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Date:      Thu, 12 Nov 2015 20:17:30 +0400
From:      Sergey Potapov <sp@smartspb.net>
To:        freebsd-java@freebsd.org
Subject:   Thread.sleep is very incorrect on kern.hz FreeBSD-10 + openjdk8.
Message-ID:  <5644BB9A.4060807@smartspb.net>
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[-- Attachment #1 --]
Hello!

FreeBSD-10.1 without tunning.
openjdk8     without tunning (pkg install).


Thread.sleep depends on kern.hz sysctl variable.

Simple program and more detailed version information attched.
openjdk7 tested with kern.hz=2000 -- same results.

kern.hz: 100

1000 times Thread.sleep(1)                           19994 milliseconds
1000 times Thread.sleep(2)                           19997 milliseconds
1000 times TimeUnit.MICROSECONDS.sleep(100)          20000 milliseconds

kern.hz: 1000

1000 times Thread.sleep(1)                            2002 milliseconds
1000 times Thread.sleep(2)                            3000 milliseconds
1000 times TimeUnit.MICROSECONDS.sleep(100)           2001 milliseconds


kern.hz: 2000

1000 times Thread.sleep(1)                            1500 milliseconds
1000 times Thread.sleep(2)                            2500 milliseconds
1000 times TimeUnit.MICROSECONDS.sleep(100)           1500 milliseconds

Linux and Windows are much better (but don't support anything less 1ms too).

Linux:

sysctl: cannot stat /proc/sys/kern/hz: No such file or directory.

1000 times Thread.sleep(1)                            1077 milliseconds
1000 times Thread.sleep(2)                            2078 milliseconds
1000 times TimeUnit.MICROSECONDS.sleep(100)           1079 milliseconds

Windows (with sysctl command removed):

1000 times Thread.sleep(1)                            1002 milliseconds
1000 times Thread.sleep(2)                            2000 milliseconds
1000 times TimeUnit.MICROSECONDS.sleep(100)           1002 milliseconds

--
Sergey Potapov.



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