1 /*
2 * Copyright (c) 2000, 2015, Oracle and/or its affiliates. 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_VM_MEMORY_SHAREDHEAP_HPP
26 #define SHARE_VM_MEMORY_SHAREDHEAP_HPP
27
28 #include "gc_interface/collectedHeap.hpp"
29 #include "memory/generation.hpp"
30
31 // A "SharedHeap" is an implementation of a java heap for HotSpot. This
32 // is an abstract class: there may be many different kinds of heaps. This
33 // class defines the functions that a heap must implement, and contains
34 // infrastructure common to all heaps.
35
36 class Generation;
37 class BarrierSet;
38 class GenRemSet;
39 class Space;
40 class SpaceClosure;
41 class OopClosure;
42 class OopsInGenClosure;
43 class ObjectClosure;
44 class SubTasksDone;
45 class WorkGang;
46 class FlexibleWorkGang;
47 class CollectorPolicy;
48 class KlassClosure;
49
50 // Note on use of FlexibleWorkGang's for GC.
51 // There are three places where task completion is determined.
52 // In
53 // 1) ParallelTaskTerminator::offer_termination() where _n_threads
54 // must be set to the correct value so that count of workers that
55 // have offered termination will exactly match the number
56 // working on the task. Tasks such as those derived from GCTask
57 // use ParallelTaskTerminator's. Tasks that want load balancing
58 // by work stealing use this method to gauge completion.
59 // 2) SubTasksDone has a variable _n_threads that is used in
60 // all_tasks_completed() to determine completion. all_tasks_complete()
61 // counts the number of tasks that have been done and then reset
62 // the SubTasksDone so that it can be used again. When the number of
63 // tasks is set to the number of GC workers, then _n_threads must
64 // be set to the number of active GC workers. G1RootProcessor and
65 // GenCollectedHeap have SubTasksDone.
66 // 3) SequentialSubTasksDone has an _n_threads that is used in
67 // a way similar to SubTasksDone and has the same dependency on the
68 // number of active GC workers. CompactibleFreeListSpace and Space
69 // have SequentialSubTasksDone's.
70 //
71 // Examples of using SubTasksDone and SequentialSubTasksDone:
72 // G1RootProcessor and GenCollectedHeap::process_roots() use
73 // SubTasksDone* _process_strong_tasks to claim tasks for workers
74 //
75 // GenCollectedHeap::gen_process_roots() calls
76 // rem_set()->younger_refs_iterate()
77 // to scan the card table and which eventually calls down into
78 // CardTableModRefBS::par_non_clean_card_iterate_work(). This method
79 // uses SequentialSubTasksDone* _pst to claim tasks.
80 // Both SubTasksDone and SequentialSubTasksDone call their method
81 // all_tasks_completed() to count the number of GC workers that have
82 // finished their work. That logic is "when all the workers are
83 // finished the tasks are finished".
84 //
85 // The pattern that appears in the code is to set _n_threads
86 // to a value > 1 before a task that you would like executed in parallel
87 // and then to set it to 0 after that task has completed. A value of
88 // 0 is a "special" value in set_n_threads() which translates to
89 // setting _n_threads to 1.
90 //
91 // Some code uses _n_termination to decide if work should be done in
92 // parallel. The notorious possibly_parallel_oops_do() in threads.cpp
93 // is an example of such code. Look for variable "is_par" for other
94 // examples.
95 //
96 // The active_workers is not reset to 0 after a parallel phase. It's
97 // value may be used in later phases and in one instance at least
98 // (the parallel remark) it has to be used (the parallel remark depends
99 // on the partitioning done in the previous parallel scavenge).
100
101 class SharedHeap : public CollectedHeap {
102 friend class VMStructs;
103
104 friend class VM_GC_Operation;
105 friend class VM_CGC_Operation;
106
107 protected:
108 // There should be only a single instance of "SharedHeap" in a program.
109 // This is enforced with the protected constructor below, which will also
110 // set the static pointer "_sh" to that instance.
111 static SharedHeap* _sh;
112
113 // If we're doing parallel GC, use this gang of threads.
114 FlexibleWorkGang* _workers;
115
116 // Full initialization is done in a concrete subtype's "initialize"
117 // function.
118 SharedHeap();
119
120 // Returns true if the calling thread holds the heap lock,
121 // or the calling thread is a par gc thread and the heap_lock is held
122 // by the vm thread doing a gc operation.
123 bool heap_lock_held_for_gc();
124 // True if the heap_lock is held by the a non-gc thread invoking a gc
125 // operation.
126 bool _thread_holds_heap_lock_for_gc;
127
128 public:
129 static SharedHeap* heap() { return _sh; }
130
131 void set_barrier_set(BarrierSet* bs);
132
133 // Does operations required after initialization has been done.
134 virtual void post_initialize();
135
136 // Initialization of ("weak") reference processing support
137 virtual void ref_processing_init();
138
139 // Iteration functions.
140 void oop_iterate(ExtendedOopClosure* cl) = 0;
141
142 // Iterate over all spaces in use in the heap, in an undefined order.
143 virtual void space_iterate(SpaceClosure* cl) = 0;
144
145 // A SharedHeap will contain some number of spaces. This finds the
146 // space whose reserved area contains the given address, or else returns
147 // NULL.
148 virtual Space* space_containing(const void* addr) const = 0;
149
150 bool no_gc_in_progress() { return !is_gc_active(); }
151
152 // Note, the below comment needs to be updated to reflect the changes
153 // introduced by JDK-8076225. This should be done as part of JDK-8076289.
154 //
155 //Some collectors will perform "process_strong_roots" in parallel.
156 // Such a call will involve claiming some fine-grained tasks, such as
157 // scanning of threads. To make this process simpler, we provide the
158 // "strong_roots_parity()" method. Collectors that start parallel tasks
159 // whose threads invoke "process_strong_roots" must
160 // call "change_strong_roots_parity" in sequential code starting such a
161 // task. (This also means that a parallel thread may only call
162 // process_strong_roots once.)
163 //
164 // For calls to process_roots by sequential code, the parity is
165 // updated automatically.
166 //
167 // The idea is that objects representing fine-grained tasks, such as
168 // threads, will contain a "parity" field. A task will is claimed in the
169 // current "process_roots" call only if its parity field is the
170 // same as the "strong_roots_parity"; task claiming is accomplished by
171 // updating the parity field to the strong_roots_parity with a CAS.
172 //
173 // If the client meats this spec, then strong_roots_parity() will have
174 // the following properties:
175 // a) to return a different value than was returned before the last
176 // call to change_strong_roots_parity, and
177 // c) to never return a distinguished value (zero) with which such
178 // task-claiming variables may be initialized, to indicate "never
179 // claimed".
180 public:
181
182 // Call these in sequential code around process_roots.
183 // strong_roots_prologue calls change_strong_roots_parity, if
184 // parallel tasks are enabled.
185 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
186 SharedHeap* _sh;
187
188 public:
189 StrongRootsScope(SharedHeap* heap, bool activate = true);
190 ~StrongRootsScope();
191 };
192
193 private:
194
195 public:
196 FlexibleWorkGang* workers() const { return _workers; }
197
198 // The functions below are helper functions that a subclass of
199 // "SharedHeap" can use in the implementation of its virtual
200 // functions.
201
202 public:
203
204 // Do anything common to GC's.
205 virtual void gc_prologue(bool full) = 0;
206 virtual void gc_epilogue(bool full) = 0;
207
208 // Sets the number of parallel threads that will be doing tasks
209 // (such as process roots) subsequently.
210 virtual void set_par_threads(uint t);
211 };
212
213 #endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP