When running the following Java program:

public class Test {
        public static void main(String[] args) throws Exception {
                new java.text.SimpleDateFormat();
        }
}

with the JMC agent (https://github.com/openjdk/jmc/tree/master/agent) on a debug VM, the VM runs into an assertion:

# Internal Error (/usr/work/d039344/git/github.com/openjdk/jdk/src/hotspot/share/oops/instanceKlass.cpp:394), pid=94447, tid=94448
# assert(this_key != nullptr) failed: sanity


The problem seems tp be that the check_shared_class_super_types() in systemDictonary.cpp:1140 returns false, since the
IntFunction interface of the proxy class resolves to:

java.util.function.IntFunction {0x00007f29a30bcba8}
 - instance size: 2
 - klass size: 65
 - access: public interface abstract
 - flags: rewritten
 - state: linked
 - name: 'java/util/function/IntFunction'
 - super: 'java/lang/Object'
 - sub:
 - nof implementors: 2
 - arrays: null
 - methods: Array<T>(0x00007f299e64ccc8)
 - method ordering: Array<T>(0x00007f29a2bdbd08)
 - default_methods: Array<T>(0x0000000000000000)
 - local interfaces: Array<T>(0x00007f29a26aae30)
 - trans. interfaces: Array<T>(0x00007f29a26aae30)
 - constants: constant pool [14] {0x00007f299e64cbf0} for 'java/util/function/IntFunction' cache=0x00007f299e64d0b0
 - class loader data: loader data: 0x00007f2a4421b0a0 of 'bootstrap'
 - source file: 'IntFunction.java'
 - class annotations: Array<T>(0x00007f299e64cd88)
 - class type annotations: Array<T>(0x0000000000000000)
 - field annotations: Array<T>(0x0000000000000000)
 - field type annotations: Array<T>(0x0000000000000000)
 - generic signature: '<R:Ljava/lang/Object;>Ljava/lang/Object;'
 - inner classes: Array<T>(0x00007f29a26aadb8)
 - nest members: Array<T>(0x00007f29a26aadb8)
 - permitted subclasses: Array<T>(0x00007f29a26aadb8)
 - java mirror: a 'java/lang/Class'{0x000000011e2537c0} = 'java/util/function/IntFunction'
 - vtable length 5 (start addr: 0x00007f29a30bcd80)
 - itable length 0 (start addr: 0x00007f29a30bcda8)
 - ---- static fields (0 words):
 - ---- non-static fields (0 words):
 - non-static oop maps:
 
instead of
 
java.util.function.IntFunction {0x00007f29a217e760}
 - instance size: 2
 - klass size: 65
 - access: public interface abstract
 - flags: rewritten is_shared_boot_class
 - state: allocated
 - name: 'java/util/function/IntFunction'
 - super: 'java/lang/Object'
 - sub:
 - nof implementors: 0
 - arrays: null
 - methods: Array<T>(0x00007f29a28de5b8)
 - method ordering: Array<T>(0x00007f29a28de608)
 - default_methods: Array<T>(0x0000000000000000)
 - local interfaces: Array<T>(0x00007f29a26aae30)
 - trans. interfaces: Array<T>(0x00007f29a26aae30)
 - constants: constant pool [14] {0x00007f29a28de4f8} for 'java/util/function/IntFunction' cache=0x00007f29a217e980
 - source file: 'IntFunction.java'
 - class annotations: Array<T>(0x00007f29a28de4e8)
 - class type annotations: Array<T>(0x0000000000000000)
 - field annotations: Array<T>(0x0000000000000000)
 - field type annotations: Array<T>(0x0000000000000000)
 - generic signature: '<R:Ljava/lang/Object;>Ljava/lang/Object;'
 - inner classes: Array<T>(0x00007f29a26aadb8)
 - nest members: Array<T>(0x00007f29a26aadb8)
 - permitted subclasses: Array<T>(0x00007f29a26aadb8)
 - java mirror: null
 - vtable length 5 (start addr: 0x00007f29a217e938)
 - itable length 0 (start addr: 0x00007f29a217e960)
 - ---- static fields (0 words):
 - ---- non-static fields (0 words):
 - non-static oop maps:


Here is the lambda class:

sun.util.locale.provider.LocaleProviderAdapter$$Lambda/0x80000006e {0x00007f29a2387858}
 - instance size: 2
 - klass size: 69
 - access: final synchronized synthetic
 - flags: rewritten should_verify_class is_shared_boot_class has_vanilla_constructor
 - state: allocated
 - name: 'sun/util/locale/provider/LocaleProviderAdapter$$Lambda+0x80000006e'
 - super: 'java/lang/Object'
 - sub:
 - arrays: null
 - methods: Array<T>(0x00007f29a2bdb300)
 - method ordering: Array<T>(0x00007f29a2bdb398)
 - default_methods: Array<T>(0x0000000000000000)
 - local interfaces: Array<T>(0x00007f29a2bdb1f8)
 - trans. interfaces: Array<T>(0x00007f29a2bdb1f8)
 - constants: constant pool [21] {0x00007f29a2bdb208} for 'sun/util/locale/provider/LocaleProviderAdapter$$Lambda+0x80000006e' cache=0x00007f29a2387aa0
 - class annotations: Array<T>(0x0000000000000000)
 - class type annotations: Array<T>(0x0000000000000000)
 - field annotations: Array<T>(0x0000000000000000)
 - field type annotations: Array<T>(0x0000000000000000)
 - inner classes: Array<T>(0x00007f29a26aadb8)
 - nest members: Array<T>(0x00007f29a26aadb8)
 - permitted subclasses: Array<T>(0x00007f29a26aadb8)
 - java mirror: null
 - vtable length 5 (start addr: 0x00007f29a2387a30)
 - itable length 5 (start addr: 0x00007f29a2387a58)
 - ---- static fields (0 words):
 - ---- non-static fields (0 words):
 - non-static oop maps:

Because of this the class loader data is never set for the proxy in SystemDictionary::load_shared_lambda_proxy_class() and the assertion triggers.

Best regards,
Ralf