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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. G1CollectedHeap,
65 // HRInto_G1RemSet, GenCollectedHeap and SharedHeap have SubTasksDone.
66 // This seems too many.
67 // 3) SequentialSubTasksDone has an _n_threads that is used in
68 // a way similar to SubTasksDone and has the same dependency on the
69 // number of active GC workers. CompactibleFreeListSpace and Space
70 // have SequentialSubTasksDone's.
71 // Example of using SubTasksDone and SequentialSubTasksDone
72 // G1CollectedHeap::g1_process_roots()
73 // to SharedHeap::process_roots() and uses
74 // SubTasksDone* _process_strong_tasks to claim tasks.
75 // 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_terminiation 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 private:
108 // For claiming strong_roots tasks.
109 SubTasksDone* _process_strong_tasks;
110
111 protected:
112 // There should be only a single instance of "SharedHeap" in a program.
113 // This is enforced with the protected constructor below, which will also
114 // set the static pointer "_sh" to that instance.
115 static SharedHeap* _sh;
116
117 // and the Gen Remembered Set, at least one good enough to scan the perm
118 // gen.
119 GenRemSet* _rem_set;
120
121 // A gc policy, controls global gc resource issues
122 CollectorPolicy *_collector_policy;
123
124 // See the discussion below, in the specification of the reader function
125 // for this variable.
126 int _strong_roots_parity;
127
128 // If we're doing parallel GC, use this gang of threads.
129 FlexibleWorkGang* _workers;
130
131 // Full initialization is done in a concrete subtype's "initialize"
132 // function.
133 SharedHeap(CollectorPolicy* policy_);
134
135 // Returns true if the calling thread holds the heap lock,
136 // or the calling thread is a par gc thread and the heap_lock is held
137 // by the vm thread doing a gc operation.
138 bool heap_lock_held_for_gc();
139 // True if the heap_lock is held by the a non-gc thread invoking a gc
140 // operation.
141 bool _thread_holds_heap_lock_for_gc;
142
143 public:
144 static SharedHeap* heap() { return _sh; }
145
146 void set_barrier_set(BarrierSet* bs);
147 SubTasksDone* process_strong_tasks() { return _process_strong_tasks; }
148
149 // Does operations required after initialization has been done.
150 virtual void post_initialize();
151
152 // Initialization of ("weak") reference processing support
153 virtual void ref_processing_init();
154
155 // This function returns the "GenRemSet" object that allows us to scan
156 // generations in a fully generational heap.
157 GenRemSet* rem_set() { return _rem_set; }
158
159 // Iteration functions.
160 void oop_iterate(ExtendedOopClosure* cl) = 0;
161
162 // Iterate over all spaces in use in the heap, in an undefined order.
163 virtual void space_iterate(SpaceClosure* cl) = 0;
164
165 // A SharedHeap will contain some number of spaces. This finds the
166 // space whose reserved area contains the given address, or else returns
167 // NULL.
168 virtual Space* space_containing(const void* addr) const = 0;
169
170 bool no_gc_in_progress() { return !is_gc_active(); }
171
172 // Some collectors will perform "process_strong_roots" in parallel.
173 // Such a call will involve claiming some fine-grained tasks, such as
174 // scanning of threads. To make this process simpler, we provide the
175 // "strong_roots_parity()" method. Collectors that start parallel tasks
176 // whose threads invoke "process_strong_roots" must
177 // call "change_strong_roots_parity" in sequential code starting such a
178 // task. (This also means that a parallel thread may only call
179 // process_strong_roots once.)
180 //
181 // For calls to process_roots by sequential code, the parity is
182 // updated automatically.
183 //
184 // The idea is that objects representing fine-grained tasks, such as
185 // threads, will contain a "parity" field. A task will is claimed in the
186 // current "process_roots" call only if its parity field is the
187 // same as the "strong_roots_parity"; task claiming is accomplished by
188 // updating the parity field to the strong_roots_parity with a CAS.
189 //
190 // If the client meats this spec, then strong_roots_parity() will have
191 // the following properties:
192 // a) to return a different value than was returned before the last
193 // call to change_strong_roots_parity, and
194 // c) to never return a distinguished value (zero) with which such
195 // task-claiming variables may be initialized, to indicate "never
196 // claimed".
197 public:
198 int strong_roots_parity() { return _strong_roots_parity; }
199
200 // Call these in sequential code around process_roots.
201 // strong_roots_prologue calls change_strong_roots_parity, if
202 // parallel tasks are enabled.
203 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
204 // Used to implement the Thread work barrier.
205 static Monitor* _lock;
206
207 SharedHeap* _sh;
208 volatile jint _n_workers_done_with_threads;
209
210 public:
211 StrongRootsScope(SharedHeap* heap, bool activate = true);
212 ~StrongRootsScope();
213
214 // Mark that this thread is done with the Threads work.
215 void mark_worker_done_with_threads(uint n_workers);
216 // Wait until all n_workers are done with the Threads work.
217 void wait_until_all_workers_done_with_threads(uint n_workers);
218 };
219 friend class StrongRootsScope;
220
221 // The current active StrongRootScope
222 StrongRootsScope* _strong_roots_scope;
223
224 StrongRootsScope* active_strong_roots_scope() const;
225
226 private:
227 void register_strong_roots_scope(StrongRootsScope* scope);
228 void unregister_strong_roots_scope(StrongRootsScope* scope);
229 void change_strong_roots_parity();
230
231 public:
232 enum ScanningOption {
233 SO_None = 0x0,
234 SO_AllCodeCache = 0x8,
235 SO_ScavengeCodeCache = 0x10
236 };
237
238 FlexibleWorkGang* workers() const { return _workers; }
239
240 // Invoke the "do_oop" method the closure "roots" on all root locations.
241 // The "so" argument determines which roots the closure is applied to:
242 // "SO_None" does none;
243 // "SO_AllCodeCache" applies the closure to all elements of the CodeCache.
244 // "SO_ScavengeCodeCache" applies the closure to elements on the scavenge root list in the CodeCache.
245 void process_roots(bool activate_scope,
246 ScanningOption so,
247 OopClosure* strong_roots,
248 OopClosure* weak_roots,
249 CLDClosure* strong_cld_closure,
250 CLDClosure* weak_cld_closure,
251 CodeBlobClosure* code_roots);
252 void process_all_roots(bool activate_scope,
253 ScanningOption so,
254 OopClosure* roots,
255 CLDClosure* cld_closure,
256 CodeBlobClosure* code_roots);
257 void process_strong_roots(bool activate_scope,
258 ScanningOption so,
259 OopClosure* roots,
260 CLDClosure* cld_closure,
261 CodeBlobClosure* code_roots);
262
263
264 // Apply "root_closure" to the JNI weak roots..
265 void process_weak_roots(OopClosure* root_closure);
266
267 // The functions below are helper functions that a subclass of
268 // "SharedHeap" can use in the implementation of its virtual
269 // functions.
270
271 public:
272
273 // Do anything common to GC's.
274 virtual void gc_prologue(bool full) = 0;
275 virtual void gc_epilogue(bool full) = 0;
276
277 // Sets the number of parallel threads that will be doing tasks
278 // (such as process roots) subsequently.
279 virtual void set_par_threads(uint t);
280
281 int n_termination();
282 void set_n_termination(int t);
283
284 //
285 // New methods from CollectedHeap
286 //
287
288 // Some utilities.
289 void print_size_transition(outputStream* out,
290 size_t bytes_before,
291 size_t bytes_after,
292 size_t capacity);
293 };
294
295 inline SharedHeap::ScanningOption operator|(SharedHeap::ScanningOption so0, SharedHeap::ScanningOption so1) {
296 return static_cast<SharedHeap::ScanningOption>(static_cast<int>(so0) | static_cast<int>(so1));
297 }
298
299 #endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP