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My Experiences as a Beginner of OpenJDK Contributor (JCConf Taiwan 2021)
- 1. © 2021 NTT DATA Corporation My Experiences as a Beginner of OpenJDK Contributor 2021/11/19 JCConf Taiwan 2021 Koichi Sakata NTT DATA Corporation
- 2. About Me • Java Champion • OpenJDK Author • NTT DATA Corporation © 2021 NTT DATA Corporation 2 Koichi Sakata 阪田 浩一 jyukutyo
- 3. Our Contribution to JDK 17 © 2021 NTT DATA Corporation 3 The arrival of Java 17! https://blogs.oracle.com/java/post/announcing-java17
- 4. How to contribute to OpenJDK 1. Submit patches 2. Review code 3. Tell ideas 4. Participate in discussions 5. Make presentations 6. Write blog posts etc. © 2021 NTT DATA Corporation 4
- 5. How to contribute to OpenJDK 1. Submit patches 2. Review code 3. Tell ideas 4. Participate in discussions 5. Make presentations 6. Write blog posts etc. © 2021 NTT DATA Corporation 5 Today’s Focus
- 6. Contribution Process • Case: Bug Fix » Almost the same as popular OSS development © 2021 NTT DATA Corporation 6
- 7. Contribution Process • Case: Bug Fix » Almost the same as popular OSS development 1. Find a bug 2. Fix a bug 3. Submit a patch 4. Receive reviews 5. Address comments 6. Get merged © 2021 NTT DATA Corporation 7
- 8. Contribution Process • Case: Bug Fix » Almost the same as popular OSS development 1. ➡Find a bug 2. Fix a bug 3. Submit a patch 4. Receive reviews 5. Address comments 6. Get merged © 2021 NTT DATA Corporation 8
- 9. Can we find a bug? • OpenJDK works well in our applications » We hardly come across any new JDK bugs • Do we have no points to be fixed? © 2021 NTT DATA Corporation 9
- 10. Ways I’ve tried • How to find points to be fixed? 1. Build OpenJDK with new versions of tools © 2021 NTT DATA Corporation 10
- 11. Build with New Versions of Tools • OpenJDK has not only Java code but also C++ code • We can build OpenJDK with various tools on various platforms » GCC, Clang, Visual Studio » Linux, macOS, Windows (+WSL) • Errors or warnings might occur » Try to resolve when those occurred! © 2021 NTT DATA Corporation 11
- 12. My Experience • I used a new version of GCC (10.1) on Linux » Three new warnings occurred » I got an opportunity to contribute! © 2021 NTT DATA Corporation 12 In file included from /home/jyukutyo/code/jdk/src/hotspot/share/classfile/systemDictionary.hpp:31, from /home/jyukutyo/code/jdk/src/hotspot/share/classfile/javaClasses.hpp:28, from /home/jyukutyo/code/jdk/src/hotspot/share/precompiled/precompiled.hpp:35: In member function 'void Symbol::byte_at_put(int, u1)', inlined from 'Symbol::Symbol(const u1*, int, int)' at /home/jyukutyo/code/jdk/src/hotspot/share/oops/symbol.cpp:55:16: /home/jyukutyo/code/jdk/src/hotspot/share/oops/symbol.hpp:130:18: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=] 130 | _body[index] = value; | ~~~~~~~~~~~~~^~~~~~~ (omitted)
- 13. Changes in GCC 10 © 2021 NTT DATA Corporation 13 GCC 10 Release Series — Changes, New Features, and Fixes https://gcc.gnu.org/gcc-10/changes.html
- 14. Ways I’ve tried • How to find points to be fixed? 1. Build OpenJDK with new versions of tools 2. Search issues in JDK Bug System (JBS) © 2021 NTT DATA Corporation 14
- 15. JDK Bug System (JBS) • Bug tracking system for OpenJDK » https://bugs.openjdk.java.net/projects/JDK/issues/ © 2021 NTT DATA Corporation 15
- 16. Filter by Labels • Bug tracking system for OpenJDK » https://bugs.openjdk.java.net/projects/JDK/issues/ » Accessible for everyone with read-only » Filter issues by starter label • Those are for beginners • Clean-up label is also ok © 2021 NTT DATA Corporation 16
- 17. Ways I’ve tried • How to find points to be fixed? 1. Build OpenJDK with new versions of tools 2. Search issues in JDK Bug System (JBS) © 2021 NTT DATA Corporation 17
- 18. Contribution Process • Case: Bug Fix » Almost the same as popular OSS development 1. ✅Find a bug 2. ➡Fix a bug 3. Submit a patch 4. Receive reviews 5. Address comments 6. Get merged © 2021 NTT DATA Corporation 18
- 19. Testing is important • Assume that we've finished fixing code • Need to run related tests © 2021 NTT DATA Corporation 19
- 20. Testing is important • Assume that we've finished fixing code • Need to run related tests » For Java code: jtreg • Regression test harness • https://openjdk.java.net/jtreg/index.html © 2021 NTT DATA Corporation 20
- 21. Run a jtreg Test © 2021 NTT DATA Corporation 21
- 22. Testing is important • Run related tests before submitting the patch » For Java code: jtreg » For C++ code: gtest (GoogleTest) • Google C++ Testing Framework © 2021 NTT DATA Corporation
- 23. Testing is important • Run related tests before submitting the patch » For Java code: jtreg » For C++ code: gtest (GoogleTest) • Google C++ Testing Framework © 2021 NTT DATA Corporation $ ./build/linux-x86_64-server-fastdebug/hotspot/variant-server/libjvm/gtest/gtestLauncher -jdk:./build/linux- x86_64-server-fastdebug/jdk --gtest_filter=LogConfigurationTest.* Note: Google Test filter = LogConfigurationTest.* [==========] Running 15 tests from 1 test case. [----------] Global test environment set-up. [----------] 15 tests from LogConfigurationTest [ RUN ] LogConfigurationTest.describe_vm [ OK ] LogConfigurationTest.describe_vm (1 ms) (omitted) [==========] 15 tests from 1 test case ran. (659 ms total) [ PASSED ] 15 tests.
- 24. Contribution Process • Case: Bug Fix 1. ✅Find a bug 2. ✅Fix the bug 3. ➡ Submit a patch 4. Receive reviews 5. Address comments 6. Get merged © 2021 NTT DATA Corporation 24
- 25. First thing to do • Send a mail to a suitable ML » Describe the details of the issue » Paste the patch when you have already written it © 2021 NTT DATA Corporation 25
- 26. Mailing List • Always start from here » https://mail.openjdk.java.net/ © 2021 NTT DATA Corporation 26
- 27. Mailing List • Always start from here » https://mail.openjdk.java.net/ • Many MLs... © 2021 NTT DATA Corporation 27
- 28. Mailing List • Always start from here » https://mail.openjdk.java.net/ • Many MLs... » hotspot-dev - JVM » compiler-dev - Java compiler » core-libs-dev - Java class libraries » jdk-dev - General JDK discussions © 2021 NTT DATA Corporation 28
- 29. My First Mail © 2021 NTT DATA Corporation 29
- 30. My Experience • Do I send a patch to the public ML? » Feel uneasy... © 2021 NTT DATA Corporation 30
- 31. My Experience • Do I send a patch to the public ML? » Feel uneasy... » Don’t be afraid! • People are friendly and polite » To those who use English as a second language • like me © 2021 NTT DATA Corporation 31
- 32. As a Result • Have the issue filed in JBS » We are ready to create a pull request for the issue © 2021 NTT DATA Corporation 32
- 33. OpenJDK is now in GitHub © 2021 NTT DATA Corporation 33 https://github.com/openjdk/jdk
- 34. Relationship between JBS and GitHub • All issues need to be filed in JBS » Write the issue number in the title of the pull request • Comments to the PR is sent to related mailing lists » And vice versa © 2021 NTT DATA Corporation 34
