问题
The TimeUnit.sleep(long timeout) documentation describes its argument thus:
timeout - the minimum time to sleep.
However, I'm finding that — at least on Windows 7 64-bit with Java 8 update 141 — the thread often sleeps for less than the minimum:
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!"));
}
}
Typical output:
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!
This seems to contradict the documentation. However, the TimeUnit doc also states that TimeUnit.sleep() is a convenience wrapper for Thread.sleep, and the latter doesn't say if it guarantees to sleep at least the specified amount.
Is this an API implementation error, or is TimeUnit.sleep and/or Thread.sleep designed to only sleep for approximately, rather than at least, the specified duration?
回答1:
TimeUnit.sleep() delegates to Thread.sleep().
Thread.sleep() is subject to the precision and accuracy of system timers and schedulers, thus TimeUnit.sleep() will not be as accurate as you may need.
来源：https://stackoverflow.com/questions/45419940/java-thread-sleep-for-minimum-time