8207778: Add locking to ModuleEntry and PackageEntry tables

Restructure ClassLoaderDataGraph code to simplify using locks in SystemDictionary::do_unloading()

Reviewed-by: lfoltan, coleenp

src/hotspot/share/classfile/classLoaderData.cpp

@@ -1418,7 +1418,18 @@ bool ClassLoaderDataGraph::do_unloading(bool do_cleaning) {
   }
 
   if (seen_dead_loader) {
-    data = _head;
+    JFR_ONLY(post_class_unload_events();)
+  }
+
+  log_debug(class, loader, data)("do_unloading: loaders processed %u, loaders removed %u", loaders_processed, loaders_removed);
+
+  return seen_dead_loader;
+}
+
+// There's at least one dead class loader.  Purge refererences of healthy module
+// reads lists and package export lists to modules belonging to dead loaders.
+void ClassLoaderDataGraph::clean_module_and_package_info() {
+  ClassLoaderData* data = _head;
   while (data != NULL) {
     // Remove entries in the dictionary of live class loader that have
     // initiated loading classes in a dead class loader.
@@ -1439,12 +1450,6 @@ bool ClassLoaderDataGraph::do_unloading(bool do_cleaning) {
     }
     data = data->next();
   }
-    JFR_ONLY(post_class_unload_events();)
-  }
-
-  log_debug(class, loader, data)("do_unloading: loaders processed %u, loaders removed %u", loaders_processed, loaders_removed);
-
-  return seen_dead_loader;
 }
 
 void ClassLoaderDataGraph::purge() {

src/hotspot/share/classfile/classLoaderData.hpp

@@ -97,6 +97,7 @@ class ClassLoaderDataGraph : public AllStatic {
 
  public:
   static ClassLoaderData* find_or_create(Handle class_loader);
+  static void clean_module_and_package_info();
   static void purge();
   static void clear_claimed_marks();
   // oops do

src/hotspot/share/classfile/loaderConstraints.cpp

@@ -65,7 +65,7 @@ void LoaderConstraintTable::free_entry(LoaderConstraintEntry *entry) {
 
 LoaderConstraintEntry** LoaderConstraintTable::find_loader_constraint(
                                     Symbol* name, Handle loader) {
-
+  assert_lock_strong(SystemDictionary_lock);
   unsigned int hash = compute_hash(name);
   int index = hash_to_index(hash);
   LoaderConstraintEntry** pp = bucket_addr(index);
@@ -89,7 +89,7 @@ LoaderConstraintEntry** LoaderConstraintTable::find_loader_constraint(
 
 
 void LoaderConstraintTable::purge_loader_constraints() {
-  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+  assert_locked_or_safepoint(SystemDictionary_lock);
   LogTarget(Info, class, loader, constraints) lt;
   // Remove unloaded entries from constraint table
   for (int index = 0; index < table_size(); index++) {

src/hotspot/share/classfile/moduleEntry.cpp

@@ -436,7 +436,7 @@ ModuleEntry* ModuleEntryTable::lookup_only(Symbol* name) {
 // Remove dead modules from all other alive modules' reads list.
 // This should only occur at class unloading.
 void ModuleEntryTable::purge_all_module_reads() {
-  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+  assert_locked_or_safepoint(Module_lock);
   for (int i = 0; i < table_size(); i++) {
     for (ModuleEntry* entry = bucket(i);
                       entry != NULL;

src/hotspot/share/classfile/packageEntry.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -302,7 +302,7 @@ bool PackageEntry::exported_pending_delete() const {
 
 // Remove dead entries from all packages' exported list
 void PackageEntryTable::purge_all_package_exports() {
-  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+  assert_locked_or_safepoint(Module_lock);
   for (int i = 0; i < table_size(); i++) {
     for (PackageEntry* entry = bucket(i);
                        entry != NULL;

src/hotspot/share/classfile/resolutionErrors.cpp

@@ -100,7 +100,7 @@ ResolutionErrorTable::ResolutionErrorTable(int table_size)
 // RedefineClasses support - remove matching entry of a
 // constant pool that is going away
 void ResolutionErrorTable::delete_entry(ConstantPool* c) {
-  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+  assert_locked_or_safepoint(SystemDictionary_lock);
   for (int i = 0; i < table_size(); i++) {
     for (ResolutionErrorEntry** p = bucket_addr(i); *p != NULL; ) {
       ResolutionErrorEntry* entry = *p;
@@ -118,7 +118,7 @@ void ResolutionErrorTable::delete_entry(ConstantPool* c) {
 
 // Remove unloaded entries from the table
 void ResolutionErrorTable::purge_resolution_errors() {
-  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+  assert_locked_or_safepoint(SystemDictionary_lock);
   for (int i = 0; i < table_size(); i++) {
     for (ResolutionErrorEntry** p = bucket_addr(i); *p != NULL; ) {
       ResolutionErrorEntry* entry = *p;

src/hotspot/share/classfile/systemDictionary.cpp

@@ -1853,6 +1853,9 @@ bool SystemDictionary::do_unloading(GCTimer* gc_timer,
 
     // First, mark for unload all ClassLoaderData referencing a dead class loader.
     unloading_occurred = ClassLoaderDataGraph::do_unloading(do_cleaning);
+    if (unloading_occurred) {
+      ClassLoaderDataGraph::clean_module_and_package_info();
+    }
   }
 
   if (unloading_occurred) {