1 /*

     2  * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  */

    23 

    24 #include "precompiled.hpp"

    25 #include "classfile/javaClasses.inline.hpp"

    26 #include "gc/shared/referencePolicy.hpp"

    27 #include "gc/shared/referenceProcessorStats.hpp"

    28 #include "gc/z/zHeap.inline.hpp"

    29 #include "gc/z/zOopClosures.inline.hpp"

    30 #include "gc/z/zReferenceProcessor.hpp"

    31 #include "gc/z/zStat.hpp"

    32 #include "gc/z/zTask.hpp"

    33 #include "gc/z/zTracer.inline.hpp"

    34 #include "gc/z/zUtils.inline.hpp"

    35 #include "memory/universe.hpp"

    36 #include "runtime/mutexLocker.hpp"

    37 #include "runtime/os.hpp"

    38 

    39 static const ZStatSubPhase ZSubPhaseConcurrentReferencesProcess("Concurrent References Process");

    40 static const ZStatSubPhase ZSubPhaseConcurrentReferencesEnqueue("Concurrent References Enqueue");

    41 

    42 ZReferenceProcessor::ZReferenceProcessor(ZWorkers* workers) :

    43     _workers(workers),

    44     _soft_reference_policy(NULL),

    45     _encountered_count(),

    46     _discovered_count(),

    47     _enqueued_count(),

    48     _discovered_list(NULL),

    49     _pending_list(NULL),

    50     _pending_list_tail(_pending_list.addr()) {}

    51 

    52 void ZReferenceProcessor::set_soft_reference_policy(bool clear) {

    53   static AlwaysClearPolicy always_clear_policy;

    54   static LRUMaxHeapPolicy lru_max_heap_policy;

    55 

    56   if (clear) {

    57     log_info(gc, ref)("Clearing All Soft References");

    58     _soft_reference_policy = &always_clear_policy;

    59   } else {

    60     _soft_reference_policy = &lru_max_heap_policy;

    61   }

    62 

    63   _soft_reference_policy->setup();

    64 }

    65 

    66 void ZReferenceProcessor::update_soft_reference_clock() const {

    67   const jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;

    68   java_lang_ref_SoftReference::set_clock(now);

    69 }

    70 

    71 bool ZReferenceProcessor::is_reference_inactive(oop obj) const {

    72   // A non-null next field means the reference is inactive

    73   return java_lang_ref_Reference::next(obj) != NULL;

    74 }

    75 

    76 ReferenceType ZReferenceProcessor::reference_type(oop obj) const {

    77   return InstanceKlass::cast(obj->klass())->reference_type();

    78 }

    79 

    80 const char* ZReferenceProcessor::reference_type_name(ReferenceType type) const {

    81   switch (type) {

    82   case REF_SOFT:

    83     return "Soft";

    84 

    85   case REF_WEAK:

    86     return "Weak";

    87 

    88   case REF_FINAL:

    89     return "Final";

    90 

    91   case REF_PHANTOM:

    92     return "Phantom";

    93 

    94   default:

    95     ShouldNotReachHere();

    96     return NULL;

    97   }

    98 }

    99 

   100 volatile oop* ZReferenceProcessor::reference_referent_addr(oop obj) const {

   101   return (volatile oop*)java_lang_ref_Reference::referent_addr_raw(obj);

   102 }

   103 

   104 oop ZReferenceProcessor::reference_referent(oop obj) const {

   105   return *reference_referent_addr(obj);

   106 }

   107 

   108 bool ZReferenceProcessor::is_referent_alive_or_null(oop obj, ReferenceType type) const {

   109   volatile oop* const p = reference_referent_addr(obj);

   110 

   111   // Check if the referent is alive or null, in which case we don't want to discover

   112   // the reference. It can only be null if the application called Reference.enqueue()

   113   // or Reference.clear().

