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 /*

  * Copyright (c) 2001, 2012, 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_implementation/g1/ptrQueue.hpp"

 #include "memory/allocation.hpp"

 #include "memory/allocation.inline.hpp"

 #include "runtime/mutex.hpp"

 #include "runtime/mutexLocker.hpp"

 #include "runtime/thread.inline.hpp"

 PtrQueue::PtrQueue(PtrQueueSet* qset, bool perm, bool active) :

   _qset(qset), _buf(NULL), _index(0), _active(active),

   _perm(perm), _lock(NULL)

 {}

 void PtrQueue::flush() {

   if (!_perm && _buf != NULL) {

     if (_index == _sz) {

       // No work to do.

       qset()->deallocate_buffer(_buf);

     } else {

       // We must NULL out the unused entries, then enqueue.

       for (size_t i = 0; i < _index; i += oopSize) {

         _buf[byte_index_to_index((int)i)] = NULL;

       }

       qset()->enqueue_complete_buffer(_buf);

     }

     _buf = NULL;

     _index = 0;

   }

 }

 static int byte_index_to_index(int ind) {

   assert((ind % oopSize) == 0, "Invariant.");

   return ind / oopSize;

 }

 static int index_to_byte_index(int byte_ind) {

   return byte_ind * oopSize;

 }

 void PtrQueue::enqueue_known_active(void* ptr) {

   assert(0 <= _index && _index <= _sz, "Invariant.");

   assert(_index == 0 || _buf != NULL, "invariant");

   while (_index == 0) {

     handle_zero_index();

   }

   assert(_index > 0, "postcondition");

   _index -= oopSize;

   _buf[byte_index_to_index((int)_index)] = ptr;

   assert(0 <= _index && _index <= _sz, "Invariant.");

 }

 void PtrQueue::locking_enqueue_completed_buffer(void** buf) {

   assert(_lock->owned_by_self(), "Required.");

   // We have to unlock _lock (which may be Shared_DirtyCardQ_lock) before

   // we acquire DirtyCardQ_CBL_mon inside enqeue_complete_buffer as they

   // have the same rank and we may get the "possible deadlock" message

   _lock->unlock();

   qset()->enqueue_complete_buffer(buf);

   // We must relock only because the caller will unlock, for the normal

   // case.

   _lock->lock_without_safepoint_check();

 }

 PtrQueueSet::PtrQueueSet(bool notify_when_complete) :

   _max_completed_queue(0),

   _cbl_mon(NULL), _fl_lock(NULL),

   _notify_when_complete(notify_when_complete),

   _sz(0),

   _completed_buffers_head(NULL),

   _completed_buffers_tail(NULL),

   _n_completed_buffers(0),

   _process_completed_threshold(0), _process_completed(false),

   _buf_free_list(NULL), _buf_free_list_sz(0)

 {

   _fl_owner = this;

 }

 void** PtrQueueSet::allocate_buffer() {

   assert(_sz > 0, "Didn't set a buffer size.");

   MutexLockerEx x(_fl_owner->_fl_lock, Mutex::_no_safepoint_check_flag);

   if (_fl_owner->_buf_free_list != NULL) {

     void** res = BufferNode::make_buffer_from_node(_fl_owner->_buf_free_list);

     _fl_owner->_buf_free_list = _fl_owner->_buf_free_list->next();

     _fl_owner->_buf_free_list_sz--;

     return res;

   } else {

     // Allocate space for the BufferNode in front of the buffer.

     char *b =  NEW_C_HEAP_ARRAY(char, _sz + BufferNode::aligned_size(), mtGC);

     return BufferNode::make_buffer_from_block(b);

   }

 }

 void PtrQueueSet::deallocate_buffer(void** buf) {

   assert(_sz > 0, "Didn't set a buffer size.");

   MutexLockerEx x(_fl_owner->_fl_lock, Mutex::_no_safepoint_check_flag);

   BufferNode *node = BufferNode::make_node_from_buffer(buf);

   node->set_next(_fl_owner->_buf_free_list);

   _fl_owner->_buf_free_list = node;

   _fl_owner->_buf_free_list_sz++;

 }

 void PtrQueueSet::reduce_free_list() {

   assert(_fl_owner == this, "Free list reduction is allowed only for the owner");

   // For now we'll adopt the strategy of deleting half.

   MutexLockerEx x(_fl_lock, Mutex::_no_safepoint_check_flag);

   size_t n = _buf_free_list_sz / 2;

   while (n > 0) {

     assert(_buf_free_list != NULL, "_buf_free_list_sz must be wrong.");

     void* b = BufferNode::make_block_from_node(_buf_free_list);

     _buf_free_list = _buf_free_list->next();

     FREE_C_HEAP_ARRAY(char, b, mtGC);

     _buf_free_list_sz --;

     n--;

   }

 }

 void PtrQueue::handle_zero_index() {

   assert(_index == 0, "Precondition.");

   // This thread records the full buffer and allocates a new one (while

   // holding the lock if there is one).

   if (_buf != NULL) {

     if (!should_enqueue_buffer()) {

       assert(_index > 0, "the buffer can only be re-used if it's not full");

       return;

     }

     if (_lock) {

       assert(_lock->owned_by_self(), "Required.");

       // The current PtrQ may be the shared dirty card queue and

       // may be being manipulated by more than one worker thread

       // during a pause. Since the enqueuing of the completed

       // buffer unlocks the Shared_DirtyCardQ_lock more than one

       // worker thread can 'race' on reading the shared queue attributes

       // (_buf and _index) and multiple threads can call into this

       // routine for the same buffer. This will cause the completed

       // buffer to be added to the CBL multiple times.

