Enable live heap profiling by default on safe JVM versions

[jbachorik]

What Does This Do

Adds a unified config key profiling.liveheap.enabled that auto-detects safe systems and enables live heap profiling by default. The ddprof native library is preferred, with JFR jdk.OldObjectSample as an automatic fallback.

Introduces profiling.jfr.liveheap.enabled as the replacement for the deprecated profiling.heap.enabled, with context-aware deprecation warnings. Cross-awareness between ddprof and JFR paths prevents double collection and warns when live heap profiling becomes effectively inactive.

Enablement Logic

flowchart TD
    A["profiling.liveheap.enabled\n(unified master switch)"]
    A -->|"false"| B["ALL live heap OFF\n(ddprof + JFR)"]
    A -->|"unset or true"| C{Split into two paths}

    C --> D["ddprof path\nDatadogProfilerConfig"]
    C --> E["JFR path\nOpenJdkController"]

    D --> JFRCHK{"profiling.jfr.liveheap.enabled\nexplicitly true?"}
    JFRCHK -->|yes| JFRDIS["ddprof MEMLEAK OFF\n⚠️ warn: JFR explicitly requested,\ndisabling ddprof (superior mode)\nto avoid double collection"]
    JFRCHK -->|no| F["profiling.ddprof.liveheap.enabled"]
    F -->|"false"| G["MEMLEAK OFF"]
    F -->|"unset or true"\ndefault = isJmethodIDSafe| H{"JVM safe?\nJava 8, 11.0.23+,\n17.0.11+, 21.0.3+, 22+"}
    H -->|yes| I[MEMLEAK ON]
    H -->|no| J["MEMLEAK ON\n⚠️ warn: not stable on this JVM"]

    G --> GCHK{"JFR OldObjectSample\navailable?"}
    GCHK -->|no| GWARN["⚠️ warn: live heap\nwill be inactive"]
    GCHK -->|yes| GOK[JFR fallback active]

    E --> K{"Which key is set?"}
    K -->|"profiling.jfr.liveheap.enabled"| L{value?}
    K -->|"profiling.heap.enabled\n(deprecated)"| DEP{ddprof likely active?}
    K -->|"neither set"| NOKEY{"ddprof likely\nactive?"}

    L -->|"true"| L1[OldObjectSample ON]
    L -->|"false"| LCHK{"ddprof likely\nactive?"}
    LCHK -->|yes| L2[OldObjectSample OFF]
    LCHK -->|no| L2WARN["OldObjectSample OFF\n⚠️ warn: live heap\nwill be inactive"]

    NOKEY -->|yes| NOKEY_OFF["OldObjectSample OFF\n(ddprof handles live heap)"]
    NOKEY -->|no| NOKEY_JFP{"JVM supports it?\nJava 11.0.12+,\n17.0.3+, 18+"}
    NOKEY_JFP -->|yes| O["OldObjectSample ON\n(JFR fallback)"]
    NOKEY_JFP -->|no| P[OldObjectSample OFF]

    DEP -->|yes| DEP1["⚠️ warn: has no effect\n(ddprof handles live heap)\nkey ignored"]
    DEP -->|"no, value=true"| DEP2["⚠️ warn: redundant\n(JFR already on by default)"]
    DEP -->|"no, value=false"| DEP3["⚠️ warn: use new key\nprofiling.jfr.liveheap.enabled"]
    DEP2 --> DEP_ON[OldObjectSample ON]
    DEP3 --> DEP_OFF[OldObjectSample OFF]

    style B fill:#f66,color:#fff
    style G fill:#f66,color:#fff
    style JFRDIS fill:#fa0,color:#fff
    style L2 fill:#f66,color:#fff
    style L2WARN fill:#f66,color:#fff
    style NOKEY_OFF fill:#69c,color:#fff
    style P fill:#f66,color:#fff
    style DEP_OFF fill:#f66,color:#fff
    style GWARN fill:#fa0,color:#fff
    style I fill:#6b6,color:#fff
    style J fill:#fa0,color:#fff
    style L1 fill:#6b6,color:#fff
    style O fill:#6b6,color:#fff
    style GOK fill:#6b6,color:#fff
    style DEP_ON fill:#6b6,color:#fff
    style DEP1 fill:#fd6,color:#333
    style DEP2 fill:#fd6,color:#333
    style DEP3 fill:#fd6,color:#333

Loading

Note: When ddprof MEMLEAK is active, disableOverriddenEvents() at recording start also disables jdk.OldObjectSample as a safety net. The proactive disable in the constructor ensures the settings map is consistent from the start.

Motivation

Live heap profiling provides valuable memory leak detection but was previously opt-in (profiling.ddprof.liveheap.enabled defaulted to false). Users had to know about and explicitly enable it.

This change makes it enabled by default on safe systems, matching the pattern already used by allocation profiling. The two live heap mechanisms (ddprof native and JFR OldObjectSample) are now unified under a single flag with automatic fallback.

[PROF-14188]

Additional Notes

• isMemoryLeakProfilingSafe() returns true when at least one safe mechanism is available: isJmethodIDSafe() || isOldObjectSampleAvailable()
• The ddprof-specific key default changed from hardcoded false to dynamic isJmethodIDSafe()
• Cross-awareness between paths:
  • profiling.jfr.liveheap.enabled=true disables ddprof MEMLEAK on user request (avoids double collection)
  • profiling.ddprof.liveheap.enabled=false with no JFR fallback warns about inactive live heap
  • profiling.jfr.liveheap.enabled=false with no ddprof warns about inactive live heap
  • No explicit JFR key + ddprof active: OldObjectSample proactively disabled (no double collection)
• Deprecation warnings for profiling.heap.enabled are context-aware:
  • When ddprof handles live heap: "has no effect" (key ignored)
  • When JFR fallback, value=true: "redundant"
  • When JFR fallback, value=false: "use new key instead"
• Pre-existing bug fixed: isEventEnabled was called with jdk.OldObjectSample#enabled which resulted in a double #enabled lookup, making the warning dead code

Contributor Checklist

• Format the title according to the contribution guidelines
• Assign the type: and (comp: or inst:) labels in addition to any other useful labels
• Avoid using close, fix, or any linking keywords when referencing an issue
  Use solves instead, and assign the PR milestone to the issue
• Update the CODEOWNERS file on source file addition, migration, or deletion
• Update public documentation with any new configuration flags or behaviors

Jira ticket: [PROF-14188]

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