--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/gc/g1/ptrQueue.cpp	Wed May 13 15:16:06 2015 +0200
@@ -0,0 +1,299 @@
+/*
+ * 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/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), _sz(0), _active(active),
+  _perm(perm), _lock(NULL)
+{}
+
+PtrQueue::~PtrQueue() {
+  assert(_perm || (_buf == NULL), "queue must be flushed before delete");
+}
+
+void PtrQueue::flush_impl() {
+  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;
+  }
+}
+
+
+void PtrQueue::enqueue_known_active(void* ptr) {
+  assert(_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(_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 enqueue_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);
+    _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 enqueueing 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 enqueueing 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;
+}
+
+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();
+  }
+}