       // We "claim" the current buffer by caching value of _buf in

       // a local and clearing the field while holding _lock. When

       // _lock is released (while enqueueing the completed buffer)

       // the thread that acquires _lock will skip this code,

       // preventing the subsequent the multiple enqueue, and

       // install a newly allocated buffer below.

       void** buf = _buf;   // local pointer to completed buffer

       _buf = NULL;         // clear shared _buf field

       locking_enqueue_completed_buffer(buf);  // enqueue completed buffer

       // While the current thread was enqueuing the buffer another thread

       // may have a allocated a new buffer and inserted it into this pointer

       // queue. If that happens then we just return so that the current

       // thread doesn't overwrite the buffer allocated by the other thread

       // and potentially losing some dirtied cards.

       if (_buf != NULL) return;

     } else {

       if (qset()->process_or_enqueue_complete_buffer(_buf)) {

         // Recycle the buffer. No allocation.

         _sz = qset()->buffer_size();

         _index = _sz;

         return;

       }

     }

   }

   // Reallocate the buffer

   _buf = qset()->allocate_buffer();

   _sz = qset()->buffer_size();

   _index = _sz;

   assert(0 <= _index && _index <= _sz, "Invariant.");

 }

 bool PtrQueueSet::process_or_enqueue_complete_buffer(void** buf) {

   if (Thread::current()->is_Java_thread()) {

     // We don't lock. It is fine to be epsilon-precise here.

     if (_max_completed_queue == 0 || _max_completed_queue > 0 &&

         _n_completed_buffers >= _max_completed_queue + _completed_queue_padding) {

       bool b = mut_process_buffer(buf);

       if (b) {

         // True here means that the buffer hasn't been deallocated and the caller may reuse it.

         return true;

       }

     }

   }

   // The buffer will be enqueued. The caller will have to get a new one.

   enqueue_complete_buffer(buf);

   return false;

 }

 void PtrQueueSet::enqueue_complete_buffer(void** buf, size_t index) {

   MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

   BufferNode* cbn = BufferNode::new_from_buffer(buf);

   cbn->set_index(index);

   if (_completed_buffers_tail == NULL) {

     assert(_completed_buffers_head == NULL, "Well-formedness");

     _completed_buffers_head = cbn;

     _completed_buffers_tail = cbn;

   } else {

     _completed_buffers_tail->set_next(cbn);

     _completed_buffers_tail = cbn;

   }

   _n_completed_buffers++;

   if (!_process_completed && _process_completed_threshold >= 0 &&

       _n_completed_buffers >= _process_completed_threshold) {

     _process_completed = true;

     if (_notify_when_complete)

       _cbl_mon->notify();

   }

   debug_only(assert_completed_buffer_list_len_correct_locked());

 }

 int PtrQueueSet::completed_buffers_list_length() {

   int n = 0;

   BufferNode* cbn = _completed_buffers_head;

   while (cbn != NULL) {

     n++;

     cbn = cbn->next();

   }

   return n;

 }

 void PtrQueueSet::assert_completed_buffer_list_len_correct() {

   MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

   assert_completed_buffer_list_len_correct_locked();

 }

 void PtrQueueSet::assert_completed_buffer_list_len_correct_locked() {

   guarantee(completed_buffers_list_length() ==  _n_completed_buffers,

             "Completed buffer length is wrong.");

 }

 void PtrQueueSet::set_buffer_size(size_t sz) {

   assert(_sz == 0 && sz > 0, "Should be called only once.");

   _sz = sz * oopSize;

 }

 // Merge lists of buffers. Notify the processing threads.

 // The source queue is emptied as a result. The queues

 // must share the monitor.

 void PtrQueueSet::merge_bufferlists(PtrQueueSet *src) {

   assert(_cbl_mon == src->_cbl_mon, "Should share the same lock");

   MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

   if (_completed_buffers_tail == NULL) {

     assert(_completed_buffers_head == NULL, "Well-formedness");

     _completed_buffers_head = src->_completed_buffers_head;

     _completed_buffers_tail = src->_completed_buffers_tail;

   } else {

     assert(_completed_buffers_head != NULL, "Well formedness");

     if (src->_completed_buffers_head != NULL) {

       _completed_buffers_tail->set_next(src->_completed_buffers_head);

       _completed_buffers_tail = src->_completed_buffers_tail;

     }

   }

   _n_completed_buffers += src->_n_completed_buffers;

   src->_n_completed_buffers = 0;

   src->_completed_buffers_head = NULL;

   src->_completed_buffers_tail = NULL;

   assert(_completed_buffers_head == NULL && _completed_buffers_tail == NULL ||

          _completed_buffers_head != NULL && _completed_buffers_tail != NULL,

          "Sanity");

 }

 void PtrQueueSet::notify_if_necessary() {

   MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

   if (_n_completed_buffers >= _process_completed_threshold || _max_completed_queue == 0) {

     _process_completed = true;

     if (_notify_when_complete)

       _cbl_mon->notify();

   }

 }