1 /*
  2  * Copyright (c) 2001, 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 
 25 #include "precompiled.hpp"
 26 #include "jvm.h"
 27 #include "gc/g1/g1CollectedHeap.inline.hpp"
 28 #include "gc/g1/satbMarkQueue.hpp"
 29 #include "gc/shared/collectedHeap.hpp"
 30 #include "memory/allocation.inline.hpp"
 31 #include "oops/oop.inline.hpp"
 32 #include "runtime/mutexLocker.hpp"
 33 #include "runtime/safepoint.hpp"
 34 #include "runtime/thread.hpp"
 35 #include "runtime/threadSMR.hpp"
 36 #include "runtime/vmThread.hpp"
 37 
 38 SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent) :
 39   // SATB queues are only active during marking cycles. We create
 40   // them with their active field set to false. If a thread is
 41   // created during a cycle and its SATB queue needs to be activated
 42   // before the thread starts running, we'll need to set its active
 43   // field to true. This is done in G1SBarrierSet::on_thread_attach().
 44   PtrQueue(qset, permanent, false /* active */)
 45 { }
 46 
 47 void SATBMarkQueue::flush() {
 48   // Filter now to possibly save work later.  If filtering empties the
 49   // buffer then flush_impl can deallocate the buffer.
 50   filter();
 51   flush_impl();
 52 }
 53 
 54 // Return true if a SATB buffer entry refers to an object that
 55 // requires marking.
 56 //
 57 // The entry must point into the G1 heap.  In particular, it must not
 58 // be a NULL pointer.  NULL pointers are pre-filtered and never
 59 // inserted into a SATB buffer.
 60 //
 61 // An entry that is below the NTAMS pointer for the containing heap
 62 // region requires marking. Such an entry must point to a valid object.
 63 //
 64 // An entry that is at least the NTAMS pointer for the containing heap
 65 // region might be any of the following, none of which should be marked.
 66 //
 67 // * A reference to an object allocated since marking started.
 68 //   According to SATB, such objects are implicitly kept live and do
 69 //   not need to be dealt with via SATB buffer processing.
 70 //
 71 // * A reference to a young generation object. Young objects are
 72 //   handled separately and are not marked by concurrent marking.
 73 //
 74 // * A stale reference to a young generation object. If a young
 75 //   generation object reference is recorded and not filtered out
 76 //   before being moved by a young collection, the reference becomes
 77 //   stale.
 78 //
 79 // * A stale reference to an eagerly reclaimed humongous object.  If a
 80 //   humongous object is recorded and then reclaimed, the reference
 81 //   becomes stale.
 82 //
 83 // The stale reference cases are implicitly handled by the NTAMS
 84 // comparison. Because of the possibility of stale references, buffer
 85 // processing must be somewhat circumspect and not assume entries
 86 // in an unfiltered buffer refer to valid objects.
 87 
 88 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
 89   // Includes rejection of NULL pointers.
 90   assert(heap->is_in_reserved(entry),
 91          "Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry));
 92 
 93   HeapRegion* region = heap->heap_region_containing(entry);
 94   assert(region != NULL, "No region for " PTR_FORMAT, p2i(entry));
 95   if (entry >= region->next_top_at_mark_start()) {
 96     return false;
 97   }
 98 
 99   assert(oopDesc::is_oop(oop(entry), true /* ignore mark word */),
100          "Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry));
101 
102   return true;
103 }
104 
105 inline bool retain_entry(const void* entry, G1CollectedHeap* heap) {
106   return requires_marking(entry, heap) && !heap->is_marked_next((oop)entry);
107 }
108 
109 // This method removes entries from a SATB buffer that will not be
110 // useful to the concurrent marking threads.  Entries are retained if
111 // they require marking and are not already marked. Retained entries
112 // are compacted toward the top of the buffer.
113 
114 void SATBMarkQueue::filter() {
115   G1CollectedHeap* g1h = G1CollectedHeap::heap();
116   void** buf = _buf;
117 
118   if (buf == NULL) {
119     // nothing to do
120     return;
121   }
122 
123   // Two-fingered compaction toward the end.
124   void** src = &buf[index()];
125   void** dst = &buf[capacity()];
126   assert(src <= dst, "invariant");
127   for ( ; src < dst; ++src) {
128     // Search low to high for an entry to keep.
129     void* entry = *src;
130     if (retain_entry(entry, g1h)) {
131       // Found keeper.  Search high to low for an entry to discard.
132       while (src < --dst) {
133         if (!retain_entry(*dst, g1h)) {
134           *dst = entry;         // Replace discard with keeper.
135           break;
136         }
137       }
138       // If discard search failed (src == dst), the outer loop will also end.
139     }
140   }
141   // dst points to the lowest retained entry, or the end of the buffer
142   // if all the entries were filtered out.
143   set_index(dst - buf);
144 }
145 
146 // This method will first apply the above filtering to the buffer. If
147 // post-filtering a large enough chunk of the buffer has been cleared
148 // we can re-use the buffer (instead of enqueueing it) and we can just
149 // allow the mutator to carry on executing using the same buffer
150 // instead of replacing it.
151 
152 bool SATBMarkQueue::should_enqueue_buffer() {
153   assert(_lock == NULL || _lock->owned_by_self(),
154          "we should have taken the lock before calling this");
155 
156   // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
157 
158   // This method should only be called if there is a non-NULL buffer
159   // that is full.
