1 /*
 2  * Copyright (c) 2014, 2021, Red Hat, Inc. All rights reserved.
 3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 4  *
 5  * This code is free software; you can redistribute it and/or modify it
 6  * under the terms of the GNU General Public License version 2 only, as
 7  * published by the Free Software Foundation.
 8  *
 9  * This code is distributed in the hope that it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12  * version 2 for more details (a copy is included in the LICENSE file that
13  * accompanied this code).
14  *
15  * You should have received a copy of the GNU General Public License version
16  * 2 along with this work; if not, write to the Free Software Foundation,
17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18  *
19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20  * or visit www.oracle.com if you need additional information or have any
21  * questions.
22  *
23  */
24 
25 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHFULLGC_HPP
26 #define SHARE_GC_SHENANDOAH_SHENANDOAHFULLGC_HPP
27 
28 #include "gc/shared/gcTimer.hpp"
29 #include "gc/shenandoah/shenandoahGC.hpp"
30 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
31 
32 /**
33  * This implements Full GC (e.g. when invoking System.gc()) using a mark-compact algorithm.
34  *
35  * Current implementation is parallel sliding Lisp-2-style algorithm, based on
36  * "Parallel Garbage Collection for Shared Memory Multiprocessors", by Christine Flood et al.
37  * http://people.csail.mit.edu/shanir/publications/dfsz2001.pdf
38  *
39  * It is implemented in four phases:
40  *
41  * 1. Mark all live objects of the heap by traversing objects starting at GC roots.
42  * 2. Calculate the new location of each live object. This is done by sequentially scanning
43  *    the heap, keeping track of a next-location-pointer, which is then written to each
44  *    object's fwdptr field.
45  * 3. Update all references. This is implemented by another scan of the heap, and updates
46  *    all references in live objects by what's stored in the target object's fwdptr.
47  * 4. Compact the heap by copying all live objects to their new location.
48  *
49  * Parallelization is handled by assigning each GC worker the slice of the heap (the set of regions)
50  * where it does sliding compaction, without interfering with other threads.
51  */
52 
53 class PreservedMarksSet;
54 class VM_ShenandoahFullGC;
55 class ShenandoahDegenGC;
56 
57 class ShenandoahFullGC : public ShenandoahGC {
58   template <bool ALT_FWD>
59   friend class ShenandoahPrepareForCompactionObjectClosure;
60   friend class VM_ShenandoahFullGC;
61   friend class ShenandoahDegenGC;
62 
63 private:
64   GCTimer* _gc_timer;
65 
66   PreservedMarksSet* _preserved_marks;
67 
68 public:
69   ShenandoahFullGC();
70   ~ShenandoahFullGC();
71   bool collect(GCCause::Cause cause);
72 
73 private:
74   // GC entries
75   void vmop_entry_full(GCCause::Cause cause);
76   void entry_full(GCCause::Cause cause);
77   void op_full(GCCause::Cause cause);
78 
79   void do_it(GCCause::Cause gc_cause);
80 
81   void phase1_mark_heap();
82   void phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices);
83   void phase3_update_references();
84   void phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices);
85 
86   void distribute_slices(ShenandoahHeapRegionSet** worker_slices);
87   template <bool ALT_FWD>
88   void calculate_target_humongous_objects_impl();
89   void calculate_target_humongous_objects();
90   template <bool ALT_FWD>
91   void compact_humongous_objects_impl();
92   void compact_humongous_objects();
93 };
94 
95 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHFULLGC_HPP