = Thread.spawn(() => 1);
}