- 35. Submit the Patch! • Sign OCA » Oracle Contribution Agreement » https://oca.opensource.oracle.com/ © 2021 NTT DATA Corporation 35
- 36. Submit the Patch! © 2021 NTT DATA Corporation 36 • Create a pull request
- 37. Contribution Process • Case: Bug Fix 1. ✅Find a bug 2. ✅Fix the bug 3. ✅Submit a patch 4. ➡Receive reviews 5. Address comments 6. Get merged © 2021 NTT DATA Corporation 37
- 38. Receive Reviews • Need reviews by Reviewers » Reviewer is a role in OpenJDK Community © 2021 NTT DATA Corporation 38
- 39. Receive Reviews • Need reviews by Reviewers » Reviewer is a role in OpenJDK Community • Roles » Reviewer - Committer role + review » Committer - Author role + commit and sponsor PRs » Author - edit JBS © 2021 NTT DATA Corporation 39 300+ Reviewers and Committers
- 40. Receive Reviews © 2021 NTT DATA Corporation 40
- 41. Contribution Process • Case: Bug Fix 1. ✅Find a bug 2. ✅Fix the bug 3. ✅Submit a patch 4. ✅Receive reviews 5. ✅Address comments 6. ➡Get merged © 2021 NTT DATA Corporation 41
- 42. Find a Sponsor • We can’t merge the PR by ourselves » Need a "sponsor" • Reviewer or Committer can sponsor PRs • Sponsor will merge the PR © 2021 NTT DATA Corporation 42
- 43. © 2021 NTT DATA Corporation 43
- 44. Finally... Case: Bug Fix 1. ✅Find a bug 2. ✅Fix the bug 3. ✅Submit a patch 4. ✅Receive reviews 5. ✅Address comments 6. ✅Get merged © 2021 NTT DATA Corporation 44
- 45. Summary • Don’t be afraid of submitting patches! » Contributing to OpenJDK is not difficult • Let’s move OpenJDK forward together! © 2021 NTT DATA Corporation 45
- 46. © 2021 NTT DATA Corporation All other company or product names mentioned here in are trademarks or registered trademarks of their respective owners.
Editor's Notes
- Thank you for your kind introduction ダゲーホー Hello everyone Thank you for joining me This is the title of my presentation
- Let me introduce myself I'm Koichi, Koichi Sakata I'm talking to you from Japan I show my handle name at the bottom left of this slide Follow me if you are interested I'm a Java Champion Last year I submitted some patches to OpenJDK, so I'm an OpenJDK Author now I work at NTT Data
- This chart shows issues fixed in JDK 17 per organization Our company, including me, has contributed to OpenJDK since before
- Today I will be taking about contributing to OpenJDK How many of you want to contribute to OpenJDK? Yes, I can see All people in this room want to do so As you can see, there are many ways of contributing When you hear of the contribution to open source software, the first thing that you think of is writing code But there are other ways to contribute It's good to combine some ways
- In this presentation, I will focus on the way of submitting patches Because this is the thing that most people are interested in, I think After this presentation, you will be able to submit patches to OpenJDK Duke needs you for JDK development
- Let's try to think about fixing bugs The contribution process is almost the same as developments of popular open source software, such as spring framework, Jakarta EE, etc.
- There are some steps to fix a bug First, find.., then fix..., submit..., finally the patch is merged I'll explain each step from now
- The first step is to find a bug
- As you know, OpenJDK works well in our applications almost always Have you ever come across a new JDK bug? We try to find bugs but failing to do so What should we do? Where are points to be fixed?
