Vala 中委托的异步作用域是什么？

Question

我正在尝试async examples from the GNOME project site。我收到以下警告，我不明白如何解决。

async.vala:8.2-8.17: warning: delegates with scope="async" must be owned

代码

async double do_calc_in_bg(double val) throws ThreadError {
    SourceFunc callback = do_calc_in_bg.callback;
    double[] output = new double[1];

    // Hold reference to closure to keep it from being freed whilst
    // thread is active.
    // WARNING HERE
    ThreadFunc<bool> run = () => {
        // Perform a dummy slow calculation.
        // (Insert real-life time-consuming algorithm here.)
        double result = 0;
        for (int a = 0; a<100000000; a++)
            result += val * a;

        output[0] = result;
        Idle.add((owned) callback);
        return true;
    };
    new Thread<bool>("thread-example", run);

    yield;
    return output[0];
}

void main(string[] args) {
    var loop = new MainLoop();
    do_calc_in_bg.begin(0.001, (obj, res) => {
            try {
                double result = do_calc_in_bg.end(res);
                stderr.printf(@"Result: $result\n");
            } catch (ThreadError e) {
                string msg = e.message;
                stderr.printf(@"Thread error: $msg\n");
            }
            loop.quit();
        });
    loop.run();
}

警告指向异步函数内的run 变量。谁或什么需要拥有？对闭包的引用？

Answer 1

代理需要始终有一个明确定义的所有者。错误信息有点误导。

要修复它，您必须将所有权从委托显式转移到线程构造函数：

new Thread<bool>("thread-example", (owned) run);

而不是

new Thread<bool>("thread-example", run);

另请参阅：https://wiki.gnome.org/Projects/Vala/Tutorial#Ownership

PS：生成的 C 代码在这两种情况下都很好。 （至少使用 valac 0.46.6）