java - 如果删除 printf，应用程序将无法正常工作

Question

我有一个让我发疯的 Contiki 应用程序。

我必须计算 Tmote Sky 的能量消耗。我正在使用energest，这是我在能耗估算功能中使用的一段代码，它被定期调用:

lpm_time = energest_type_time(ENERGEST_TYPE_LPM);
cpu_time = energest_type_time(ENERGEST_TYPE_CPU);
rx_time = energest_type_time(ENERGEST_TYPE_LISTEN);
tx_time = energest_type_time(ENERGEST_TYPE_TRANSMIT);
lpm = lpm_time - prev_times.lpm_time;
cpu = cpu_time - prev_times.cpu_time;
rx = rx_time - prev_times.rx_time;
tx = tx_time - prev_times.tx_time;

consumed_energy = (I_LPM * lpm + I_CPU * cpu + I_RX * rx + I_TX * tx) * VOLTS / RTIMER_ARCH_SECOND;  /* mJ = mA * seconds * volts */

/*printf("lpm %lu, cpu %lu, rx %lu, tx %lu, prl %lu, prc %lu, prr %lu, prt %lu\n",
       lpm_time, cpu_time, rx_time, tx_time, prev_times.lpm_time, prev_times.cpu_time, prev_times.rx_time, prev_times.tx_time);*/

prev_times.lpm_time = lpm_time;
prev_times.cpu_time = cpu_time;
prev_times.rx_time = rx_time;
prev_times.tx_time = tx_time;

问题是应用程序只有在启用现在被注释的 printf 时才能正常工作。如果它保持原样注释，我可能会收到无意义的 consumed_energy 变量值，或者 COOJA 模拟停止并显示 Java Illegal read - out of bounds 消息。

为什么会这样？？？可能是什么原因？这是一件很奇怪的事情。

提前致谢。

---

这个文件的完整代码是这样的:

volatile static struct energest_times prev_times;


float update_consumption()
{
    uint32_t lpm_time;
    uint32_t cpu_time;
    uint32_t rx_time;
    uint32_t tx_time;
    uint32_t lpm;
    uint32_t cpu;
    uint32_t rx;
    uint32_t tx;
    float consumed_energy;

    lpm_time = energest_type_time(ENERGEST_TYPE_LPM);
    cpu_time = energest_type_time(ENERGEST_TYPE_CPU);
    rx_time = energest_type_time(ENERGEST_TYPE_LISTEN);
    tx_time = energest_type_time(ENERGEST_TYPE_TRANSMIT);
    lpm = lpm_time - prev_times.lpm_time;
    cpu = cpu_time - prev_times.cpu_time;
    rx = rx_time - prev_times.rx_time;
    tx = tx_time - prev_times.tx_time;

    consumed_energy = (I_LPM * lpm + I_CPU * cpu + I_RX * rx + I_TX * tx) * VOLTS / RTIMER_ARCH_SECOND;  /* mJ = mA * seconds * volts */

    printf("lpm %lu, cpu %lu, rx %lu, tx %lu, prl %lu, prc %lu, prr %lu, prt %lu\n",
            lpm_time, cpu_time, rx_time, tx_time, prev_times.lpm_time, prev_times.cpu_time, prev_times.rx_time, prev_times.tx_time);

    prev_times.lpm_time = lpm_time;
    prev_times.cpu_time = cpu_time;
    prev_times.rx_time = rx_time;
    prev_times.tx_time = tx_time;

    printf("Consumed energy: %ld\n", (int32_t) consumed_energy);

    return consumed_energy;
}

该函数被另一个函数周期性地调用，每分钟一次。

Answer 1

您可以在 Java 或 C 中看到这一点，如果您有多个线程使用非线程安全的库。在这种情况下，有时您会得到正确的值，有时您只对了一半，有时您会胡说八道。

如果您添加一个 printf，例如System.out.printf() 或任何 IO 或 sleep() 或使用调试逐步执行代码，这确实会减慢您的应用程序，因此每个线程在库中花费的时间只有很小一部分，从而间接避免了冲突。

您是否使用多线程？您调用的库/方法是线程安全的吗？