--- /dev/null	2020-01-17 11:46:19.065201212 +0100
+++ new/src/hotspot/share/gc/shared/parallelCleaning.cpp	2020-01-17 17:09:34.084132464 +0100
@@ -0,0 +1,331 @@
+/*
+ * Copyright (c) 2015, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "classfile/symbolTable.hpp"
+#include "classfile/stringTable.hpp"
+#include "code/codeCache.hpp"
+#include "gc/shared/parallelCleaning.hpp"
+#include "memory/resourceArea.hpp"
+#include "prims/resolvedMethodTable.hpp"
+#include "logging/log.hpp"
+#include "gc/shared/gcCause.hpp"
+#include "gc/shared/gcTraceTime.hpp"
+#include "gc/shared/gcTraceTime.inline.hpp"
+
+StringSymbolTableUnlinkTask::StringSymbolTableUnlinkTask(BoolObjectClosure* is_alive, bool process_strings, bool process_symbols) :
+  AbstractGangTask("String/Symbol Unlinking"),
+  _is_alive(is_alive),
+  _par_state_string(StringTable::weak_storage()),
+  _process_strings(process_strings), _strings_processed(0), _strings_removed(0),
+  _process_symbols(process_symbols), _symbols_processed(0), _symbols_removed(0) {
+
+  _initial_string_table_size = (int) StringTable::the_table()->table_size();
+  _initial_symbol_table_size = SymbolTable::the_table()->table_size();
+  if (process_symbols) {
+    SymbolTable::clear_parallel_claimed_index();
+  }
+}
+
+StringSymbolTableUnlinkTask::~StringSymbolTableUnlinkTask() {
+  guarantee(!_process_symbols || SymbolTable::parallel_claimed_index() >= _initial_symbol_table_size,
+            "claim value %d after unlink less than initial symbol table size %d",
+            SymbolTable::parallel_claimed_index(), _initial_symbol_table_size);
+
+  log_info(gc, stringtable)(
+      "Cleaned string and symbol table, "
+      "strings: " SIZE_FORMAT " processed, " SIZE_FORMAT " removed, "
+      "symbols: " SIZE_FORMAT " processed, " SIZE_FORMAT " removed",
+      strings_processed(), strings_removed(),
+      symbols_processed(), symbols_removed());
+}
+
+void StringSymbolTableUnlinkTask::work(uint worker_id) {
+  int strings_processed = 0;
+  int strings_removed = 0;
+  int symbols_processed = 0;
+  int symbols_removed = 0;
+  if (_process_strings) {
+    StringTable::possibly_parallel_unlink(&_par_state_string, _is_alive, &strings_processed, &strings_removed);
+    Atomic::add(strings_processed, &_strings_processed);
+    Atomic::add(strings_removed, &_strings_removed);
+  }
+  if (_process_symbols) {
+    SymbolTable::possibly_parallel_unlink(&symbols_processed, &symbols_removed);
+    Atomic::add(symbols_processed, &_symbols_processed);
+    Atomic::add(symbols_removed, &_symbols_removed);
+  }
+}
+
+size_t StringSymbolTableUnlinkTask::strings_processed() const { return (size_t)_strings_processed; }
+size_t StringSymbolTableUnlinkTask::strings_removed()   const { return (size_t)_strings_removed; }
+
+size_t StringSymbolTableUnlinkTask::symbols_processed() const { return (size_t)_symbols_processed; }
+size_t StringSymbolTableUnlinkTask::symbols_removed()   const { return (size_t)_symbols_removed; }
+
+
+Monitor* CodeCacheUnloadingTask::_lock = new Monitor(Mutex::leaf, "Code Cache Unload lock", false, Monitor::_safepoint_check_never);
+
+CodeCacheUnloadingTask::CodeCacheUnloadingTask(uint num_workers, BoolObjectClosure* is_alive, bool unloading_occurred) :
+  _is_alive(is_alive),
+  _unloading_occurred(unloading_occurred),
+  _num_workers(num_workers),
+  _first_nmethod(NULL),
+  _claimed_nmethod(NULL),
+  _postponed_list(NULL),
+  _num_entered_barrier(0)
