1 /*

     2  * Copyright (c) 2001, 2015, 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 

    25 #include "precompiled.hpp"

    26 #include "gc/g1/g1CollectedHeap.inline.hpp"

    27 #include "gc/g1/satbQueue.hpp"

    28 #include "gc/shared/collectedHeap.hpp"

    29 #include "memory/allocation.inline.hpp"

    30 #include "oops/oop.inline.hpp"

    31 #include "runtime/mutexLocker.hpp"

    32 #include "runtime/safepoint.hpp"

    33 #include "runtime/thread.hpp"

    34 #include "runtime/vmThread.hpp"

    35 

    36 ObjPtrQueue::ObjPtrQueue(SATBMarkQueueSet* qset, bool permanent) :

    37   // SATB queues are only active during marking cycles. We create

    38   // them with their active field set to false. If a thread is

    39   // created during a cycle and its SATB queue needs to be activated

    40   // before the thread starts running, we'll need to set its active

    41   // field to true. This is done in JavaThread::initialize_queues().

    42   PtrQueue(qset, permanent, false /* active */)

    43 { }

    44 

    45 void ObjPtrQueue::flush() {

    46   // Filter now to possibly save work later.  If filtering empties the

    47   // buffer then flush_impl can deallocate the buffer.

    48   filter();

    49   flush_impl();

    50 }

    51 

    52 // Return true if a SATB buffer entry refers to an object that

    53 // requires marking.

    54 //

    55 // The entry must point into the G1 heap.  In particular, it must not

    56 // be a NULL pointer.  NULL pointers are pre-filtered and never

    57 // inserted into a SATB buffer.

    58 //

    59 // An entry that is below the NTAMS pointer for the containing heap

    60 // region requires marking. Such an entry must point to a valid object.

    61 //

    62 // An entry that is at least the NTAMS pointer for the containing heap

    63 // region might be any of the following, none of which should be marked.

    64 //

    65 // * A reference to an object allocated since marking started.

    66 //   According to SATB, such objects are implicitly kept live and do

    67 //   not need to be dealt with via SATB buffer processing.

    68 //

    69 // * A reference to a young generation object. Young objects are

    70 //   handled separately and are not marked by concurrent marking.

    71 //

    72 // * A stale reference to a young generation object. If a young

    73 //   generation object reference is recorded and not filtered out

    74 //   before being moved by a young collection, the reference becomes

    75 //   stale.

    76 //

    77 // * A stale reference to an eagerly reclaimed humongous object.  If a

    78 //   humongous object is recorded and then reclaimed, the reference

    79 //   becomes stale.

    80 //

    81 // The stale reference cases are implicitly handled by the NTAMS

    82 // comparison. Because of the possibility of stale references, buffer

    83 // processing must be somewhat circumspect and not assume entries

    84 // in an unfiltered buffer refer to valid objects.

    85 

    86 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {

    87   // Includes rejection of NULL pointers.

    88   assert(heap->is_in_reserved(entry),

    89          "Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry));

    90 

    91   HeapRegion* region = heap->heap_region_containing(entry);

    92   assert(region != NULL, "No region for " PTR_FORMAT, p2i(entry));

    93   if (entry >= region->next_top_at_mark_start()) {

    94     return false;

    95   }

    96 

    97   assert(((oop)entry)->is_oop(true /* ignore mark word */),

    98          "Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry));

    99 

   100   return true;

   101 }

   102 

   103 // This method removes entries from a SATB buffer that will not be

   104 // useful to the concurrent marking threads.  Entries are retained if

   105 // they require marking and are not already marked. Retained entries

   106 // are compacted toward the top of the buffer.

   107 

   108 void ObjPtrQueue::filter() {

   109   G1CollectedHeap* g1h = G1CollectedHeap::heap();

   110   void** buf = _buf;

   111 

   112   if (buf == NULL) {

   113     // nothing to do

   114     return;

   115   }

   116 

   117   // Used for sanity checking at the end of the loop.

   118   DEBUG_ONLY(size_t entries = 0; size_t retained = 0;)

   119 

   120   assert(_index <= _sz, "invariant");

   121   void** limit = &buf[byte_index_to_index(_index)];

   122   void** src = &buf[byte_index_to_index(_sz)];

   123   void** dst = src;

   124 

   125   while (limit < src) {

   126     DEBUG_ONLY(entries += 1;)

   127     --src;

   128     void* entry = *src;

   129     // NULL the entry so that unused parts of the buffer contain NULLs

   130     // at the end. If we are going to retain it we will copy it to its

   131     // final place. If we have retained all entries we have visited so

   132     // far, we'll just end up copying it to the same place.

