wpilibsuite / frc-openjdk-roborio

OpenJDK builds for FRC RoboRIO

frc-openjdk

This is a roboRIO ipk package builder for the OpenJDK JRE.

The roboRIO ipk uses the ARM 32bit JRE for ARMv7 soft float ABI.

Building

On any Unix system, simply run ./build-docker to build the package.

frc-openjdk-roborio's Issues

wrong version in packaging?

versions.sh calls out 6aa6f6860508 which looks to correspond to jdk-11.0.12+5. However, it's packaged as 11.0.9u12-1

Reentrant `synchronized` usage causing deadlock

Hi All,

Bottom line:
Starting in 2022, (v2022-11.0.9u12-1 and on) if you have multiple threads calling a synchronized function which then acquires another synchronized lock, there is a small (but very present) likelihood of deadlock. This deadlock does not happen with earlier roboRIO JRE versions or on my workstation.

Affected java versions:

admin@roboRIO-176-FRC:/home/lvuser# /usr/local/frc/JRE/bin/java --version
openjdk 11.0.12.12-frc 2021-07-20
OpenJDK Runtime Environment (build 11.0.12.12-frc+0-2022-11.0.9u12-1)
OpenJDK Client VM (build 11.0.12.12-frc+0-2022-11.0.9u12-1, mixed mode)

admin@roboRIO-176-FRC:~# /usr/local/frc/JRE/bin/java --version
openjdk 11.0.12.5-frc 2021-07-20
OpenJDK Runtime Environment (build 11.0.12.5-frc+0-2022-11.0.12u5-1)
OpenJDK Client VM (build 11.0.12.5-frc+0-2022-11.0.12u5-1, mixed mode)

Please see attached proof-of-concept Main.java.txt and thread_dump.txt

Steps to reproduce:

1. On a roboRIO with FRC_roboRIO_2022_v4.0 using GradleRIO version 2022.3.1 (and thus openjdk 11.0.12.5-frc 2021-07-20)
2. Deploy the proof-of-concept Main.java.txt
3. You should see output that resembles

Starting!
7402115
10125555
10125555
10125555
10125555

4. Run kill -3 <pid of java process> to acquire a thread dump. It should look similar to the one attached.
5. Install 2021's release of the FRC JRE: v2021-11.0.9u11-1
6. After restarting the robot code, you should see output that resembles

Starting!
2469866
4920792
7393729
...
24649211
27119381
29589939
30000000
Starting!
2468994
4965939
7437033
...

Notes:

1. Originally I tried using older FRC images (FRC_roboRIO_2020_v10 and FRC_roboRIO_2021_v3.0) and their respective GradleRIO versions, but then narrowed it down to the JRE as I could install an older version and reproduce previous behavior
2. This does not occur if you disable threads 2 and 3
3. This also does not occur if you remove the synchronized block from setSum()
4. Workaround: replacing synchronized with a ReentrantReadWriteLock and locking the critical sections in the same way, this does not happen

Thanks,
Kyle Z
Software Mentor
Team 176 - Aces High

Main.java.txt
thread_dump.txt