--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/gc_implementation/parNew/parGCAllocBuffer.cpp	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,342 @@
+/*
+ * Copyright 2001-2006 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+# include "incls/_precompiled.incl"
+# include "incls/_parGCAllocBuffer.cpp.incl"
+
+ParGCAllocBuffer::ParGCAllocBuffer(size_t desired_plab_sz_) :
+  _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL),
+  _end(NULL), _hard_end(NULL),
+  _retained(false), _retained_filler(),
+  _allocated(0), _wasted(0)
+{
+  assert (min_size() > AlignmentReserve, "Inconsistency!");
+}
+
+const size_t ParGCAllocBuffer::FillerHeaderSize =
+             align_object_size(arrayOopDesc::header_size(T_INT));
+
+// If the minimum object size is greater than MinObjAlignment, we can
+// end up with a shard at the end of the buffer that's smaller than
+// the smallest object.  We can't allow that because the buffer must
+// look like it's full of objects when we retire it, so we make
+// sure we have enough space for a filler int array object.
+const size_t ParGCAllocBuffer::AlignmentReserve =
+             oopDesc::header_size() > MinObjAlignment ? FillerHeaderSize : 0;
+
+void ParGCAllocBuffer::retire(bool end_of_gc, bool retain) {
+  assert(!retain || end_of_gc, "Can only retain at GC end.");
+  if (_retained) {
+    // If the buffer had been retained shorten the previous filler object.
+    assert(_retained_filler.end() <= _top, "INVARIANT");
+    SharedHeap::fill_region_with_object(_retained_filler);
+    // Wasted space book-keeping, otherwise (normally) done in invalidate()
+    _wasted += _retained_filler.word_size();
+    _retained = false;
+  }
+  assert(!end_of_gc || !_retained, "At this point, end_of_gc ==> !_retained.");
+  if (_top < _hard_end) {
+    SharedHeap::fill_region_with_object(MemRegion(_top, _hard_end));
+    if (!retain) {
+      invalidate();
+    } else {
+      // Is there wasted space we'd like to retain for the next GC?
+      if (pointer_delta(_end, _top) > FillerHeaderSize) {
+        _retained = true;
+        _retained_filler = MemRegion(_top, FillerHeaderSize);
+        _top = _top + FillerHeaderSize;
+      } else {
+        invalidate();
+      }
+    }
+  }
+}
+
+void ParGCAllocBuffer::flush_stats(PLABStats* stats) {
+  assert(ResizePLAB, "Wasted work");
+  stats->add_allocated(_allocated);
+  stats->add_wasted(_wasted);
+  stats->add_unused(pointer_delta(_end, _top));
+}
+
+// Compute desired plab size and latch result for later
+// use. This should be called once at the end of parallel
+// scavenge; it clears the sensor accumulators.
+void PLABStats::adjust_desired_plab_sz() {
+  assert(ResizePLAB, "Not set");
+  if (_allocated == 0) {
+    assert(_unused == 0, "Inconsistency in PLAB stats");
+    _allocated = 1;
+  }
+  double wasted_frac    = (double)_unused/(double)_allocated;
+  size_t target_refills = (size_t)((wasted_frac*TargetSurvivorRatio)/
+                                   TargetPLABWastePct);
+  if (target_refills == 0) {
+    target_refills = 1;
+  }
+  _used = _allocated - _wasted - _unused;
+  size_t plab_sz = _used/(target_refills*ParallelGCThreads);
+  if (PrintPLAB) gclog_or_tty->print(" (plab_sz = %d ", plab_sz);
+  // Take historical weighted average
+  _filter.sample(plab_sz);
+  // Clip from above and below, and align to object boundary
+  plab_sz = MAX2(min_size(), (size_t)_filter.average());
+  plab_sz = MIN2(max_size(), plab_sz);
+  plab_sz = align_object_size(plab_sz);
+  // Latch the result
+  if (PrintPLAB) gclog_or_tty->print(" desired_plab_sz = %d) ", plab_sz);
+  if (ResizePLAB) {
+    _desired_plab_sz = plab_sz;
+  }
+  // Now clear the accumulators for next round:
+  // note this needs to be fixed in the case where we
+  // are retaining across scavenges. FIX ME !!! XXX
+  _allocated = 0;
+  _wasted    = 0;
+  _unused    = 0;
+}
+
+#ifndef PRODUCT
+void ParGCAllocBuffer::print() {
+  gclog_or_tty->print("parGCAllocBuffer: _bottom: %p  _top: %p  _end: %p  _hard_end: %p"
+             "_retained: %c _retained_filler: [%p,%p)\n",
+             _bottom, _top, _end, _hard_end,
+             "FT"[_retained], _retained_filler.start(), _retained_filler.end());
+}
+#endif // !PRODUCT
+
+const size_t ParGCAllocBufferWithBOT::ChunkSizeInWords =
+MIN2(CardTableModRefBS::par_chunk_heapword_alignment(),
+     ((size_t)Generation::GenGrain)/HeapWordSize);
+const size_t ParGCAllocBufferWithBOT::ChunkSizeInBytes =
+MIN2(CardTableModRefBS::par_chunk_heapword_alignment() * HeapWordSize,
+     (size_t)Generation::GenGrain);
+
+ParGCAllocBufferWithBOT::ParGCAllocBufferWithBOT(size_t word_sz,
+                                                 BlockOffsetSharedArray* bsa) :
+  ParGCAllocBuffer(word_sz),
+  _bsa(bsa),
+  _bt(bsa, MemRegion(_bottom, _hard_end)),
+  _true_end(_hard_end)
+{}
+
+// The buffer comes with its own BOT, with a shared (obviously) underlying
+// BlockOffsetSharedArray. We manipulate this BOT in the normal way
+// as we would for any contiguous space. However, on accasion we
+// need to do some buffer surgery at the extremities before we
+// start using the body of the buffer for allocations. Such surgery
+// (as explained elsewhere) is to prevent allocation on a card that
+// is in the process of being walked concurrently by another GC thread.
