1 /*
   2  * Copyright (c) 2014, 2018, Red Hat, Inc. All rights reserved.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.
   7  *
   8  * This code is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  11  * version 2 for more details (a copy is included in the LICENSE file that
  12  * accompanied this code).
  13  *
  14  * You should have received a copy of the GNU General Public License version
  15  * 2 along with this work; if not, write to the Free Software Foundation,
  16  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  17  *
  18  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  19  * or visit www.oracle.com if you need additional information or have any
  20  * questions.
  21  *
  22  */
  23 
  24 #ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHMARKCOMPACT_HPP
  25 #define SHARE_VM_GC_SHENANDOAH_SHENANDOAHMARKCOMPACT_HPP
  26 
  27 #include "gc_implementation/shared/gcTimer.hpp"
  28 #include "gc_implementation/shenandoah/shenandoahHeap.hpp"
  29 #include "gc_implementation/shenandoah/shenandoahHeapRegionSet.hpp"
  30 
  31 /**
  32  * This implements Full GC (e.g. when invoking System.gc()) using a mark-compact algorithm.
  33  *
  34  * Current implementation is parallel sliding Lisp-2-style algorithm, based on
  35  * "Parallel Garbage Collection for Shared Memory Multiprocessors", by Christine Flood et al.
  36  * http://people.csail.mit.edu/shanir/publications/dfsz2001.pdf
  37  *
  38  * It is implemented in four phases:
  39  *
  40  * 1. Mark all live objects of the heap by traversing objects starting at GC roots.
  41  * 2. Calculate the new location of each live object. This is done by sequentially scanning
  42  *    the heap, keeping track of a next-location-pointer, which is then written to each
  43  *    object's fwdptr field.
  44  * 3. Update all references. This is implemented by another scan of the heap, and updates
  45  *    all references in live objects by what's stored in the target object's fwdptr.
  46  * 4. Compact the heap by copying all live objects to their new location.
  47  *
  48  * Parallelization is handled by assigning each GC worker the slice of the heap (the set of regions)
  49  * where it does sliding compaction, without interfering with other threads.
  50  */
  51 
  52 class PreservedMarksSet;
  53 
  54 class ShenandoahMarkCompact : public CHeapObj<mtGC> {
  55   friend class ShenandoahPrepareForCompactionObjectClosure;
  56 private:
  57   GCTimer* _gc_timer;
  58 
  59   PreservedMarksSet* _preserved_marks;
  60 
  61 public:
  62   ShenandoahMarkCompact();
  63   void initialize(GCTimer* gc_timer);
  64 
  65   void do_it(GCCause::Cause gc_cause);
  66 
  67 private:
  68   void phase1_mark_heap();
  69   void phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices);
  70   void phase3_update_references();
  71   void phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices);
  72 
  73   void distribute_slices(ShenandoahHeapRegionSet** worker_slices);
  74   void calculate_target_humongous_objects();
  75   void compact_humongous_objects();
  76 };
  77 
  78 #endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHMARKCOMPACT_HPP