/*

 * Copyright (c) 2001, 2015, 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 "gc/g1/g1CollectedHeap.inline.hpp"

#include "gc/g1/satbMarkQueue.hpp"

#include "gc/shared/collectedHeap.hpp"

#include "memory/allocation.inline.hpp"

#include "oops/oop.inline.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/safepoint.hpp"

#include "runtime/thread.hpp"

#include "runtime/vmThread.hpp"

SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent) :

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

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

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

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

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

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

{ }

void SATBMarkQueue::flush() {

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

  // buffer then flush_impl can deallocate the buffer.

  filter();

  flush_impl();

}

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

// requires marking.

//

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

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

// inserted into a SATB buffer.

//

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

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

//

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

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

//

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

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

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

//

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

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

//

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

//   generation object reference is recorded and not filtered out

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

//   stale.

//

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

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

//   becomes stale.

//

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

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

// processing must be somewhat circumspect and not assume entries

// in an unfiltered buffer refer to valid objects.

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

  // Includes rejection of NULL pointers.

  assert(heap->is_in_reserved(entry),

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

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

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

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

    return false;

  }

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

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

  return true;

}

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

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

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

// are compacted toward the top of the buffer.

void SATBMarkQueue::filter() {

  G1CollectedHeap* g1h = G1CollectedHeap::heap();

  void** buf = _buf;

  if (buf == NULL) {

    // nothing to do

    return;

  }

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

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

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

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

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

  void** dst = src;

  while (limit < src) {

    DEBUG_ONLY(entries += 1;)

    --src;

    void* entry = *src;

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

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

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

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

    *src = NULL;

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

      --dst;

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

      *dst = entry;

      DEBUG_ONLY(retained += 1;);

    }

  }

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

#ifdef ASSERT

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

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

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

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

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

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

#endif // ASSERT

  _index = new_index;

}

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

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

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

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

// instead of replacing it.

bool SATBMarkQueue::should_enqueue_buffer() {

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

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

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

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

  // that is full.

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

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

  filter();

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

  bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;

  return should_enqueue;

}

void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {

  assert(SafepointSynchronize::is_at_safepoint(),

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

  if (_buf != NULL) {

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

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

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

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

                  byte_index_to_index(_sz - _index));

    _index = _sz;

  }

}

#ifndef PRODUCT

// Helpful for debugging

void SATBMarkQueue::print(const char* name) {

  print(name, _buf, _index, _sz);

}

void SATBMarkQueue::print(const char* name,

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

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

                         "index: " SIZE_FORMAT " sz: " SIZE_FORMAT,

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

}

#endif // PRODUCT

SATBMarkQueueSet::SATBMarkQueueSet() :

  PtrQueueSet(),

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

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

                                  int process_completed_threshold,

                                  Mutex* lock) {

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

  _shared_satb_queue.set_lock(lock);

}

void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {

  t->satb_mark_queue().handle_zero_index();

}

#ifdef ASSERT

void SATBMarkQueueSet::dump_active_states(bool expected_active) {

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

                         expected_active ? "ACTIVE" : "INACTIVE");

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

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

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

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

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

  }

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

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

}

void SATBMarkQueueSet::verify_active_states(bool expected_active) {

  // Verify queue set state

  if (is_active() != expected_active) {

    dump_active_states(expected_active);

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

  }

  // Verify thread queue states

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

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

      dump_active_states(expected_active);

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

    }

  }

  // Verify shared queue state

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

    dump_active_states(expected_active);

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

  }

}

#endif // ASSERT

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

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

#ifdef ASSERT

  verify_active_states(expected_active);

#endif // ASSERT

  _all_active = active;

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

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

  }

  shared_satb_queue()->set_active(active);

}

void SATBMarkQueueSet::filter_thread_buffers() {

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

    t->satb_mark_queue().filter();

  }

  shared_satb_queue()->filter();

}

bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {

  BufferNode* nd = NULL;

  {

    MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

    if (_completed_buffers_head != NULL) {

      nd = _completed_buffers_head;

      _completed_buffers_head = nd->next();

      if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;

      _n_completed_buffers--;

      if (_n_completed_buffers == 0) _process_completed = false;

    }

  }

  if (nd != NULL) {

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

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

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

    // should_enqueue_buffer.

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

    size_t limit = SATBMarkQueue::byte_index_to_index(_sz);

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

      if (buf[i] != NULL) {

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

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

        break;

      }

    }

    deallocate_buffer(buf);

    return true;

  } else {

    return false;

  }

}

#ifndef PRODUCT

// Helpful for debugging

#define SATB_PRINTER_BUFFER_SIZE 256

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

  char buffer[SATB_PRINTER_BUFFER_SIZE];

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

  gclog_or_tty->cr();

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

  BufferNode* nd = _completed_buffers_head;

  int i = 0;

  while (nd != NULL) {

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

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

    SATBMarkQueue::print(buffer, buf, 0, _sz);

    nd = nd->next();

    i += 1;

  }

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

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

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

  }

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

  gclog_or_tty->cr();

}

#endif // PRODUCT

void SATBMarkQueueSet::abandon_partial_marking() {

  BufferNode* buffers_to_delete = NULL;

  {

    MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

    while (_completed_buffers_head != NULL) {

      BufferNode* nd = _completed_buffers_head;

      _completed_buffers_head = nd->next();

      nd->set_next(buffers_to_delete);

      buffers_to_delete = nd;

    }

    _completed_buffers_tail = NULL;

    _n_completed_buffers = 0;

    DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());

  }

  while (buffers_to_delete != NULL) {

    BufferNode* nd = buffers_to_delete;

    buffers_to_delete = nd->next();

    deallocate_buffer(BufferNode::make_buffer_from_node(nd));

  }

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

  // So we can safely manipulate these queues.

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

    t->satb_mark_queue().reset();

  }

 shared_satb_queue()->reset();

}