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/shared/gcTimer.hpp"

    28 #include "gc/shenandoah/shenandoahHeap.hpp"

    29 #include "gc/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 ShenandoahMarkCompact : public CHeapObj<mtGC> {

    53 private:

    54   GCTimer* _gc_timer;

    55 

    56 public:

    57   void initialize(GCTimer* gc_timer);

    58   void do_it(GCCause::Cause gc_cause);

    59 

    60 private:

    61   void phase1_mark_heap();

    62   void phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices);

    63   void phase3_update_references();

    64   void phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices);

    65 

    66   void calculate_target_humongous_objects();

    67   void compact_humongous_objects();

    68 

    69 };

    70 

    71 #endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHMARKCOMPACT_HPP