1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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_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 public:
107 // The set of potentially parallel tasks in root scanning.
108 enum SH_process_roots_tasks {
109 SH_PS_Threads_oops_do,
110 SH_PS_StringTable_oops_do,
111 SH_PS_Universe_oops_do,
112 SH_PS_JNIHandles_oops_do,
113 SH_PS_ObjectSynchronizer_oops_do,
114 SH_PS_FlatProfiler_oops_do,
115 SH_PS_Management_oops_do,
116 SH_PS_SystemDictionary_oops_do,
117 SH_PS_ClassLoaderDataGraph_oops_do,
118 SH_PS_jvmti_oops_do,
119 SH_PS_CodeCache_oops_do,
120 // Leave this one last.
121 SH_PS_NumElements
122 };
123
124 static const char* ext_roots_task_str(uint task);
125 private:
126 // For claiming strong_roots tasks.
127 SubTasksDone* _process_strong_tasks;
128
129 protected:
130 // There should be only a single instance of "SharedHeap" in a program.
131 // This is enforced with the protected constructor below, which will also
132 // set the static pointer "_sh" to that instance.
133 static SharedHeap* _sh;
134
135 // A gc policy, controls global gc resource issues
136 CollectorPolicy *_collector_policy;
137
138 // See the discussion below, in the specification of the reader function
139 // for this variable.
140 int _strong_roots_parity;
141
142 // If we're doing parallel GC, use this gang of threads.
143 FlexibleWorkGang* _workers;
144
145 // Full initialization is done in a concrete subtype's "initialize"
146 // function.
147 SharedHeap(CollectorPolicy* policy_);
148
149 // Returns true if the calling thread holds the heap lock,
150 // or the calling thread is a par gc thread and the heap_lock is held
151 // by the vm thread doing a gc operation.
152 bool heap_lock_held_for_gc();
153 // True if the heap_lock is held by the a non-gc thread invoking a gc
154 // operation.
155 bool _thread_holds_heap_lock_for_gc;
156
157 public:
158 static SharedHeap* heap() { return _sh; }
159
160 void set_barrier_set(BarrierSet* bs);
161 SubTasksDone* process_strong_tasks() { return _process_strong_tasks; }
162
163 // Does operations required after initialization has been done.
164 virtual void post_initialize();
165
166 // Initialization of ("weak") reference processing support
167 virtual void ref_processing_init();
168
169 // Iteration functions.
170 void oop_iterate(ExtendedOopClosure* cl) = 0;
171
172 // Iterate over all spaces in use in the heap, in an undefined order.
173 virtual void space_iterate(SpaceClosure* cl) = 0;
174
175 // A SharedHeap will contain some number of spaces. This finds the
176 // space whose reserved area contains the given address, or else returns
177 // NULL.
178 virtual Space* space_containing(const void* addr) const = 0;
179
180 bool no_gc_in_progress() { return !is_gc_active(); }
181
182 // Some collectors will perform "process_strong_roots" in parallel.
183 // Such a call will involve claiming some fine-grained tasks, such as
184 // scanning of threads. To make this process simpler, we provide the
185 // "strong_roots_parity()" method. Collectors that start parallel tasks
186 // whose threads invoke "process_strong_roots" must
187 // call "change_strong_roots_parity" in sequential code starting such a
188 // task. (This also means that a parallel thread may only call
189 // process_strong_roots once.)
190 //
191 // For calls to process_roots by sequential code, the parity is
192 // updated automatically.
193 //
194 // The idea is that objects representing fine-grained tasks, such as
195 // threads, will contain a "parity" field. A task will is claimed in the
196 // current "process_roots" call only if its parity field is the
197 // same as the "strong_roots_parity"; task claiming is accomplished by
198 // updating the parity field to the strong_roots_parity with a CAS.
199 //
200 // If the client meats this spec, then strong_roots_parity() will have
201 // the following properties:
202 // a) to return a different value than was returned before the last
203 // call to change_strong_roots_parity, and
204 // c) to never return a distinguished value (zero) with which such
205 // task-claiming variables may be initialized, to indicate "never
206 // claimed".
