Date: Tue, 11 Apr 2017 17:28:12 -0500 From: Eric van Gyzen <eric@vangyzen.net> To: redraiment@gmail.com, freebsd-java@freebsd.org Cc: Konstantin Belousov <kostikbel@gmail.com> Subject: Re: OpenJDK8 Thread.sleep will deadlock while turn down system date time. Message-ID: <a48038a5-3f12-f7ef-9e94-6c33b4672c02@vangyzen.net> In-Reply-To: <20170408070340.GD1788@kib.kiev.ua> References: <CAPRzLQSOfySJWqN8CoLNchRs_JgHkeQz57ZNB9E__Meip3zmOQ@mail.gmail.com> <20170408070340.GD1788@kib.kiev.ua>
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On 4/8/17 2:03 AM, Konstantin Belousov wrote:
> On Fri, Apr 07, 2017 at 08:12:42PM -0700, ????????? wrote:
>> Hi all,
>>
>> I found a Java process deadlock issue, and can be reproduced in FreeBSD
>> 10.3 and 11.0 .
>>
>> My environment:
>>
>> * VirutalBox 5.1.16 r113841 on Mac OS X 10.12.4
>> * FreeBSD-11.0-RELEASE-amd64.vhd.xz
>>
>> Reproduction steps:
>>
>> 1. install openjdk8
>>
>> ```sh
>> pkg install openjdk8
>> ```
>>
>> 2. Java source code
>>
>> ```java
>> public class Main {
>> public static void main(String[] args) {
>> while (true) {
>> System.out.println("tick");
>> Thread.sleep(3000);
>> }
>> }
>> }
>> ```
>>
>> 3. Run java
>>
>> ```sh
>> $ javac Main.java
>> $ java Main
>> tick
>> tick
>> ...
>> ```
>>
>> 4. Turn down system date time.
>>
>> ```sh
>> $ date '+%Y-%m-%d %H:%M:%S'
>> 20170408 11:09:11
>> $ date 201001010000
>> Fri Jan 1 00:00:00 CST 2010
>> ```
>>
>> Then, the java process will hung.
> Hang != deadlock, why do you claim that the process deadlocked.
>>
>> The issue will reproduce while turn "DOWN" the date time. It's OK while
>> turn up the date time.
>
> If JVM sets timeouts using absolute times than it might be fixed in latest
> HEAD and stable/11.
The JVM uses pthread_cond_timedwait() to implement Thread.sleep(), so it
always uses absolute times. Furthermore, it uses the default clock,
CLOCK_REALTIME. My recent change (r315280) does not fix this behavior;
in fact, I believe it will make the problem worse, since moving the
clock forward will wake the thread prematurely.
I think the JVM should be fixed to use CLOCK_MONOTONIC. Would someone
like to do the research to determine the correct behavior of
Thread.sleep()? Specifically, should the duration of the sleep be
affected by adjustments to the real-time clock? I expect that it should
/not/ be affected, especially since the API takes a relative/interval
time. Ideally, we would find the answer in the formal language
specification; failing that, I would be satisfied with empirical data
from testing on Windows, Linux, MacOS, and Solaris. I'll be happy to
write a patch once we know what it should do.
Please keep me CC'd, since I'm not on freebsd-java@. (Thanks for the
CC, Kostik.)
Eric
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