   133     *src = NULL;

   134 

   135     if (requires_marking(entry, g1h) && !g1h->isMarkedNext((oop)entry)) {

   136       --dst;

   137       assert(*dst == NULL, "filtering destination should be clear");

   138       *dst = entry;

   139       DEBUG_ONLY(retained += 1;);

   140     }

   141   }

   142   size_t new_index = pointer_delta(dst, buf, 1);

   143 

   144 #ifdef ASSERT

   145   size_t entries_calc = (_sz - _index) / sizeof(void*);

   146   assert(entries == entries_calc, "the number of entries we counted "

   147          "should match the number of entries we calculated");

   148   size_t retained_calc = (_sz - new_index) / sizeof(void*);

   149   assert(retained == retained_calc, "the number of retained entries we counted "

   150          "should match the number of retained entries we calculated");

   151 #endif // ASSERT

   152 

   153   _index = new_index;

   154 }

   155 

   156 // This method will first apply the above filtering to the buffer. If

   157 // post-filtering a large enough chunk of the buffer has been cleared

   158 // we can re-use the buffer (instead of enqueueing it) and we can just

   159 // allow the mutator to carry on executing using the same buffer

   160 // instead of replacing it.

   161 

   162 bool ObjPtrQueue::should_enqueue_buffer() {

   163   assert(_lock == NULL || _lock->owned_by_self(),

   164          "we should have taken the lock before calling this");

   165 

   166   // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.

   167 

   168   // This method should only be called if there is a non-NULL buffer

   169   // that is full.

   170   assert(_index == 0, "pre-condition");

   171   assert(_buf != NULL, "pre-condition");

   172 

   173   filter();

   174 

   175   size_t percent_used = ((_sz - _index) * 100) / _sz;

   176   bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;

   177   return should_enqueue;

   178 }

   179 

   180 void ObjPtrQueue::apply_closure_and_empty(SATBBufferClosure* cl) {

   181   assert(SafepointSynchronize::is_at_safepoint(),

   182          "SATB queues must only be processed at safepoints");

   183   if (_buf != NULL) {

   184     assert(_index % sizeof(void*) == 0, "invariant");

   185     assert(_sz % sizeof(void*) == 0, "invariant");

   186     assert(_index <= _sz, "invariant");

   187     cl->do_buffer(_buf + byte_index_to_index(_index),

   188                   byte_index_to_index(_sz - _index));

   189     _index = _sz;

   190   }

   191 }

   192 

   193 #ifndef PRODUCT

   194 // Helpful for debugging

   195 

   196 void ObjPtrQueue::print(const char* name) {

   197   print(name, _buf, _index, _sz);

   198 }

   199 

   200 void ObjPtrQueue::print(const char* name,

   201                         void** buf, size_t index, size_t sz) {

   202   gclog_or_tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " "

   203                          "index: " SIZE_FORMAT " sz: " SIZE_FORMAT,

   204                          name, p2i(buf), index, sz);

   205 }

   206 #endif // PRODUCT

   207 

   208 SATBMarkQueueSet::SATBMarkQueueSet() :

   209   PtrQueueSet(),

   210   _shared_satb_queue(this, true /* permanent */) { }

   211 

   212 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,

   213                                   int process_completed_threshold,

   214                                   Mutex* lock) {

   215   PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);

   216   _shared_satb_queue.set_lock(lock);

   217 }

   218 

   219 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {

   220   t->satb_mark_queue().handle_zero_index();

   221 }

   222 

   223 #ifdef ASSERT

   224 void SATBMarkQueueSet::dump_active_states(bool expected_active) {

   225   gclog_or_tty->print_cr("Expected SATB active state: %s",

   226                          expected_active ? "ACTIVE" : "INACTIVE");

   227   gclog_or_tty->print_cr("Actual SATB active states:");

   228   gclog_or_tty->print_cr("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");

   229   for (JavaThread* t = Threads::first(); t; t = t->next()) {

   230     gclog_or_tty->print_cr("  Thread \"%s\" queue: %s", t->name(),

   231                            t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");

   232   }

   233   gclog_or_tty->print_cr("  Shared queue: %s",

   234                          shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");

   235 }

   236 

   237 void SATBMarkQueueSet::verify_active_states(bool expected_active) {

   238   // Verify queue set state

   239   if (is_active() != expected_active) {

   240     dump_active_states(expected_active);

   241     guarantee(false, "SATB queue set has an unexpected active state");

   242   }

   243 

   244   // Verify thread queue states

   245   for (JavaThread* t = Threads::first(); t; t = t->next()) {

   246     if (t->satb_mark_queue().is_active() != expected_active) {

   247       dump_active_states(expected_active);

   248       guarantee(false, "Thread SATB queue has an unexpected active state");

   249     }

   250   }

   251 

   252   // Verify shared queue state

   253   if (shared_satb_queue()->is_active() != expected_active) {

   254     dump_active_states(expected_active);

   255     guarantee(false, "Shared SATB queue has an unexpected active state");

   256   }

   257 }

   258 #endif // ASSERT

   259 

   260 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {

   261   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");

   262 #ifdef ASSERT

   263   verify_active_states(expected_active);

   264 #endif // ASSERT

   265   _all_active = active;

   266   for (JavaThread* t = Threads::first(); t; t = t->next()) {

   267     t->satb_mark_queue().set_active(active);

   268   }

   269   shared_satb_queue()->set_active(active);

   270 }

   271 

   272 void SATBMarkQueueSet::filter_thread_buffers() {

   273   for(JavaThread* t = Threads::first(); t; t = t->next()) {

   274     t->satb_mark_queue().filter();

   275   }

   276   shared_satb_queue()->filter();

   277 }

   278 

   279 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {

   280   BufferNode* nd = NULL;

   281   {

   282     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

   283     if (_completed_buffers_head != NULL) {

   284       nd = _completed_buffers_head;

   285       _completed_buffers_head = nd->next();

   286       if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;

   287       _n_completed_buffers--;

   288       if (_n_completed_buffers == 0) _process_completed = false;

   289     }

   290   }

   291   if (nd != NULL) {

   292     void **buf = BufferNode::make_buffer_from_node(nd);

   293     // Skip over NULL entries at beginning (e.g. push end) of buffer.

   294     // Filtering can result in non-full completed buffers; see

   295     // should_enqueue_buffer.

   296     assert(_sz % sizeof(void*) == 0, "invariant");

   297     size_t limit = ObjPtrQueue::byte_index_to_index(_sz);

   298     for (size_t i = 0; i < limit; ++i) {

   299       if (buf[i] != NULL) {

   300         // Found the end of the block of NULLs; process the remainder.

   301         cl->do_buffer(buf + i, limit - i);

   302         break;

   303       }

   304     }

   305     deallocate_buffer(buf);

   306     return true;

   307   } else {

   308     return false;

   309   }

   310 }

   311 

   312 #ifndef PRODUCT

   313 // Helpful for debugging

   314 

   315 #define SATB_PRINTER_BUFFER_SIZE 256

   316 

   317 void SATBMarkQueueSet::print_all(const char* msg) {

   318   char buffer[SATB_PRINTER_BUFFER_SIZE];

   319   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");

   320 

   321   gclog_or_tty->cr();

   322   gclog_or_tty->print_cr("SATB BUFFERS [%s]", msg);

   323 

   324   BufferNode* nd = _completed_buffers_head;

   325   int i = 0;

   326   while (nd != NULL) {

   327     void** buf = BufferNode::make_buffer_from_node(nd);

   328     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);

   329     ObjPtrQueue::print(buffer, buf, 0, _sz);

   330     nd = nd->next();

   331     i += 1;

   332   }

   333 

   334   for (JavaThread* t = Threads::first(); t; t = t->next()) {

   335     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());

   336     t->satb_mark_queue().print(buffer);

   337   }

   338 

   339   shared_satb_queue()->print("Shared");

   340 

   341   gclog_or_tty->cr();

   342 }

   343 #endif // PRODUCT

   344 

   345 void SATBMarkQueueSet::abandon_partial_marking() {

   346   BufferNode* buffers_to_delete = NULL;

   347   {

   348     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

   349     while (_completed_buffers_head != NULL) {

   350       BufferNode* nd = _completed_buffers_head;

   351       _completed_buffers_head = nd->next();

   352       nd->set_next(buffers_to_delete);

   353       buffers_to_delete = nd;

   354     }

   355     _completed_buffers_tail = NULL;

   356     _n_completed_buffers = 0;

   357     DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());

   358   }

   359   while (buffers_to_delete != NULL) {

   360     BufferNode* nd = buffers_to_delete;

   361     buffers_to_delete = nd->next();

   362     deallocate_buffer(BufferNode::make_buffer_from_node(nd));

   363   }

   364   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");

   365   // So we can safely manipulate these queues.

   366   for (JavaThread* t = Threads::first(); t; t = t->next()) {

   367     t->satb_mark_queue().reset();

   368   }

   369  shared_satb_queue()->reset();

   370 }