   114   if (type == REF_PHANTOM) {

   115     const oop o = ZBarrier::weak_load_barrier_on_phantom_oop_field(p);

   116     return o == NULL || ZHeap::heap()->is_object_live(ZOop::to_address(o));

   117   } else {

   118     const oop o = ZBarrier::weak_load_barrier_on_weak_oop_field(p);

   119     return o == NULL || ZHeap::heap()->is_object_strongly_live(ZOop::to_address(o));

   120   }

   121 }

   122 

   123 bool ZReferenceProcessor::is_referent_softly_alive(oop obj, ReferenceType type) const {

   124   if (type != REF_SOFT) {

   125     // Not a soft reference

   126     return false;

   127   }

   128 

   129   // Ask soft reference policy

   130   const jlong clock = java_lang_ref_SoftReference::clock();

   131   assert(clock != 0, "Clock not initialized");

   132   assert(_soft_reference_policy != NULL, "Policy not initialized");

   133   return !_soft_reference_policy->should_clear_reference(obj, clock);

   134 }

   135 

   136 bool ZReferenceProcessor::should_drop_reference(oop obj, ReferenceType type) const {

   137   // This check is racing with a call to Reference.clear() from the application.

   138   // If the application clears the reference after this check it will still end

   139   // up on the pending list, and there's nothing we can do about that without

   140   // changing the Reference.clear() API. This check is also racing with a call

   141   // to Reference.enqueue() from the application, which is unproblematic, since

   142   // the application wants the reference to be enqueued anyway.

   143   const oop o = reference_referent(obj);

   144   if (o == NULL) {

   145     // Reference has been cleared, by a call to Reference.enqueue()

   146     // or Reference.clear() from the application, which means we

   147     // should drop the reference.

   148     return true;

   149   }

   150 

   151   // Check if the referent is still alive, in which case we should

   152   // drop the reference.

   153   if (type == REF_PHANTOM) {

   154     return ZBarrier::is_alive_barrier_on_phantom_oop(o);

   155   } else {

   156     return ZBarrier::is_alive_barrier_on_weak_oop(o);

   157   }

   158 }

   159 

   160 bool ZReferenceProcessor::should_mark_referent(ReferenceType type) const {

   161   // Referents of final references (and its reachable sub graph) are

   162   // always marked finalizable during discovery. This avoids the problem

   163   // of later having to mark those objects if the referent is still final

   164   // reachable during processing.

   165   return type == REF_FINAL;

   166 }

   167 

   168 bool ZReferenceProcessor::should_clear_referent(ReferenceType type) const {

   169   // Referents that were not marked must be cleared

   170   return !should_mark_referent(type);

   171 }

   172 

   173 void ZReferenceProcessor::keep_referent_alive(oop obj, ReferenceType type) const {

   174   volatile oop* const p = reference_referent_addr(obj);

   175   if (type == REF_PHANTOM) {

   176     ZBarrier::keep_alive_barrier_on_phantom_oop_field(p);

   177   } else {

   178     ZBarrier::keep_alive_barrier_on_weak_oop_field(p);

   179   }

   180 }

   181 

   182 bool ZReferenceProcessor::discover_reference(oop obj, ReferenceType type) {

   183   if (!RegisterReferences) {

   184     // Reference processing disabled

   185     return false;

   186   }

   187 

   188   log_trace(gc, ref)("Encountered Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));

   189 

   190   // Update statistics

   191   _encountered_count.get()[type]++;

   192 

   193   if (is_reference_inactive(obj) ||

   194       is_referent_alive_or_null(obj, type) ||

   195       is_referent_softly_alive(obj, type)) {

   196     // Not discovered

   197     return false;

   198   }

   199 

   200   discover(obj, type);

   201 

   202   // Discovered

   203   return true;

   204 }

   205 

   206 void ZReferenceProcessor::discover(oop obj, ReferenceType type) {

   207   log_trace(gc, ref)("Discovered Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));

   208 

   209   // Update statistics

   210   _discovered_count.get()[type]++;

   211 

   212   // Mark referent finalizable

   213   if (should_mark_referent(type)) {

   214     oop* const referent_addr = (oop*)java_lang_ref_Reference::referent_addr_raw(obj);