+// When such surgery happens at a point that is far removed (to the
+// right of the current allocation point, top), we use the "contig"
+// parameter below to directly manipulate the shared array without
+// modifying the _next_threshold state in the BOT.
+void ParGCAllocBufferWithBOT::fill_region_with_block(MemRegion mr,
+                                                     bool contig) {
+  SharedHeap::fill_region_with_object(mr);
+  if (contig) {
+    _bt.alloc_block(mr.start(), mr.end());
+  } else {
+    _bt.BlockOffsetArray::alloc_block(mr.start(), mr.end());
+  }
+}
+
+HeapWord* ParGCAllocBufferWithBOT::allocate_slow(size_t word_sz) {
+  HeapWord* res = NULL;
+  if (_true_end > _hard_end) {
+    assert((HeapWord*)align_size_down(intptr_t(_hard_end),
+                                      ChunkSizeInBytes) == _hard_end,
+           "or else _true_end should be equal to _hard_end");
+    assert(_retained, "or else _true_end should be equal to _hard_end");
+    assert(_retained_filler.end() <= _top, "INVARIANT");
+    SharedHeap::fill_region_with_object(_retained_filler);
+    if (_top < _hard_end) {
+      fill_region_with_block(MemRegion(_top, _hard_end), true);
+    }
+    HeapWord* next_hard_end = MIN2(_true_end, _hard_end + ChunkSizeInWords);
+    _retained_filler = MemRegion(_hard_end, FillerHeaderSize);
+    _bt.alloc_block(_retained_filler.start(), _retained_filler.word_size());
+    _top      = _retained_filler.end();
+    _hard_end = next_hard_end;
+    _end      = _hard_end - AlignmentReserve;
+    res       = ParGCAllocBuffer::allocate(word_sz);
+    if (res != NULL) {
+      _bt.alloc_block(res, word_sz);
+    }
+  }
+  return res;
+}
+
+void
+ParGCAllocBufferWithBOT::undo_allocation(HeapWord* obj, size_t word_sz) {
+  ParGCAllocBuffer::undo_allocation(obj, word_sz);
+  // This may back us up beyond the previous threshold, so reset.
+  _bt.set_region(MemRegion(_top, _hard_end));
+  _bt.initialize_threshold();
+}
+
+void ParGCAllocBufferWithBOT::retire(bool end_of_gc, bool retain) {
+  assert(!retain || end_of_gc, "Can only retain at GC end.");
+  if (_retained) {
+    // We're about to make the retained_filler into a block.
+    _bt.BlockOffsetArray::alloc_block(_retained_filler.start(),
+                                      _retained_filler.end());
+  }
+  // Reset _hard_end to _true_end (and update _end)
+  if (retain && _hard_end != NULL) {
+    assert(_hard_end <= _true_end, "Invariant.");
+    _hard_end = _true_end;
+    _end      = MAX2(_top, _hard_end - AlignmentReserve);
+    assert(_end <= _hard_end, "Invariant.");
+  }
+  _true_end = _hard_end;
+  HeapWord* pre_top = _top;
+
+  ParGCAllocBuffer::retire(end_of_gc, retain);
+  // Now any old _retained_filler is cut back to size, the free part is
+  // filled with a filler object, and top is past the header of that
+  // object.
+
+  if (retain && _top < _end) {
+    assert(end_of_gc && retain, "Or else retain should be false.");
+    // If the lab does not start on a card boundary, we don't want to
+    // allocate onto that card, since that might lead to concurrent
+    // allocation and card scanning, which we don't support.  So we fill
+    // the first card with a garbage object.
+    size_t first_card_index = _bsa->index_for(pre_top);
+    HeapWord* first_card_start = _bsa->address_for_index(first_card_index);
+    if (first_card_start < pre_top) {
+      HeapWord* second_card_start =
+        _bsa->address_for_index(first_card_index + 1);
+
+      // Ensure enough room to fill with the smallest block
+      second_card_start = MAX2(second_card_start, pre_top + AlignmentReserve);
+
+      // If the end is already in the first card, don't go beyond it!
