1 /*
2 * Copyright (c) 2000, 2014, 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 class GCPhaseTimeTracker;
50
51 // Note on use of FlexibleWorkGang's for GC.
52 // There are three places where task completion is determined.
53 // In
54 // 1) ParallelTaskTerminator::offer_termination() where _n_threads
55 // must be set to the correct value so that count of workers that
56 // have offered termination will exactly match the number
57 // working on the task. Tasks such as those derived from GCTask
58 // use ParallelTaskTerminator's. Tasks that want load balancing
59 // by work stealing use this method to gauge completion.
60 // 2) SubTasksDone has a variable _n_threads that is used in
61 // all_tasks_completed() to determine completion. all_tasks_complete()
62 // counts the number of tasks that have been done and then reset
63 // the SubTasksDone so that it can be used again. When the number of
64 // tasks is set to the number of GC workers, then _n_threads must
65 // be set to the number of active GC workers. G1CollectedHeap,
66 // HRInto_G1RemSet, GenCollectedHeap and SharedHeap have SubTasksDone.
67 // This seems too many.
68 // 3) SequentialSubTasksDone has an _n_threads that is used in
69 // a way similar to SubTasksDone and has the same dependency on the
70 // number of active GC workers. CompactibleFreeListSpace and Space
71 // have SequentialSubTasksDone's.
72 // Example of using SubTasksDone and SequentialSubTasksDone
73 // G1CollectedHeap::g1_process_roots()
74 // to SharedHeap::process_roots() and uses
75 // SubTasksDone* _process_strong_tasks to claim tasks.
76 // process_roots() calls
77 // rem_set()->younger_refs_iterate()
78 // to scan the card table and which eventually calls down into
79 // CardTableModRefBS::par_non_clean_card_iterate_work(). This method
80 // uses SequentialSubTasksDone* _pst to claim tasks.
81 // Both SubTasksDone and SequentialSubTasksDone call their method
82 // all_tasks_completed() to count the number of GC workers that have
83 // finished their work. That logic is "when all the workers are
84 // finished the tasks are finished".
85 //
86 // The pattern that appears in the code is to set _n_threads
87 // to a value > 1 before a task that you would like executed in parallel
88 // and then to set it to 0 after that task has completed. A value of
89 // 0 is a "special" value in set_n_threads() which translates to
90 // setting _n_threads to 1.
91 //
92 // Some code uses _n_termination to decide if work should be done in
93 // parallel. The notorious possibly_parallel_oops_do() in threads.cpp
94 // is an example of such code. Look for variable "is_par" for other
95 // examples.
96 //
97 // The active_workers is not reset to 0 after a parallel phase. It's
98 // value may be used in later phases and in one instance at least
99 // (the parallel remark) it has to be used (the parallel remark depends
100 // on the partitioning done in the previous parallel scavenge).
101
102 class SharedHeap : public CollectedHeap {
103 friend class VMStructs;
104
105 friend class VM_GC_Operation;
106 friend class VM_CGC_Operation;
107 public:
108 // The set of potentially parallel tasks in root scanning.
109 enum SH_process_roots_tasks {
110 SH_PS_Threads_oops_do,
111 SH_PS_StringTable_oops_do,
112 SH_PS_Universe_oops_do,
113 SH_PS_JNIHandles_oops_do,
114 SH_PS_ObjectSynchronizer_oops_do,
115 SH_PS_FlatProfiler_oops_do,
116 SH_PS_Management_oops_do,
117 SH_PS_SystemDictionary_oops_do,
118 SH_PS_ClassLoaderDataGraph_oops_do,
119 SH_PS_jvmti_oops_do,
120 SH_PS_CodeCache_oops_do,
121 // Leave this one last.
122 SH_PS_NumElements
123 };
124
125 static const char* ext_roots_task_str(uint task);
126 private:
127 // For claiming strong_roots tasks.
128 SubTasksDone* _process_strong_tasks;
129
130 protected:
131 // There should be only a single instance of "SharedHeap" in a program.
132 // This is enforced with the protected constructor below, which will also
133 // set the static pointer "_sh" to that instance.
134 static SharedHeap* _sh;
135
136 // A gc policy, controls global gc resource issues
137 CollectorPolicy *_collector_policy;
138
139 // See the discussion below, in the specification of the reader function
140 // for this variable.
141 int _strong_roots_parity;
142
143 // If we're doing parallel GC, use this gang of threads.
144 FlexibleWorkGang* _workers;
145
146 // Full initialization is done in a concrete subtype's "initialize"
147 // function.
148 SharedHeap(CollectorPolicy* policy_);
149
150 // Returns true if the calling thread holds the heap lock,
151 // or the calling thread is a par gc thread and the heap_lock is held
152 // by the vm thread doing a gc operation.
153 bool heap_lock_held_for_gc();
154 // True if the heap_lock is held by the a non-gc thread invoking a gc
155 // operation.
156 bool _thread_holds_heap_lock_for_gc;
157
158 public:
159 static SharedHeap* heap() { return _sh; }
160
161 void set_barrier_set(BarrierSet* bs);
162 SubTasksDone* process_strong_tasks() { return _process_strong_tasks; }
163
164 // Does operations required after initialization has been done.
165 virtual void post_initialize();
166
167 // Initialization of ("weak") reference processing support
168 virtual void ref_processing_init();
169
170 // Iteration functions.
171 void oop_iterate(ExtendedOopClosure* cl) = 0;
172
173 // Iterate over all spaces in use in the heap, in an undefined order.
