src/hotspot/share/gc/g1/g1CollectedHeap.cpp
changeset 51488 d14d24d076b7
parent 51476 6c0ac4b4d761
child 51494 1906adbef2dc
--- a/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Sun Aug 19 20:00:57 2018 +0200
+++ b/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Wed Aug 22 16:01:29 2018 +0200
@@ -70,7 +70,6 @@
 #include "gc/shared/generationSpec.hpp"
 #include "gc/shared/isGCActiveMark.hpp"
 #include "gc/shared/oopStorageParState.hpp"
-#include "gc/shared/parallelCleaning.hpp"
 #include "gc/shared/preservedMarks.inline.hpp"
 #include "gc/shared/suspendibleThreadSet.hpp"
 #include "gc/shared/referenceProcessor.inline.hpp"
@@ -3255,12 +3254,334 @@
                undo_waste * HeapWordSize / K);
 }
 
+class G1StringCleaningTask : public AbstractGangTask {
+private:
+  BoolObjectClosure* _is_alive;
+  G1StringDedupUnlinkOrOopsDoClosure _dedup_closure;
+  OopStorage::ParState<false /* concurrent */, false /* const */> _par_state_string;
+
+  int _initial_string_table_size;
+
+  bool  _process_strings;
+  int _strings_processed;
+  int _strings_removed;
+
+  bool _process_string_dedup;
+
+public:
+  G1StringCleaningTask(BoolObjectClosure* is_alive, bool process_strings, bool process_string_dedup) :
+    AbstractGangTask("String Unlinking"),
+    _is_alive(is_alive),
+    _dedup_closure(is_alive, NULL, false),
+    _par_state_string(StringTable::weak_storage()),
+    _process_strings(process_strings), _strings_processed(0), _strings_removed(0),
+    _process_string_dedup(process_string_dedup) {
+
+    _initial_string_table_size = (int) StringTable::the_table()->table_size();
+    if (process_strings) {
+      StringTable::reset_dead_counter();
+    }
+  }
+
+  ~G1StringCleaningTask() {
+    log_info(gc, stringtable)(
+        "Cleaned string table, "
+        "strings: " SIZE_FORMAT " processed, " SIZE_FORMAT " removed",
+        strings_processed(), strings_removed());
+    if (_process_strings) {
+      StringTable::finish_dead_counter();
+    }
+  }
+
+  void work(uint worker_id) {
+    int strings_processed = 0;
+    int strings_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_string_dedup) {
+      G1StringDedup::parallel_unlink(&_dedup_closure, worker_id);
+    }
+  }
+
+  size_t strings_processed() const { return (size_t)_strings_processed; }
+  size_t strings_removed()   const { return (size_t)_strings_removed; }
+};
+
+class G1CodeCacheUnloadingTask {
+private:
+  static Monitor* _lock;
+
+  BoolObjectClosure* const _is_alive;
+  const bool               _unloading_occurred;
+  const uint               _num_workers;
+
+  // Variables used to claim nmethods.
+  CompiledMethod* _first_nmethod;
+  CompiledMethod* volatile _claimed_nmethod;
+
+  // The list of nmethods that need to be processed by the second pass.
+  CompiledMethod* volatile _postponed_list;
+  volatile uint            _num_entered_barrier;
+
+ public:
+  G1CodeCacheUnloadingTask(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 = _first_nmethod;
+  }
+
+  ~G1CodeCacheUnloadingTask() {
+    CodeCache::verify_clean_inline_caches();
+
+    CodeCache::set_needs_cache_clean(false);
+    guarantee(CodeCache::scavenge_root_nmethods() == NULL, "Must be");
+
+    CodeCache::verify_icholder_relocations();
+  }
+
+ private:
+  void add_to_postponed_list(CompiledMethod* nm) {
+      CompiledMethod* old;
+      do {
+        old = _postponed_list;
+        nm->set_unloading_next(old);
+      } while (Atomic::cmpxchg(nm, &_postponed_list, old) != old);
+  }
+
+  void 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 nmethod 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 clean_nmethod_postponed(CompiledMethod* nm) {
+    nm->do_unloading_parallel_postponed();
+  }
+
+  static const int MaxClaimNmethods = 16;
+
+  void claim_nmethods(CompiledMethod** claimed_nmethods, int *num_claimed_nmethods) {
+    CompiledMethod* first;
+    CompiledMethodIterator last;
+
+    do {