   215     ZBarrier::mark_barrier_on_oop_field(referent_addr, true /* finalizable */);

   216   }

   217 

   218   // Add reference to discovered list

   219   assert(java_lang_ref_Reference::discovered(obj) == NULL, "Already discovered");

   220   oop* const list = _discovered_list.addr();

   221   java_lang_ref_Reference::set_discovered(obj, *list);

   222   *list = obj;

   223 }

   224 

   225 oop ZReferenceProcessor::drop(oop obj, ReferenceType type) {

   226   log_trace(gc, ref)("Dropped Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));

   227 

   228   // Keep referent alive

   229   keep_referent_alive(obj, type);

   230 

   231   // Unlink and return next in list

   232   const oop next = java_lang_ref_Reference::discovered(obj);

   233   java_lang_ref_Reference::set_discovered(obj, NULL);

   234   return next;

   235 }

   236 

   237 oop* ZReferenceProcessor::keep(oop obj, ReferenceType type) {

   238   log_trace(gc, ref)("Enqueued Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));

   239 

   240   // Update statistics

   241   _enqueued_count.get()[type]++;

   242 

   243   // Clear referent

   244   if (should_clear_referent(type)) {

   245     java_lang_ref_Reference::set_referent(obj, NULL);

   246   }

   247 

   248   // Make reference inactive by self-looping the next field. We could be racing with a

   249   // call to Reference.enqueue() from the application, which is why we are using a CAS

   250   // to make sure we change the next field only if it is NULL. A failing CAS means the

   251   // reference has already been enqueued. However, we don't check the result of the CAS,

   252   // since we still have no option other than keeping the reference on the pending list.

   253   // It's ok to have the reference both on the pending list and enqueued at the same

   254   // time (the pending list is linked through the discovered field, while the reference

   255   // queue is linked through the next field). When the ReferenceHandler thread later

   256   // calls Reference.enqueue() we detect that it has already been enqueued and drop it.

   257   oop* const next_addr = (oop*)java_lang_ref_Reference::next_addr_raw(obj);

   258   Atomic::cmpxchg(obj, next_addr, oop(NULL));

   259 

   260   // Return next in list

   261   return (oop*)java_lang_ref_Reference::discovered_addr_raw(obj);

   262 }

   263 

   264 void ZReferenceProcessor::work() {

   265   // Process discovered references

   266   oop* const list = _discovered_list.addr();

   267   oop* p = list;

   268 

   269   while (*p != NULL) {

   270     const oop obj = *p;

   271     const ReferenceType type = reference_type(obj);

   272 

   273     if (should_drop_reference(obj, type)) {

   274       *p = drop(obj, type);

   275     } else {

   276       p = keep(obj, type);

   277     }

   278   }

   279 

   280   // Prepend discovered references to internal pending list

   281   if (*list != NULL) {

   282     *p = Atomic::xchg(*list, _pending_list.addr());

   283     if (*p == NULL) {

   284       // First to prepend to list, record tail

   285       _pending_list_tail = p;

   286     }

   287 

   288     // Clear discovered list

   289     *list = NULL;

   290   }

   291 }

   292 

   293 bool ZReferenceProcessor::is_empty() const {

   294   ZPerWorkerConstIterator<oop> iter(&_discovered_list);

   295   for (const oop* list; iter.next(&list);) {

   296     if (*list != NULL) {

   297       return false;

   298     }

   299   }

   300 

   301   if (_pending_list.get() != NULL) {

   302     return false;

   303   }

   304 

   305   return true;

   306 }

   307 

   308 void ZReferenceProcessor::reset_statistics() {

   309   assert(is_empty(), "Should be empty");

   310 

   311   // Reset encountered

   312   ZPerWorkerIterator<Counters> iter_encountered(&_encountered_count);

   313   for (Counters* counters; iter_encountered.next(&counters);) {

   314     for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {

   315       (*counters)[i] = 0;

   316     }

   317   }

   318 

   319   // Reset discovered

   320   ZPerWorkerIterator<Counters> iter_discovered(&_discovered_count);

   321   for (Counters* counters; iter_discovered.next(&counters);) {

   322     for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {

   323       (*counters)[i] = 0;

