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_strong_roots() calls
73 // process_strong_roots(false, // no scoping; this is parallel code
74 // is_scavenging, so,
75 // &buf_scan_non_heap_roots,
76 // &eager_scan_code_roots);
77 // which delegates to SharedHeap::process_strong_roots() and uses
78 // SubTasksDone* _process_strong_tasks to claim tasks.
79 // process_strong_roots() calls
80 // rem_set()->younger_refs_iterate()
81 // to scan the card table and which eventually calls down into
82 // CardTableModRefBS::par_non_clean_card_iterate_work(). This method
83 // uses SequentialSubTasksDone* _pst to claim tasks.
84 // Both SubTasksDone and SequentialSubTasksDone call their method
85 // all_tasks_completed() to count the number of GC workers that have
86 // finished their work. That logic is "when all the workers are
87 // finished the tasks are finished".
88 //
89 // The pattern that appears in the code is to set _n_threads
90 // to a value > 1 before a task that you would like executed in parallel
91 // and then to set it to 0 after that task has completed. A value of
92 // 0 is a "special" value in set_n_threads() which translates to
93 // setting _n_threads to 1.
94 //
95 // Some code uses _n_termination to decide if work should be done in
96 // parallel. The notorious possibly_parallel_oops_do() in threads.cpp
97 // is an example of such code. Look for variable "is_par" for other
98 // examples.
99 //
165
166 // Iterate over all spaces in use in the heap, in an undefined order.
167 virtual void space_iterate(SpaceClosure* cl) = 0;
168
169 // A SharedHeap will contain some number of spaces. This finds the
170 // space whose reserved area contains the given address, or else returns
171 // NULL.
172 virtual Space* space_containing(const void* addr) const = 0;
173
174 bool no_gc_in_progress() { return !is_gc_active(); }
175
176 // Some collectors will perform "process_strong_roots" in parallel.
177 // Such a call will involve claiming some fine-grained tasks, such as
178 // scanning of threads. To make this process simpler, we provide the
179 // "strong_roots_parity()" method. Collectors that start parallel tasks
180 // whose threads invoke "process_strong_roots" must
181 // call "change_strong_roots_parity" in sequential code starting such a
182 // task. (This also means that a parallel thread may only call
183 // process_strong_roots once.)
184 //
185 // For calls to process_strong_roots by sequential code, the parity is
186 // updated automatically.
187 //
188 // The idea is that objects representing fine-grained tasks, such as
189 // threads, will contain a "parity" field. A task will is claimed in the
190 // current "process_strong_roots" call only if its parity field is the
191 // same as the "strong_roots_parity"; task claiming is accomplished by
192 // updating the parity field to the strong_roots_parity with a CAS.
193 //
194 // If the client meats this spec, then strong_roots_parity() will have
195 // the following properties:
196 // a) to return a different value than was returned before the last
197 // call to change_strong_roots_parity, and
198 // c) to never return a distinguished value (zero) with which such
199 // task-claiming variables may be initialized, to indicate "never
200 // claimed".
201 private:
202 void change_strong_roots_parity();
203 public:
204 int strong_roots_parity() { return _strong_roots_parity; }
205
206 // Call these in sequential code around process_strong_roots.
207 // strong_roots_prologue calls change_strong_roots_parity, if
208 // parallel tasks are enabled.
209 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
210 public:
211 StrongRootsScope(SharedHeap* outer, bool activate = true);
212 ~StrongRootsScope();
213 };
214 friend class StrongRootsScope;
215
216 enum ScanningOption {
217 SO_None = 0x0,
218 SO_AllClasses = 0x1,
219 SO_SystemClasses = 0x2,
220 SO_Strings = 0x4,
221 SO_AllCodeCache = 0x8,
222 SO_ScavengeCodeCache = 0x10
223 };
224
225 FlexibleWorkGang* workers() const { return _workers; }
226
227 // Invoke the "do_oop" method the closure "roots" on all root locations.
228 // The "so" argument determines which roots the closure is applied to:
229 // "SO_None" does none;
230 // "SO_AllClasses" applies the closure to all entries in the SystemDictionary;
231 // "SO_SystemClasses" to all the "system" classes and loaders;
232 // "SO_Strings" applies the closure to all entries in StringTable;
233 // "SO_AllCodeCache" applies the closure to all elements of the CodeCache.
234 // "SO_ScavengeCodeCache" applies the closure to elements on the scavenge root list in the CodeCache.
235 void process_strong_roots(bool activate_scope,
236 ScanningOption so,
237 OopClosure* roots,
238 KlassClosure* klass_closure);
239
240 // Apply "root_closure" to the JNI weak roots..
241 void process_weak_roots(OopClosure* root_closure);
242
243 // The functions below are helper functions that a subclass of
244 // "SharedHeap" can use in the implementation of its virtual
245 // functions.
246
247 public:
248
249 // Do anything common to GC's.
250 virtual void gc_prologue(bool full) = 0;
251 virtual void gc_epilogue(bool full) = 0;
252
253 // Sets the number of parallel threads that will be doing tasks
254 // (such as process strong roots) subsequently.
255 virtual void set_par_threads(uint t);
256
257 int n_termination();
258 void set_n_termination(int t);
259
260 //
261 // New methods from CollectedHeap
262 //
263
264 // Some utilities.
265 void print_size_transition(outputStream* out,
266 size_t bytes_before,
267 size_t bytes_after,
268 size_t capacity);
269 };
270
271 inline SharedHeap::ScanningOption operator|(SharedHeap::ScanningOption so0, SharedHeap::ScanningOption so1) {
272 return static_cast<SharedHeap::ScanningOption>(static_cast<int>(so0) | static_cast<int>(so1));
273 }
274
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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_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 //
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
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