Date: Wed, 8 Mar 2006 11:26:59 GMT From: Peter Edwards <peadar@FreeBSD.org> To: freebsd-gnats-submit@FreeBSD.org Subject: java/94223: Timing bug affecting java.lang.Object.wait(long millis) Message-ID: <200603081126.k28BQxWq095376@www.freebsd.org> Resent-Message-ID: <200603081130.k28BU4Kk021536@freefall.freebsd.org>
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>Number: 94223
>Category: java
>Synopsis: Timing bug affecting java.lang.Object.wait(long millis)
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-java
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Mar 08 11:30:04 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator: Peter Edwards
>Release: -stable, -current
>Organization:
FreeBSD
>Environment:
FreeBSD caveman.vordel.com 6.0-STABLE FreeBSD 6.0-STABLE #1: Thu Feb 2 14:58:08 GMT 2006 petere@caveman.vordel.com:/usr/obj/usr/6-STABLE/src/sys/CAVEMAN i386
>Description:
There's a bug in compute_abstime in hotspot/src/os/bsd/vm/os_bsd.hpp: when normalising a "struct timespec", and incrementing the seconds due to overflow of nanoseconds, the nanoseconds count is incorrectly adjusted, sometimes leading to a ~1 second overestimate of the amount of time to sleep for.
This affects java.lang.Object.wait(long millis) at a minimum.
>How-To-Repeat:
$ cat > T.java << .
> public class T {
> public static void main(String[] args) {
> try {
> T t = new T();
> t.run();
> }
> catch (Exception e) {
> e.printStackTrace();
> }
> }
>
> synchronized void run() throws InterruptedException {
> long then = System.currentTimeMillis();
> for (;;) {
> wait(100);
> long now = System.currentTimeMillis();
> System.out.println("diff: " + (now - then) + "\t(abs " + now + ")");
> then = now;
> }
> }
> }
> .
$ /usr/local/jdk1.5.0/bin/javac T
$ /usr/local/jdk1.5.0/bin/java T
diff: 101 (abs 1141816614685)
diff: 103 (abs 1141816614788)
diff: 102 (abs 1141816614890)
diff: 102 (abs 1141816614992)
diff: 1009 (abs 1141816616001)
diff: 102 (abs 1141816616103)
diff: 102 (abs 1141816616205)
diff: 102 (abs 1141816616307)
diff: 102 (abs 1141816616409)
diff: 102 (abs 1141816616511)
diff: 102 (abs 1141816616613)
diff: 102 (abs 1141816616715)
diff: 102 (abs 1141816616817)
diff: 102 (abs 1141816616919)
diff: 1082 (abs 1141816618001)
diff: 102 (abs 1141816618103)
diff: 102 (abs 1141816618205)
diff: 102 (abs 1141816618307)
diff: 102 (abs 1141816618409)
diff: 105 (abs 1141816618514)
diff: 102 (abs 1141816618616)
diff: 102 (abs 1141816618718)
diff: 102 (abs 1141816618820)
diff: 102 (abs 1141816618922)
diff: 1079 (abs 1141816620001)
>Fix:
os_bsd.hpp, line 351: this:
if (nsec >= 1000000000) {
abstime->tv_sec += 1;
nsec -= 1000000;
}
should be this:
if (nsec >= 1000000000) {
abstime->tv_sec += 1;
nsec -= 1000000000;
}
>Release-Note:
>Audit-Trail:
>Unformatted:
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