   324     }

   325   }

   326 

   327   // Reset enqueued

   328   ZPerWorkerIterator<Counters> iter_enqueued(&_enqueued_count);

   329   for (Counters* counters; iter_enqueued.next(&counters);) {

   330     for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {

   331       (*counters)[i] = 0;

   332     }

   333   }

   334 }

   335 

   336 void ZReferenceProcessor::collect_statistics() {

   337   Counters encountered = {};

   338   Counters discovered = {};

   339   Counters enqueued = {};

   340 

   341   // Sum encountered

   342   ZPerWorkerConstIterator<Counters> iter_encountered(&_encountered_count);

   343   for (const Counters* counters; iter_encountered.next(&counters);) {

   344     for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {

   345       encountered[i] += (*counters)[i];

   346     }

   347   }

   348 

   349   // Sum discovered

   350   ZPerWorkerConstIterator<Counters> iter_discovered(&_discovered_count);

   351   for (const Counters* counters; iter_discovered.next(&counters);) {

   352     for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {

   353       discovered[i] += (*counters)[i];

   354     }

   355   }

   356 

   357   // Sum enqueued

   358   ZPerWorkerConstIterator<Counters> iter_enqueued(&_enqueued_count);

   359   for (const Counters* counters; iter_enqueued.next(&counters);) {

   360     for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {

   361       enqueued[i] += (*counters)[i];

   362     }

   363   }

   364 

   365   // Update statistics

   366   ZStatReferences::set_soft(encountered[REF_SOFT], discovered[REF_SOFT], enqueued[REF_SOFT]);

   367   ZStatReferences::set_weak(encountered[REF_WEAK], discovered[REF_WEAK], enqueued[REF_WEAK]);

   368   ZStatReferences::set_final(encountered[REF_FINAL], discovered[REF_FINAL], enqueued[REF_FINAL]);

   369   ZStatReferences::set_phantom(encountered[REF_PHANTOM], discovered[REF_PHANTOM], enqueued[REF_PHANTOM]);

   370 

   371   // Trace statistics

   372   const ReferenceProcessorStats stats(discovered[REF_SOFT],

   373                                       discovered[REF_WEAK],

   374                                       discovered[REF_FINAL],

   375                                       discovered[REF_PHANTOM]);

   376   ZTracer::tracer()->report_gc_reference_stats(stats);

   377 }

   378 

   379 class ZReferenceProcessorTask : public ZTask {

   380 private:

   381   ZReferenceProcessor* const _reference_processor;

   382 

   383 public:

   384   ZReferenceProcessorTask(ZReferenceProcessor* reference_processor) :

   385       ZTask("ZReferenceProcessorTask"),

   386       _reference_processor(reference_processor) {}

   387 

   388   virtual void work() {

   389     _reference_processor->work();

   390   }

   391 };

   392 

   393 void ZReferenceProcessor::process_references() {

   394   ZStatTimer timer(ZSubPhaseConcurrentReferencesProcess);

   395 

   396   // Process discovered lists

   397   ZReferenceProcessorTask task(this);

   398   _workers->run_concurrent(&task);

   399 

   400   // Update soft reference clock

   401   update_soft_reference_clock();

   402 

   403   // Collect, log and trace statistics

   404   collect_statistics();

   405 }

   406 

   407 void ZReferenceProcessor::enqueue_references() {

   408   ZStatTimer timer(ZSubPhaseConcurrentReferencesEnqueue);

   409 

   410   if (_pending_list.get() == NULL) {

   411     // Nothing to enqueue

   412     return;

   413   }

   414 

   415   {

   416     // Heap_lock protects external pending list

   417     MonitorLockerEx ml(Heap_lock);

   418 

   419     // Prepend internal pending list to external pending list

   420     *_pending_list_tail = Universe::swap_reference_pending_list(_pending_list.get());

   421 

   422     // Notify ReferenceHandler thread

   423     ml.notify_all();

   424   }

   425 

   426   // Reset internal pending list

   427   _pending_list.set(NULL);

   428   _pending_list_tail = _pending_list.addr();

   429 }