+{
+  CompiledMethod::increase_unloading_clock();
+  // Get first alive nmethod
+  CompiledMethodIterator iter = CompiledMethodIterator();
+  if(iter.next_alive()) {
+    _first_nmethod = iter.method();
+  }
+  _claimed_nmethod = (volatile CompiledMethod*)_first_nmethod;
+}
+
+CodeCacheUnloadingTask::~CodeCacheUnloadingTask() {
+  CodeCache::verify_clean_inline_caches();
+
+  CodeCache::set_needs_cache_clean(false);
+  guarantee(CodeCache::scavenge_root_nmethods() == NULL, "Must be");
+
+  CodeCache::verify_icholder_relocations();
+}
+
+void CodeCacheUnloadingTask::add_to_postponed_list(CompiledMethod* nm) {
+  CompiledMethod* old;
+  do {
+    old = (CompiledMethod*)_postponed_list;
+    nm->set_unloading_next(old);
+  } while ((CompiledMethod*)Atomic::cmpxchg(nm, &_postponed_list, old) != old);
+}
+
+void CodeCacheUnloadingTask::clean_nmethod(CompiledMethod* nm) {
+  bool postponed = nm->do_unloading_parallel(_is_alive, _unloading_occurred);
+
+  if (postponed) {
+    // This nmethod referred to an nmethod that has not been cleaned/unloaded yet.
+    add_to_postponed_list(nm);
+  }
+
+  // Mark that this thread has been cleaned/unloaded.
+  // After this call, it will be safe to ask if this nmethod was unloaded or not.
+  nm->set_unloading_clock(CompiledMethod::global_unloading_clock());
+}
+
+void CodeCacheUnloadingTask::clean_nmethod_postponed(CompiledMethod* nm) {
+  nm->do_unloading_parallel_postponed();
+}
+
+void CodeCacheUnloadingTask::claim_nmethods(CompiledMethod** claimed_nmethods, int *num_claimed_nmethods) {
+  CompiledMethod* first;
+  CompiledMethodIterator last;
+
+  do {
+    *num_claimed_nmethods = 0;
+
+    first = (CompiledMethod*)_claimed_nmethod;
+    last = CompiledMethodIterator(first);
+
+    if (first != NULL) {
+
+      for (int i = 0; i < MaxClaimNmethods; i++) {
+        if (!last.next_alive()) {
+          break;
+        }
+        claimed_nmethods[i] = last.method();
+        (*num_claimed_nmethods)++;
+      }
+    }
+
+  } while ((CompiledMethod*)Atomic::cmpxchg(last.method(), &_claimed_nmethod, first) != first);
+}
+
+CompiledMethod* CodeCacheUnloadingTask::claim_postponed_nmethod() {
+  CompiledMethod* claim;
+  CompiledMethod* next;
+
+  do {
+    claim = (CompiledMethod*)_postponed_list;
+    if (claim == NULL) {
+      return NULL;
+    }
+
+    next = claim->unloading_next();
+
+  } while ((CompiledMethod*)Atomic::cmpxchg(next, &_postponed_list, claim) != claim);
+
+  return claim;
+}
+
+// Mark that we're done with the first pass of nmethod cleaning.
+void CodeCacheUnloadingTask::barrier_mark(uint worker_id) {
+  MonitorLockerEx ml(_lock, Mutex::_no_safepoint_check_flag);
+  _num_entered_barrier++;
+  if (_num_entered_barrier == _num_workers) {
+    ml.notify_all();
+  }
+}
+
+// See if we have to wait for the other workers to
+// finish their first-pass nmethod cleaning work.
+void CodeCacheUnloadingTask::barrier_wait(uint worker_id) {
+  if (_num_entered_barrier < _num_workers) {
+    MonitorLockerEx ml(_lock, Mutex::_no_safepoint_check_flag);
+    while (_num_entered_barrier < _num_workers) {
+      ml.wait(Mutex::_no_safepoint_check_flag, 0, false);
+    }
+  }
+}
+
+// Cleaning and unloading of nmethods. Some work has to be postponed
+// to the second pass, when we know which nmethods survive.
+void CodeCacheUnloadingTask::work_first_pass(uint worker_id) {
+  // The first nmethods is claimed by the first worker.
