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