阻行模式【其他模式】

阻行设计模式

public class Balking {
    /**
     *  balking design pattern【阻行设计模式】：
     *  当目标对象不在特定状态时，执行阻行方法时，该方法会立即返回不执行任何操作。
     */
    @Test
    public void all() throws InterruptedException {
        final int count = 3;
        final Machine machine = new Machine();
        for (int i = 0; i < count; i++) {
            CompletableFuture.runAsync(() -> {
                try {
                    machine.tryRun();
                } catch (final InterruptedException e) {
                }
            });
        }
        TimeUnit.SECONDS.sleep(5);
    }
}

enum MachineState {
    IDLE, WORKING
}

@Slf4j
class Machine {
    private MachineState state = MachineState.IDLE;

    public void tryRun() throws InterruptedException {
        synchronized (this) {
            if (MachineState.WORKING.equals(state)) {
                log.error("machine is working now");
                return;
            }
            state = MachineState.WORKING;
        }
        log.info("machine is working for {}", Thread.currentThread().getName());
        TimeUnit.SECONDS.sleep(2);
        finish();
    }

    private synchronized void finish() {
        state = MachineState.IDLE;
        log.info("machine is idle now");
    }
}