In hotspot/share/prims/jvmtiExport.cpp, method JvmtiExport::post_class_unload:

We have this code:

assert(thread->is_VM_thread(), "wrong thread");

// get JavaThread for whom we are proxy
Thread *calling_thread = ((VMThread *)thread)>vm_operation()>calling_thread();
if (!calling_thread->is_Java_thread())

{ // cannot post an event to a non-JavaThread return; }

 

It seems problematic if we would try to post outside a safepoint.