207 public:
208 int strong_roots_parity() { return _strong_roots_parity; }
209
210 // Call these in sequential code around process_roots.
211 // strong_roots_prologue calls change_strong_roots_parity, if
212 // parallel tasks are enabled.
213 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
214 // Used to implement the Thread work barrier.
215 static Monitor* _lock;
216
217 SharedHeap* _sh;
218 volatile jint _n_workers_done_with_threads;
219
220 public:
221 StrongRootsScope(SharedHeap* heap, bool activate = true);
222 ~StrongRootsScope();
223
224 // Mark that this thread is done with the Threads work.
225 void mark_worker_done_with_threads(uint n_workers);
226 // Wait until all n_workers are done with the Threads work.
227 void wait_until_all_workers_done_with_threads(uint n_workers);
228 };
229 friend class StrongRootsScope;
230
231 // The current active StrongRootScope
232 StrongRootsScope* _strong_roots_scope;
233
234 StrongRootsScope* active_strong_roots_scope() const;
235
236 private:
237 void register_strong_roots_scope(StrongRootsScope* scope);
238 void unregister_strong_roots_scope(StrongRootsScope* scope);
239 void change_strong_roots_parity();
240
241 public:
242 enum ScanningOption {
243 SO_None = 0x0,
244 SO_AllCodeCache = 0x8,
245 SO_ScavengeCodeCache = 0x10
246 };
247
248 FlexibleWorkGang* workers() const { return _workers; }
249
250 // Invoke the "do_oop" method the closure "roots" on all root locations.
251 // The "so" argument determines which roots the closure is applied to:
252 // "SO_None" does none;
253 // "SO_AllCodeCache" applies the closure to all elements of the CodeCache.
254 // "SO_ScavengeCodeCache" applies the closure to elements on the scavenge root list in the CodeCache.
255 void process_roots(bool activate_scope,
256 ScanningOption so,
257 OopClosure* strong_roots,
258 OopClosure* weak_roots,
259 CLDClosure* strong_cld_closure,
260 CLDClosure* weak_cld_closure,
261 CodeBlobClosure* code_roots,
262 PhaseTimeData* phase_durations = NULL);
263 void process_all_roots(bool activate_scope,
264 ScanningOption so,
265 OopClosure* roots,
266 CLDClosure* cld_closure,
267 CodeBlobClosure* code_roots,
268 PhaseTimeData* phase_durations = NULL);
269 void process_strong_roots(bool activate_scope,
270 ScanningOption so,
271 OopClosure* roots,
272 CLDClosure* cld_closure,
273 CodeBlobClosure* code_roots,
274 PhaseTimeData* phase_durations = NULL);
275
276
277 // Apply "root_closure" to the JNI weak roots..
278 void process_weak_roots(OopClosure* root_closure);
279
280 // The functions below are helper functions that a subclass of
281 // "SharedHeap" can use in the implementation of its virtual
282 // functions.
283
284 public:
285
286 // Do anything common to GC's.
287 virtual void gc_prologue(bool full) = 0;
288 virtual void gc_epilogue(bool full) = 0;
289
290 // Sets the number of parallel threads that will be doing tasks
291 // (such as process roots) subsequently.
292 virtual void set_par_threads(uint t);
293
294 int n_termination();
295 void set_n_termination(int t);
296
297 //
298 // New methods from CollectedHeap
299 //
300
301 // Some utilities.
302 void print_size_transition(outputStream* out,
303 size_t bytes_before,
304 size_t bytes_after,
305 size_t capacity);
306 };
307
308 inline SharedHeap::ScanningOption operator|(SharedHeap::ScanningOption so0, SharedHeap::ScanningOption so1) {
309 return static_cast<SharedHeap::ScanningOption>(static_cast<int>(so0) | static_cast<int>(so1));
310 }
311
312 #endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP