[crac] RFR: Correct System.nanotime() value after restore [v6]

[Jan Kratochvil]

On Fri, 12 May 2023 06:01:45 GMT, Radim Vansa <duke at openjdk.org> wrote:

>> Besides discussion of this patch vs. native CRIU timens support I find easier (YMMV) and less error-prone to just use simple `LD_PRELOAD`+`RTLD_NEXT` to simulate the system reboots: https://stackoverflow.com/a/6083624/2995591
>
> I agree with your line of thinking, and since this test actually uses custom docker image I can add those libraries to the base image. But in general it's a problem of criu packaging with implicit dependencies, officially installed binary should get this handled in dependency management. Since those few functions from libbsd are reimplemented in criu, we could just disable the dependency in our fork.
> However we'll run into the same problem with libnftables - I found that with the nftables support the unprivileged restore as root in Docker container does not work anymore. And that got compiled in only because of the -dev library present, there's no compile time switch.
> 
> The error you describe can be solved with `git clean -f -x`, regrettably `make clean` does not do its job very well.
> 
> Not sure what function are you suggesting to replace?

I mean to provide normal LD_PRELOAD library and then one no longer needs to deal with any containers with their associated problems discussed above.
[libvirtual.c.txt](https://github.com/openjdk/crac/files/11465377/libvirtual.c.txt)
[clock_gettime.cpp.txt](https://github.com/openjdk/crac/files/11465400/clock_gettime.cpp.txt)

rm -rf dir;mkdir dir;LD_PRELOAD=$PWD/libvirtual.so CLOCK_MONOTONIC=10 BOOT_ID=$PWD/fake_boot_id ./clock_gettime &p=$!;sleep 2;sudo ./build/linux-x86_64-server-fastdebug/jdk/lib/criu dump --shell-job -t $p -D dir
CLOCK_MONOTONIC=88547. 87286504 CLOCK_BOOTTIME=88547. 87304536
CLOCK_MONOTONIC=88548. 87433771 CLOCK_BOOTTIME=88548. 87445951
CLOCK_MONOTONIC=88549. 87564393 CLOCK_BOOTTIME=88549. 87573859
Warn  (criu/pages-compress.c:216): decompress: Can't open 'pages-1.comp.img' for dfd=3, errno=2 [--- that is some bug]
CLOCK_MONOTONIC=10.    82447 CLOCK_BOOTTIME=88556.959892251
CLOCK_MONOTONIC=11.   179010 CLOCK_BOOTTIME=88557.959969582
CLOCK_MONOTONIC=12.   264924 CLOCK_BOOTTIME=88558.960056407

With original JVM it correctly crashes:

#  Internal Error (../../src/hotspot/share/runtime/thread.cpp:2470), pid=74780, tid=74781
#  assert(false) failed: unexpected time moving backwards detected in JavaThread::sleep()

With your patch it runs although somehow slowly.
It may need some adjustments, I wrote the library as a proof of concept to prevent the containers.
One cannot use the library to test native CRIU timens as that happens at kernel-level.

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PR Review Comment: https://git.openjdk.org/crac/pull/53#discussion_r1192482912