1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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7 * published by the Free Software Foundation.
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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).
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24
25 // A "SharedHeap" is an implementation of a java heap for HotSpot. This
26 // is an abstract class: there may be many different kinds of heaps. This
27 // class defines the functions that a heap must implement, and contains
28 // infrastructure common to all heaps.
29
30 class PermGen;
31 class Generation;
32 class BarrierSet;
33 class GenRemSet;
34 class Space;
35 class SpaceClosure;
36 class OopClosure;
37 class OopsInGenClosure;
38 class ObjectClosure;
39 class SubTasksDone;
40 class WorkGang;
41 class FlexibleWorkGang;
42 class CollectorPolicy;
43 class KlassHandle;
44
45 class SharedHeap : public CollectedHeap {
46 friend class VMStructs;
47
48 friend class VM_GC_Operation;
49 friend class VM_CGC_Operation;
50
51 private:
52 // For claiming strong_roots tasks.
53 SubTasksDone* _process_strong_tasks;
54
55 protected:
56 // There should be only a single instance of "SharedHeap" in a program.
57 // This is enforced with the protected constructor below, which will also
58 // set the static pointer "_sh" to that instance.
59 static SharedHeap* _sh;
60
61 // All heaps contain a "permanent generation." This is some ways
62 // similar to a generation in a generational system, in other ways not.
63 // See the "PermGen" class.
64 PermGen* _perm_gen;
65
66 // and the Gen Remembered Set, at least one good enough to scan the perm
67 // gen.
68 GenRemSet* _rem_set;
69
70 // A gc policy, controls global gc resource issues
71 CollectorPolicy *_collector_policy;
72
73 // See the discussion below, in the specification of the reader function
74 // for this variable.
75 int _strong_roots_parity;
76
77 // If we're doing parallel GC, use this gang of threads.
78 FlexibleWorkGang* _workers;
79
80 // Number of parallel threads currently working on GC tasks.
81 // O indicates use sequential code; 1 means use parallel code even with
82 // only one thread, for performance testing purposes.
83 int _n_par_threads;
84
85 // Full initialization is done in a concrete subtype's "initialize"
86 // function.
87 SharedHeap(CollectorPolicy* policy_);
88
89 // Returns true if the calling thread holds the heap lock,
90 // or the calling thread is a par gc thread and the heap_lock is held
91 // by the vm thread doing a gc operation.
92 bool heap_lock_held_for_gc();
93 // True if the heap_lock is held by the a non-gc thread invoking a gc
94 // operation.
95 bool _thread_holds_heap_lock_for_gc;
96
97 public:
98 static SharedHeap* heap() { return _sh; }
99
100 CollectorPolicy *collector_policy() const { return _collector_policy; }
101
102 void set_barrier_set(BarrierSet* bs);
103
104 // Does operations required after initialization has been done.
105 virtual void post_initialize();
106
107 // Initialization of ("weak") reference processing support
108 virtual void ref_processing_init();
109
110 void set_perm(PermGen* perm_gen) { _perm_gen = perm_gen; }
111
112 // This function returns the "GenRemSet" object that allows us to scan
113 // generations; at least the perm gen, possibly more in a fully
114 // generational heap.
115 GenRemSet* rem_set() { return _rem_set; }
116
117 // These function return the "permanent" generation, in which
118 // reflective objects are allocated and stored. Two versions, the second
119 // of which returns the view of the perm gen as a generation.
120 PermGen* perm() const { return _perm_gen; }
121 Generation* perm_gen() const { return _perm_gen->as_gen(); }
122
123 // Iteration functions.
124 void oop_iterate(OopClosure* cl) = 0;
125
126 // Same as above, restricted to a memory region.
127 virtual void oop_iterate(MemRegion mr, OopClosure* cl) = 0;
128
129 // Iterate over all objects allocated since the last collection, calling
130 // "cl->do_object" on each. The heap must have been initialized properly
131 // to support this function, or else this call will fail.
132 virtual void object_iterate_since_last_GC(ObjectClosure* cl) = 0;
133
134 // Iterate over all spaces in use in the heap, in an undefined order.
135 virtual void space_iterate(SpaceClosure* cl) = 0;
136
137 // A SharedHeap will contain some number of spaces. This finds the
138 // space whose reserved area contains the given address, or else returns
139 // NULL.
140 virtual Space* space_containing(const void* addr) const = 0;
141
142 bool no_gc_in_progress() { return !is_gc_active(); }
143
144 // Some collectors will perform "process_strong_roots" in parallel.
145 // Such a call will involve claiming some fine-grained tasks, such as
146 // scanning of threads. To make this process simpler, we provide the
147 // "strong_roots_parity()" method. Collectors that start parallel tasks
148 // whose threads invoke "process_strong_roots" must
149 // call "change_strong_roots_parity" in sequential code starting such a
150 // task. (This also means that a parallel thread may only call
151 // process_strong_roots once.)