+  if (worker_id == 0 && _first_nmethod != NULL) {
+    clean_nmethod(_first_nmethod);
+    _first_nmethod = NULL;
+  }
+
+  int num_claimed_nmethods;
+  CompiledMethod* claimed_nmethods[MaxClaimNmethods];
+
+  while (true) {
+    claim_nmethods(claimed_nmethods, &num_claimed_nmethods);
+
+    if (num_claimed_nmethods == 0) {
+      break;
+    }
+
+    for (int i = 0; i < num_claimed_nmethods; i++) {
+      clean_nmethod(claimed_nmethods[i]);
+    }
+  }
+}
+
+void CodeCacheUnloadingTask::work_second_pass(uint worker_id) {
+  CompiledMethod* nm;
+  // Take care of postponed nmethods.
+  while ((nm = claim_postponed_nmethod()) != NULL) {
+    clean_nmethod_postponed(nm);
+  }
+}
+
+KlassCleaningTask::KlassCleaningTask(BoolObjectClosure* is_alive) :
+  _is_alive(is_alive),
+  _clean_klass_tree_claimed(0),
+  _klass_iterator() {
+}
+
+bool KlassCleaningTask::claim_clean_klass_tree_task() {
+  if (_clean_klass_tree_claimed) {
+    return false;
+  }
+
+  return Atomic::cmpxchg(1, &_clean_klass_tree_claimed, 0) == 0;
+}
+
+InstanceKlass* KlassCleaningTask::claim_next_klass() {
+  Klass* klass;
+  do {
+    klass =_klass_iterator.next_klass();
+  } while (klass != NULL && !klass->is_instance_klass());
+
+  // this can be null so don't call InstanceKlass::cast
+  return static_cast<InstanceKlass*>(klass);
+}
+
+void KlassCleaningTask::clean_klass(InstanceKlass* ik) {
+  ik->clean_weak_instanceklass_links();
+}
+
+void KlassCleaningTask::work() {
+  ResourceMark rm;
+
+  // One worker will clean the subklass/sibling klass tree.
+  if (claim_clean_klass_tree_task()) {
+    Klass::clean_subklass_tree();
+  }
+
+  // All workers will help cleaning the classes,
+  InstanceKlass* klass;
+  while ((klass = claim_next_klass()) != NULL) {
+    clean_klass(klass);
+  }
+}
+
+bool ResolvedMethodCleaningTask::claim_resolved_method_task() {
+  if (_resolved_method_task_claimed) {
+    return false;
+  }
+  return Atomic::cmpxchg(1, &_resolved_method_task_claimed, 0) == 0;
+}
+
+// These aren't big, one thread can do it all.
+void ResolvedMethodCleaningTask::work() {
+  if (claim_resolved_method_task()) {
+    ResolvedMethodTable::unlink();
+  }
+}
+
+ParallelCleaningTask::ParallelCleaningTask(BoolObjectClosure* is_alive,
+                                           bool process_strings,
+                                           bool process_symbols,
+                                           uint num_workers,
+                                           bool unloading_occurred) :
+  AbstractGangTask("Parallel Cleaning"),
+  _string_symbol_task(is_alive, process_strings, process_symbols),
+  _code_cache_task(num_workers, is_alive, unloading_occurred),
+  _klass_cleaning_task(is_alive),
+  _resolved_method_cleaning_task(is_alive)
+{
+
+
+}
+
+// The parallel work done by all worker threads.
+void ParallelCleaningTask::work(uint worker_id) {
+  // Do first pass of code cache cleaning.
+  _code_cache_task.work_first_pass(worker_id);
+
+  // Let the threads mark that the first pass is done.
+  _code_cache_task.barrier_mark(worker_id);
+
+  // Clean the Strings and Symbols.
+  _string_symbol_task.work(worker_id);
+
+  // Clean unreferenced things in the ResolvedMethodTable
+  _resolved_method_cleaning_task.work();
+
+  // Wait for all workers to finish the first code cache cleaning pass.
+  _code_cache_task.barrier_wait(worker_id);
+
+  // Do the second code cache cleaning work, which realize on
+  // the liveness information gathered during the first pass.
+  _code_cache_task.work_second_pass(worker_id);
+
+  // Clean all klasses that were not unloaded.
+  _klass_cleaning_task.work();
+}