例子：
var __global lock; // 注意加__global是为了能在多线程中可访问

function main() {
    console.log('main start');
    lock = new Lock();
    var t = new Thread();
    t.start(func);

    lock.lock();
    console.log('main enter lock');
    sleep(5000);
    console.log('main leave lock');
    lock.unlock();

    console.log('main end');
}

function func() {
    console.log('func start');
    lock.lock();
    console.log('func enter lock');
    sleep(5000);
    console.log('func leave lock');
    lock.unlock();
    console.log('func end');
}