+      *num_claimed_nmethods = 0;
+
+      first = _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 (Atomic::cmpxchg(last.method(), &_claimed_nmethod, first) != first);
+  }
+
+  CompiledMethod* claim_postponed_nmethod() {
+    CompiledMethod* claim;
+    CompiledMethod* next;
+
+    do {
+      claim = _postponed_list;
+      if (claim == NULL) {
+        return NULL;
+      }
+
+      next = claim->unloading_next();
+
+    } while (Atomic::cmpxchg(next, &_postponed_list, claim) != claim);
+
+    return claim;
+  }
+
+ public:
+  // Mark that we're done with the first pass of nmethod cleaning.
+  void 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 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 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 work_second_pass(uint worker_id) {
+    CompiledMethod* nm;
+    // Take care of postponed nmethods.
+    while ((nm = claim_postponed_nmethod()) != NULL) {
+      clean_nmethod_postponed(nm);
+    }
+  }
+};
+
+Monitor* G1CodeCacheUnloadingTask::_lock = new Monitor(Mutex::leaf, "Code Cache Unload lock", false, Monitor::_safepoint_check_never);
+
+class G1KlassCleaningTask : public StackObj {
+  volatile int                            _clean_klass_tree_claimed;
+  ClassLoaderDataGraphKlassIteratorAtomic _klass_iterator;
+
+ public:
+  G1KlassCleaningTask() :
+      _clean_klass_tree_claimed(0),
+      _klass_iterator() {
+  }
+
+ private:
+  bool claim_clean_klass_tree_task() {
+    if (_clean_klass_tree_claimed) {
+      return false;
+    }
+
+    return Atomic::cmpxchg(1, &_clean_klass_tree_claimed, 0) == 0;
+  }
+
+  InstanceKlass* 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);
+  }
+
+public:
+
+  void clean_klass(InstanceKlass* ik) {
+    ik->clean_weak_instanceklass_links();
+  }
+
+  void 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);
+    }
+  }
+};
+
+// To minimize the remark pause times, the tasks below are done in parallel.
+class G1ParallelCleaningTask : public AbstractGangTask {
+private:
+  bool                          _unloading_occurred;
+  G1StringCleaningTask          _string_task;
+  G1CodeCacheUnloadingTask      _code_cache_task;
+  G1KlassCleaningTask           _klass_cleaning_task;
+
+public:
+  // The constructor is run in the VMThread.
+  G1ParallelCleaningTask(BoolObjectClosure* is_alive, uint num_workers, bool unloading_occurred) :
+      AbstractGangTask("Parallel Cleaning"),
+      _unloading_occurred(unloading_occurred),
+      _string_task(is_alive, true, G1StringDedup::is_enabled()),
+      _code_cache_task(num_workers, is_alive, unloading_occurred),
+      _klass_cleaning_task() {
+  }
+
+  // The parallel work done by all worker threads.
+  void 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.
+    _string_task.work(worker_id);
+
+    // 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.
+    // The weak metadata in klass doesn't need to be
+    // processed if there was no unloading.
+    if (_unloading_occurred) {
+      _klass_cleaning_task.work();
+    }
+  }
+};
+
+
 void G1CollectedHeap::complete_cleaning(BoolObjectClosure* is_alive,
                                         bool class_unloading_occurred) {
   uint n_workers = workers()->active_workers();
 
-  G1StringDedupUnlinkOrOopsDoClosure dedup_closure(is_alive, NULL, false);
-  ParallelCleaningTask g1_unlink_task(is_alive, &dedup_closure, n_workers, class_unloading_occurred);
+  G1ParallelCleaningTask g1_unlink_task(is_alive, n_workers, class_unloading_occurred);
   workers()->run_task(&g1_unlink_task);
 }
 
@@ -3272,8 +3593,7 @@
     return;
   }
 
-  G1StringDedupUnlinkOrOopsDoClosure dedup_closure(is_alive, NULL, false);
-  StringCleaningTask g1_unlink_task(is_alive, process_string_dedup ? &dedup_closure : NULL, process_strings);
+  G1StringCleaningTask g1_unlink_task(is_alive, process_strings, process_string_dedup);
   workers()->run_task(&g1_unlink_task);
 }