174 virtual void space_iterate(SpaceClosure* cl) = 0;
175
176 // A SharedHeap will contain some number of spaces. This finds the
177 // space whose reserved area contains the given address, or else returns
178 // NULL.
179 virtual Space* space_containing(const void* addr) const = 0;
180
181 bool no_gc_in_progress() { return !is_gc_active(); }
182
183 // Some collectors will perform "process_strong_roots" in parallel.
184 // Such a call will involve claiming some fine-grained tasks, such as
185 // scanning of threads. To make this process simpler, we provide the
186 // "strong_roots_parity()" method. Collectors that start parallel tasks
187 // whose threads invoke "process_strong_roots" must
188 // call "change_strong_roots_parity" in sequential code starting such a
189 // task. (This also means that a parallel thread may only call
190 // process_strong_roots once.)
191 //
192 // For calls to process_roots by sequential code, the parity is
193 // updated automatically.
194 //
195 // The idea is that objects representing fine-grained tasks, such as
196 // threads, will contain a "parity" field. A task will is claimed in the
197 // current "process_roots" call only if its parity field is the
198 // same as the "strong_roots_parity"; task claiming is accomplished by
199 // updating the parity field to the strong_roots_parity with a CAS.
200 //
201 // If the client meats this spec, then strong_roots_parity() will have
202 // the following properties:
203 // a) to return a different value than was returned before the last
204 // call to change_strong_roots_parity, and
205 // c) to never return a distinguished value (zero) with which such
206 // task-claiming variables may be initialized, to indicate "never
207 // claimed".
208 public:
209 int strong_roots_parity() { return _strong_roots_parity; }
210
211 // Call these in sequential code around process_roots.
212 // strong_roots_prologue calls change_strong_roots_parity, if
213 // parallel tasks are enabled.
214 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
215 // Used to implement the Thread work barrier.
216 static Monitor* _lock;
217
218 SharedHeap* _sh;
219 volatile jint _n_workers_done_with_threads;
220
221 public:
222 StrongRootsScope(SharedHeap* heap, bool activate = true);
223 ~StrongRootsScope();
224
225 // Mark that this thread is done with the Threads work.
226 void mark_worker_done_with_threads(uint n_workers);
227 // Wait until all n_workers are done with the Threads work.
228 void wait_until_all_workers_done_with_threads(uint n_workers);
229 };
230 friend class StrongRootsScope;
231
232 // The current active StrongRootScope
233 StrongRootsScope* _strong_roots_scope;
234
235 StrongRootsScope* active_strong_roots_scope() const;
236
237 private:
238 void register_strong_roots_scope(StrongRootsScope* scope);
239 void unregister_strong_roots_scope(StrongRootsScope* scope);
240 void change_strong_roots_parity();
241
242 public:
243 enum ScanningOption {
244 SO_None = 0x0,
245 SO_AllCodeCache = 0x8,
246 SO_ScavengeCodeCache = 0x10
247 };
248
249 FlexibleWorkGang* workers() const { return _workers; }
250
251 // Invoke the "do_oop" method the closure "roots" on all root locations.
252 // The "so" argument determines which roots the closure is applied to:
253 // "SO_None" does none;
254 // "SO_AllCodeCache" applies the closure to all elements of the CodeCache.
255 // "SO_ScavengeCodeCache" applies the closure to elements on the scavenge root list in the CodeCache.
256 void process_roots(bool activate_scope,
257 ScanningOption so,
258 OopClosure* strong_roots,
259 OopClosure* weak_roots,
260 CLDClosure* strong_cld_closure,
261 CLDClosure* weak_cld_closure,
262 CodeBlobClosure* code_roots,
263 GCPhaseTimeTracker* phase_durations = NULL);
264 void process_all_roots(bool activate_scope,
265 ScanningOption so,
266 OopClosure* roots,
267 CLDClosure* cld_closure,
268 CodeBlobClosure* code_roots,
269 GCPhaseTimeTracker* phase_durations = NULL);
270 void process_strong_roots(bool activate_scope,
271 ScanningOption so,
272 OopClosure* roots,
273 CLDClosure* cld_closure,
274 CodeBlobClosure* code_roots,
275 GCPhaseTimeTracker* phase_durations = NULL);
276
277
278 // Apply "root_closure" to the JNI weak roots..
279 void process_weak_roots(OopClosure* root_closure);
280
281 // The functions below are helper functions that a subclass of
282 // "SharedHeap" can use in the implementation of its virtual
283 // functions.
284
285 public:
286
287 // Do anything common to GC's.
288 virtual void gc_prologue(bool full) = 0;
289 virtual void gc_epilogue(bool full) = 0;
290
291 // Sets the number of parallel threads that will be doing tasks
292 // (such as process roots) subsequently.
293 virtual void set_par_threads(uint t);
294
295 int n_termination();
296 void set_n_termination(int t);
297
298 //
299 // New methods from CollectedHeap
300 //
301
302 // Some utilities.
303 void print_size_transition(outputStream* out,
304 size_t bytes_before,
305 size_t bytes_after,
306 size_t capacity);
307 };
308
309 inline SharedHeap::ScanningOption operator|(SharedHeap::ScanningOption so0, SharedHeap::ScanningOption so1) {
310 return static_cast<SharedHeap::ScanningOption>(static_cast<int>(so0) | static_cast<int>(so1));
311 }
312
313 #endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP