Method background_try_lock

thread/thread.cpp:502–520

            wait_while(background_locked);
        }
        bool background_try_lock() {
            while(true) {
                // wait if (unlikely) foreground locked
                wait_while(foreground_locked);

                // try lock
                if (background_locked.exchange(true, std::memory_order_acquire))
                    return false;   // avoid wait while holding the lock

                // check to make sure it is still unlocked
                if (likely(!foreground_locked.load(std::memory_order_acquire)))
                    return true;

                // otherwise release lock, wait, and repeat again
                background_locked.store(false, std::memory_order_release);
                spin_wait();
            }
            return true;
        }
        void foreground_unlock() {
            foreground_locked.store(false, std::memory_order_release);
        }