+      // Or if the remainder is too small for a filler object, gobble it up.
+      if (_hard_end < second_card_start ||
+          pointer_delta(_hard_end, second_card_start) < AlignmentReserve) {
+        second_card_start = _hard_end;
+      }
+      if (pre_top < second_card_start) {
+        MemRegion first_card_suffix(pre_top, second_card_start);
+        fill_region_with_block(first_card_suffix, true);
+      }
+      pre_top = second_card_start;
+      _top = pre_top;
+      _end = MAX2(_top, _hard_end - AlignmentReserve);
+    }
+
+    // If the lab does not end on a card boundary, we don't want to
+    // allocate onto that card, since that might lead to concurrent
+    // allocation and card scanning, which we don't support.  So we fill
+    // the last card with a garbage object.
+    size_t last_card_index = _bsa->index_for(_hard_end);
+    HeapWord* last_card_start = _bsa->address_for_index(last_card_index);
+    if (last_card_start < _hard_end) {
+
+      // Ensure enough room to fill with the smallest block
+      last_card_start = MIN2(last_card_start, _hard_end - AlignmentReserve);
+
+      // If the top is already in the last card, don't go back beyond it!
+      // Or if the remainder is too small for a filler object, gobble it up.
+      if (_top > last_card_start ||
+          pointer_delta(last_card_start, _top) < AlignmentReserve) {
+        last_card_start = _top;
+      }
+      if (last_card_start < _hard_end) {
+        MemRegion last_card_prefix(last_card_start, _hard_end);
+        fill_region_with_block(last_card_prefix, false);
+      }
+      _hard_end = last_card_start;
+      _end      = MAX2(_top, _hard_end - AlignmentReserve);
+      _true_end = _hard_end;
+      assert(_end <= _hard_end, "Invariant.");
+    }
+
+    // At this point:
+    //   1) we had a filler object from the original top to hard_end.
+    //   2) We've filled in any partial cards at the front and back.
+    if (pre_top < _hard_end) {
+      // Now we can reset the _bt to do allocation in the given area.
+      MemRegion new_filler(pre_top, _hard_end);
+      fill_region_with_block(new_filler, false);
+      _top = pre_top + ParGCAllocBuffer::FillerHeaderSize;
+      // If there's no space left, don't retain.
+      if (_top >= _end) {
+        _retained = false;
+        invalidate();
+        return;
+      }
+      _retained_filler = MemRegion(pre_top, _top);
+      _bt.set_region(MemRegion(_top, _hard_end));
+      _bt.initialize_threshold();
+      assert(_bt.threshold() > _top, "initialize_threshold failed!");
+
+      // There may be other reasons for queries into the middle of the
+      // filler object.  When such queries are done in parallel with
+      // allocation, bad things can happen, if the query involves object
+      // iteration.  So we ensure that such queries do not involve object
+      // iteration, by putting another filler object on the boundaries of
+      // such queries.  One such is the object spanning a parallel card
+      // chunk boundary.
+
+      // "chunk_boundary" is the address of the first chunk boundary less
+      // than "hard_end".
+      HeapWord* chunk_boundary =
+        (HeapWord*)align_size_down(intptr_t(_hard_end-1), ChunkSizeInBytes);
+      assert(chunk_boundary < _hard_end, "Or else above did not work.");
+      assert(pointer_delta(_true_end, chunk_boundary) >= AlignmentReserve,
+             "Consequence of last card handling above.");
+
+      if (_top <= chunk_boundary) {
+        assert(_true_end == _hard_end, "Invariant.");
+        while (_top <= chunk_boundary) {
+          assert(pointer_delta(_hard_end, chunk_boundary) >= AlignmentReserve,
+                 "Consequence of last card handling above.");
+          MemRegion chunk_portion(chunk_boundary, _hard_end);
+          _bt.BlockOffsetArray::alloc_block(chunk_portion.start(),
+                                            chunk_portion.end());
+          SharedHeap::fill_region_with_object(chunk_portion);
+          _hard_end = chunk_portion.start();
+          chunk_boundary -= ChunkSizeInWords;
+        }
+        _end = _hard_end - AlignmentReserve;
+        assert(_top <= _end, "Invariant.");
+        // Now reset the initial filler chunk so it doesn't overlap with
+        // the one(s) inserted above.
+        MemRegion new_filler(pre_top, _hard_end);
+        fill_region_with_block(new_filler, false);
+      }
+    } else {
+      _retained = false;
+      invalidate();
+    }
+  } else {
+    assert(!end_of_gc ||
+           (!_retained && _true_end == _hard_end), "Checking.");
+  }
+  assert(_end <= _hard_end, "Invariant.");
+  assert(_top < _end || _top == _hard_end, "Invariant");
+}