Java Thread.sleep 最短时间

Question

timeout - the minimum time to sleep.

但是，我发现 — 至少在 Windows 7 64 位和 Java 8 更新 141 上 — 线程经常休眠 less 比最小值：

public static void main(String[] args) throws InterruptedException {
    final long from = TimeUnit.MILLISECONDS.toNanos(100);
    final long to   = TimeUnit.MILLISECONDS.toNanos(1000);
    final long step = TimeUnit.MILLISECONDS.toNanos(100);
    for (long requestedSleepDuration = from; requestedSleepDuration < to; requestedSleepDuration += step) {
        long sleepStartTime = System.nanoTime();
        TimeUnit.NANOSECONDS.sleep(requestedSleepDuration);
        long sleepEndTime = System.nanoTime();
        System.out.printf(
                "requested=%9d  actual=%9d  %s%n",
                requestedSleepDuration,
                sleepEndTime - sleepStartTime,
                (sleepEndTime - sleepStartTime >= requestedSleepDuration ? "OK" : " Slept less than minimum!"));
    }
}

典型输出：

requested=100000000  actual= 99534864  Slept less than minimum!
requested=200000000  actual=200063646  OK
requested=300000000  actual=299223086  Slept less than minimum!
requested=400000000  actual=399598620  Slept less than minimum!
requested=500000000  actual=499910360  Slept less than minimum!
requested=600000000  actual=600028523  OK
requested=700000000  actual=699604816  Slept less than minimum!
requested=800000000  actual=799230602  Slept less than minimum!
requested=900000000  actual=899490648  Slept less than minimum!

这似乎与文档相矛盾。然而，TimeUnit 文档还指出 TimeUnit.sleep() 是 Thread.sleep 的便利包装器，而后者没有说明它是否保证至少睡眠指定的数量。

这是 API 实施错误，还是 TimeUnit.sleep and/or Thread.sleep 设计为仅睡眠大约，而不是至少，指定的持续时间？

Answer 1

TimeUnit.sleep() 委托给 Thread.sleep().

Thread.sleep() 受制于系统计时器和调度程序的精度和准确度，因此 TimeUnit.sleep() 不会像您需要的那样准确。

Java Thread.sleep 最短时间

Java Thread.sleep for minimum time

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