- I tried some different ways. As a result, I've found points to be fixed before. I'll introduce them to you. It's effective to build OpenJDK with new versions of tools
- As you may know, OpenJDK has not only Java but also C++, especially JVM is written in C++ So we need tools for C++ to build it For example we use GCC on Linux, Clang on macOS, Visual Studio on Windows You can build it on WSL, Windows Subsystem for Linux Errors or warnings might occur during the build. If those occurs, it means you have found the point to be fixed. Then you can try to resolve it
- I've actually tried it before I saw some warnings with GCC 10 immediately after it released Those warnings didn't happened with GCC 9 What you can see at the bottom is one of the warnings The details of the warning is out of this presentation When you build with the new versions of tools, you might be able to see some errors or warnings as well
- On the GCC website, I found those sentences in this slide The warning was enhanced in GCC 10 I examined the warning further and tried to change the code to fix the warning This is how I write a patch for warnings
- I'll introduce another way to find points to be fixed OpenJDK has the bug tracking system We simply call it JBS
- It's the bug tracking system JBS is based on Atlassian JIRA So you can operate JBS in the same way as JIRA. Look at this screenshot Each issue has detailed information
- JBS is accessible for everyone with read-only You can search issues on JBS In this screenshot I used the query language to search issues that have starter label Those are for beginners so good to address I’ve fixed some issues that had the label before Issues that have clean-up label are also good for beginners
- OK, we can find the points now Let's move on to the next step
- Second step is fixing a bug
- Assume that we've finished fixing code Of course, we should run tests before sending a patch
- Jtreg is the regression test harness I'll show you a demo
- This is the movie of running a jtreg test I increased the playback speed This code is a test class for the clhsdb tool in the jhsdb I executed the make run-test command It's running the test Just a moment What you can see here is the result of running a jtreg test
- There is also gtest test code for the C++ part Gtest is a Google C++ testing framework
- Here is the result of running a gtest test.
- So far, we become able to run tests Go on to the next step How do we submit our patch? Is it OK to create pull requests to the OpenJDK repository in GitHub?
- Instead of creating pull requests, it's better to send a mail to the suitable mailing lists. In the mail, you write the details of the issue you found and paste the patch if you have written it already When the issue is recognized, it is filed in JBS After that, you can create the pull request to the repository
- Mailing lists are important for the OpenJDK development. I'm going to talk for a minute about them
- Don't be surprised, OpenJDK has many mailing lists. I took a count of them There are 200 mailing lists
- I'll introduce a few of them hotspot-dev, compiler-dev... Each mailing list covers of the topic as described in this slide It's good to subscribe those mailing lists to gather information All mails are archived We can read past communications on the web site
- This is my first mail to the mailing list As you can see, it's about GCC warnings I explained before
- Yes, I understand how you feel now Do we need to code to the public mailing list? Everyone will feel uneasy to do I used to be the same
- But don't be afraid People in the OpenJDK community are friendly and polite Even if English is your second language, like me So you can send the mail, too
- When the issue is recognized, OpenJDK developers filed it in JBS After that, you can create a pull request in GitHub.
- OpenJDK has a repository in GitHub. It used to use Mercurial
- There is a relationship between JBS and GitHub All issues need to be files in JBS We have to write the issue number in the title of the pull request Additionally, comments to the pull request are send to related mailing lists of OpenJDK and vice versa
- Before creating a pull request, we have to sign OCA, that is Oracle Contribution Agreement For more information see this link
- Next, we create a pull request as usual This screenshot is my pull request
- We've submitting the patch Next step is receiving reviews
- Of course the pull request need to be reviewed The only people who has a reviewer role can review and approve the code Reviewer is one of the roles in OpenJDK Community
- I'll give a short explanation of roles in OpenJDK Everyone is a contributor at first They don't have any privileges After some contributions, you will be an Author I have this role I'll touch on what sponsoring means later At present, there are over three hundred committers and reviewers When you make many significant changes, you will become a committer or reviewer
- Let's get back to the pull request In this example, my pull request were reviewed by four reviewers
- This is the last step
- We can't merge our pull request by ourselves After the review, Reviewer or committer can sponsor the pull request The sponsor will merge it If you don’t have any role, your name will be recorded as a contributor
- In this screenshot, the sponsor run sponsor pull request command to merge this pull request
- We did it! I've explained all steps to fix a bug.
- Let me summarize Today I talked about contributing to OpenJDK There are many steps But don't be afraid You can do it Let's move OpenJDK forward together!
- I guess that's all I wanted to say today Thank you for your attention Enjoy this conference!