8373392: Replace CDS object subgraphs with @AOTSafeClassInitializer

[iklam]

In legacy CDS, Java objects used by certain classes are computed ahead of time using "object subgraphs"

jdk/src/hotspot/share/cds/heapShared.cpp

Lines 168 to 171 in 1bbbce7

	static ArchivableStaticFieldInfo archive_subgraph_entry_fields[] = {
	{"java/lang/Integer$IntegerCache", "archivedCache"},
	{"java/lang/Long$LongCache", "archivedCache"},
	{"java/lang/Byte$ByteCache", "archivedCache"},

Examples of subgraphs:

• java.lang.Integer$IntegerCache::cache
• jdk.internal.module.ArchivedBootLayer::bootLayer

The implementation requires special code (in both Java and C++) to be executed when a CDS archive is created or loaded. As a result, we have an execution model that's difficult to implement/extend and the behavior is hard to understand.

To move towards the AOT Cache Snapshot Model (JDK-8365645) we should replace the subgraphs with the use of @AOTSafeClassInitializer, and if necessary, @AOTRuntimeSetup. This will simplify the current implementation, and make it possible to extend AOT-initializations to more core classes.

Note, the use of @AOTSafeClassInitializer requires -XX:+AOTClassLinking. For the time being, we retain the old CDS object subgraph code to cover the -XX:-AOTClassLinking cases. Such code will be marked with comments like /* Legacy CDS archive support (to be deprecated) */. All future AOT creation of Java objects will be done with @AOTSafeClassInitializer.

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Issue

• JDK-8373392: Replace CDS object subgraphs with @AOTSafeClassInitializer (Enhancement - P4)

Reviewers

• Chen Liang (@liach - Reviewer)

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[openjdk]

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8373392: Replace CDS object subgraphs with @AOTSafeClassInitializer

Reviewed-by: liach

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At the time when this comment was updated there had been 6 new commits pushed to the master branch:

• 54430a8: 8373362: Http3TestServer should not log an exception stack trace when it is stopping normally
• 655e9cd: 8373335: Serial: Clean up SerialHeap members by access specifies
• b58e3b6: 8373227: Test java/net/httpclient/http2/StreamFlowControlTest.java failed: should sleep time be raised?
• ... and 3 more: https://git.openjdk.org/jdk/compare/1bbbce75c5e68429c2a32519eb3c36d964dcdf57...master

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[mlbridge]

Webrevs

• 00: Full (562d15a9)

[liach]

Is IntegerCache.cache the only field that need to be adjusted according to system properties after loading from AOT archive?

[liach]

Suggested change

	// to generate a reasonably random and well-mixed SALT, use an arbitrary
	// to generate a reasonably random and well-mixed SALT, use an arbitrary

[iklam]

Is IntegerCache.cache the only field that need to be adjusted according to system properties after loading from AOT archive?

I think so. The cache size for all other Number types are fixed and cannot be modified by the command-line.

[liach]

The Java code changes look reasonable.