160   assert(index() == 0, "pre-condition");
161   assert(_buf != NULL, "pre-condition");
162 
163   filter();
164 
165   size_t cap = capacity();
166   size_t percent_used = ((cap - index()) * 100) / cap;
167   bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
168   return should_enqueue;
169 }
170 
171 void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
172   assert(SafepointSynchronize::is_at_safepoint(),
173          "SATB queues must only be processed at safepoints");
174   if (_buf != NULL) {
175     cl->do_buffer(&_buf[index()], size());
176     reset();
177   }
178 }
179 
180 #ifndef PRODUCT
181 // Helpful for debugging
182 
183 static void print_satb_buffer(const char* name,
184                               void** buf,
185                               size_t index,
186                               size_t capacity) {
187   tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT
188                 " capacity: " SIZE_FORMAT,
189                 name, p2i(buf), index, capacity);
190 }
191 
192 void SATBMarkQueue::print(const char* name) {
193   print_satb_buffer(name, _buf, index(), capacity());
194 }
195 
196 #endif // PRODUCT
197 
198 SATBMarkQueueSet::SATBMarkQueueSet() :
199   PtrQueueSet(),
200   _shared_satb_queue(this, true /* permanent */) { }
201 
202 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
203                                   int process_completed_threshold,
204                                   Mutex* lock) {
205   PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
206   _shared_satb_queue.set_lock(lock);
207 }
208 
209 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
210   t->satb_mark_queue().handle_zero_index();
211 }
212 
213 #ifdef ASSERT
214 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
215   log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");
216   log_error(gc, verify)("Actual SATB active states:");
217   log_error(gc, verify)("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
218   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
219     log_error(gc, verify)("  Thread \"%s\" queue: %s", t->name(), t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");
220   }
221   log_error(gc, verify)("  Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
222 }
223 
224 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
225   // Verify queue set state
226   if (is_active() != expected_active) {
227     dump_active_states(expected_active);
228     guarantee(false, "SATB queue set has an unexpected active state");
229   }
230 
231   // Verify thread queue states
232   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
233     if (t->satb_mark_queue().is_active() != expected_active) {
234       dump_active_states(expected_active);
235       guarantee(false, "Thread SATB queue has an unexpected active state");
236     }
237   }
238 
239   // Verify shared queue state
240   if (shared_satb_queue()->is_active() != expected_active) {
241     dump_active_states(expected_active);
242     guarantee(false, "Shared SATB queue has an unexpected active state");
243   }
244 }
245 #endif // ASSERT
246 
247 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
248   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
249 #ifdef ASSERT
250   verify_active_states(expected_active);
251 #endif // ASSERT
252   _all_active = active;
253   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
254     t->satb_mark_queue().set_active(active);
255   }
256   shared_satb_queue()->set_active(active);
257 }
258 
259 void SATBMarkQueueSet::filter_thread_buffers() {
260   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
261     t->satb_mark_queue().filter();
262   }
263   shared_satb_queue()->filter();
264 }
265 
266 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
267   BufferNode* nd = NULL;
268   {
269     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
270     if (_completed_buffers_head != NULL) {
271       nd = _completed_buffers_head;
272       _completed_buffers_head = nd->next();
273       if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
274       _n_completed_buffers--;
275       if (_n_completed_buffers == 0) _process_completed = false;
276     }
277   }
278   if (nd != NULL) {
279     void **buf = BufferNode::make_buffer_from_node(nd);
280     size_t index = nd->index();
281     size_t size = buffer_size();
282     assert(index <= size, "invariant");
283     cl->do_buffer(buf + index, size - index);
284     deallocate_buffer(nd);
285     return true;
286   } else {
287     return false;
288   }
289 }
290 
291 #ifndef PRODUCT
292 // Helpful for debugging
293 
294 #define SATB_PRINTER_BUFFER_SIZE 256
295 
296 void SATBMarkQueueSet::print_all(const char* msg) {
297   char buffer[SATB_PRINTER_BUFFER_SIZE];
298   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
299 
300   tty->cr();
301   tty->print_cr("SATB BUFFERS [%s]", msg);
302 
303   BufferNode* nd = _completed_buffers_head;
304   int i = 0;
305   while (nd != NULL) {
306     void** buf = BufferNode::make_buffer_from_node(nd);
307     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
308     print_satb_buffer(buffer, buf, nd->index(), buffer_size());
309     nd = nd->next();
310     i += 1;
311   }
312 
313   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
314     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
315     t->satb_mark_queue().print(buffer);
316   }
317 
318   shared_satb_queue()->print("Shared");
319 
320   tty->cr();
321 }
322 #endif // PRODUCT
323 
324 void SATBMarkQueueSet::abandon_partial_marking() {
325   BufferNode* buffers_to_delete = NULL;
326   {
327     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
328     while (_completed_buffers_head != NULL) {
329       BufferNode* nd = _completed_buffers_head;
330       _completed_buffers_head = nd->next();
331       nd->set_next(buffers_to_delete);
332       buffers_to_delete = nd;
333     }
334     _completed_buffers_tail = NULL;
335     _n_completed_buffers = 0;
336     DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
337   }
338   while (buffers_to_delete != NULL) {
339     BufferNode* nd = buffers_to_delete;
340     buffers_to_delete = nd->next();
341     deallocate_buffer(nd);
342   }
343   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
344   // So we can safely manipulate these queues.
345   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
346     t->satb_mark_queue().reset();
347   }
348   shared_satb_queue()->reset();
349 }