8324680: Replace NULL with nullptr in JVMTI generated code

[sspitsyn]

This enhancement replaces uses of NULL with nullptr in the XML-description files for JVMTI. These are the files hotsport/share/prims/jvmti.xml and hotspot/share/prims/jvmti*.xls.

The following files are auto-generated from the jvmti.xml and *.xsl files in the build/<CFG>/variant-server/gensrc/jvmtifiles': jvmti.h, jvmti.html, jvmtiEnter.cpp, jvmtiEnterTrace.cpp, jvmtiEnv.hpp`

This addresses a category of NULL uses that wasn't dealt with by:
JDK-8299837.

Testing:

• TBD: run mach5 tiers1-3

---

Progress

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Issue

• JDK-8324680: Replace NULL with nullptr in JVMTI generated code (Enhancement - P4)

Reviewers

• Alex Menkov (@alexmenkov - Reviewer)
• Coleen Phillimore (@coleenp - Reviewer)

Reviewing

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[openjdk]

@sspitsyn This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8324680: Replace NULL with nullptr in JVMTI generated code

Reviewed-by: amenkov, coleenp

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At the time when this comment was updated there had been 59 new commits pushed to the master branch:

• 0aaec97: 8325763: Revert properties: vm.opt.x.*
• 4018b2b: 8323782: Race: Thread::interrupt vs. AbstractInterruptibleChannel.begin
• 2705ed0: 8325074: ZGC fails assert(index == 0 || is_power_of_2(index)) failed: Incorrect load shift: 11
• 3d85103: 8316813: NMT: Using WhiteBox API, virtual memory tracking should also be stressed in JMH tests
• ba8db1f: 8325876: crashes in docker container tests on Linuxppc64le Power8 machines
• 18cea82: 8319801: Recursive lightweight locking: aarch64 implementation
• 9029bf6: 8316451: 6 java/lang/instrument/PremainClass tests ignore VM flags
• 99c9ae1: 8323664: java/awt/font/JNICheck/FreeTypeScalerJNICheck.java still fails with JNI warning on some Windows configurations
• 0fdfdf7: 8325983: Build failure after JDK-8324580
• 3b1062d: 8322239: [macos] a11y : java.lang.NullPointerException is thrown when focus is moved on the JTabbedPane
• ... and 49 more: https://git.openjdk.org/jdk/compare/b356fee5d82c3c72a705bb33b73189921a813828...master

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[sspitsyn]

Thank you for review, Alex!

[coleenp]

Looks good, thanks for fixing this.

[sspitsyn]

Thank you for review, Coleen!

[sspitsyn]

/integrate

[openjdk]

Going to push as commit 267780b.
Since your change was applied there have been 68 commits pushed to the master branch:

• f3073db: 8321408: Add Certainly roots R1 and E1
• 4c7b313: 8325908: Finish removal of IntlTest and CollatorTest
• 5310250: 8325941: Remove unused Space::block_size
• 7a76252: 8325990: Remove use of snippet @replace annotation in java.base
• 00b5c70: 8326062: ProblemList jcstress tests that are failing due to JDK-8325984
• 4388095: 8325326: [PPC64] Don't relocate in case of allocation failure
• 244573e: 8265372: Simplify PKCS9Attribute
• 80b63b6: 8323801: tag doesn't strikethrough the text
• 9f4ec21: 8325862: set -XX:+ErrorFileToStderr when executing java in containers for some container related jtreg tests
• 0aaec97: 8325763: Revert properties: vm.opt.x.*
• ... and 58 more: https://git.openjdk.org/jdk/compare/b356fee5d82c3c72a705bb33b73189921a813828...master

Your commit was automatically rebased without conflicts.

[openjdk]

@sspitsyn Pushed as commit 267780b.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

[AlanBateman]

JVMTI agents can be developed in C or C++. If I read this changes correctly, then this will replace all the NULLs in the generated spec with nullptr. I wonder if this needs some setup in the Introduction section, e.g. the Function Return Values subsection, to make this clear.

[dholmes-ora]

As with the other NULL -> nullptr changes, when it involves text (as opposed to code) and we are discussing the general concept of nullness, then the word "null" should be used rather than the programmatic values NULL or nullptr. But if the source here is used to generated both the spec's functional descriptions and the code functions themselves, then we cannot make that distinction. I'm not sure this change was actually a good idea. At a minimum we need something like @AlanBateman suggests, something upfront to say that where the spec says nullptr it also means a C null pointer.

[sspitsyn]

Now, we this section:

Function Return Values

JVM TI functions always return an error code via the jvmtiError function return value. Some functions can return additional values through pointers provided by the calling function. In some cases, JVM TI functions allocate memory that your program must explicitly deallocate. This is indicated in the individual JVM TI function descriptions. Empty lists, arrays, sequences, etc are returned as nullptr.
In the event that the JVM TI function encounters an error (any return value other than JVMTI_ERROR_NONE) the values of memory referenced by argument pointers is undefined, but no memory will have been allocated and no global references will have been allocated. If the error occurs because of invalid input, no action will have occurred.

The nullptr is mentioned here. As I understand from the Alan's and David's comments above we want to clarify what does it mean for C/C++ code.

[sspitsyn]

Filed new Enhancement:
8326716: JVMTI spec: clarify what nullptr means for C/C++ developers