152 //
153 // For calls to process_strong_roots by sequential code, the parity is
154 // updated automatically.
155 //
156 // The idea is that objects representing fine-grained tasks, such as
157 // threads, will contain a "parity" field. A task will is claimed in the
158 // current "process_strong_roots" call only if its parity field is the
159 // same as the "strong_roots_parity"; task claiming is accomplished by
160 // updating the parity field to the strong_roots_parity with a CAS.
161 //
162 // If the client meats this spec, then strong_roots_parity() will have
163 // the following properties:
164 // a) to return a different value than was returned before the last
165 // call to change_strong_roots_parity, and
166 // c) to never return a distinguished value (zero) with which such
167 // task-claiming variables may be initialized, to indicate "never
168 // claimed".
169 private:
170 void change_strong_roots_parity();
171 public:
172 int strong_roots_parity() { return _strong_roots_parity; }
173
174 // Call these in sequential code around process_strong_roots.
175 // strong_roots_prologue calls change_strong_roots_parity, if
176 // parallel tasks are enabled.
177 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
178 public:
179 StrongRootsScope(SharedHeap* outer, bool activate = true);
180 ~StrongRootsScope();
181 };
182 friend class StrongRootsScope;
183
184 enum ScanningOption {
185 SO_None = 0x0,
186 SO_AllClasses = 0x1,
187 SO_SystemClasses = 0x2,
188 SO_Symbols = 0x4,
189 SO_Strings = 0x8,
190 SO_CodeCache = 0x10
191 };
192
193 FlexibleWorkGang* workers() const { return _workers; }
194
195 // Sets the number of parallel threads that will be doing tasks
196 // (such as process strong roots) subsequently.
197 virtual void set_par_threads(int t);
198
199 // Number of threads currently working on GC tasks.
200 int n_par_threads() { return _n_par_threads; }
201
202 // Invoke the "do_oop" method the closure "roots" on all root locations.
203 // If "collecting_perm_gen" is false, then roots that may only contain
204 // references to permGen objects are not scanned. If true, the
205 // "perm_gen" closure is applied to all older-to-younger refs in the
206 // permanent generation. The "so" argument determines which of roots
207 // the closure is applied to:
208 // "SO_None" does none;
209 // "SO_AllClasses" applies the closure to all entries in the SystemDictionary;
210 // "SO_SystemClasses" to all the "system" classes and loaders;
211 // "SO_Symbols" applies the closure to all entries in SymbolsTable;
212 // "SO_Strings" applies the closure to all entries in StringTable;
213 // "SO_CodeCache" applies the closure to all elements of the CodeCache.
214 void process_strong_roots(bool activate_scope,
215 bool collecting_perm_gen,
216 ScanningOption so,
217 OopClosure* roots,
218 CodeBlobClosure* code_roots,
219 OopsInGenClosure* perm_blk);
220
221 // Apply "blk" to all the weak roots of the system. These include
222 // JNI weak roots, the code cache, system dictionary, symbol table,
223 // string table.
224 void process_weak_roots(OopClosure* root_closure,
225 CodeBlobClosure* code_roots,
226 OopClosure* non_root_closure);
227
228 // The functions below are helper functions that a subclass of
229 // "SharedHeap" can use in the implementation of its virtual
230 // functions.
231
232 public:
233
234 // Do anything common to GC's.
235 virtual void gc_prologue(bool full) = 0;
236 virtual void gc_epilogue(bool full) = 0;
237
238 //
239 // New methods from CollectedHeap
240 //
241
242 size_t permanent_capacity() const {
243 assert(perm_gen(), "NULL perm gen");
244 return perm_gen()->capacity();
245 }
246
247 size_t permanent_used() const {
248 assert(perm_gen(), "NULL perm gen");
249 return perm_gen()->used();
250 }
251
252 bool is_in_permanent(const void *p) const {
253 assert(perm_gen(), "NULL perm gen");
254 return perm_gen()->is_in_reserved(p);
255 }
256
257 // Different from is_in_permanent in that is_in_permanent
258 // only checks if p is in the reserved area of the heap
259 // and this checks to see if it in the commited area.
260 // This is typically used by things like the forte stackwalker
261 // during verification of suspicious frame values.
262 bool is_permanent(const void *p) const {
263 assert(perm_gen(), "NULL perm gen");
264 return perm_gen()->is_in(p);
265 }
266
267 HeapWord* permanent_mem_allocate(size_t size) {
268 assert(perm_gen(), "NULL perm gen");
269 return _perm_gen->mem_allocate(size);
270 }
271
272 void permanent_oop_iterate(OopClosure* cl) {
273 assert(perm_gen(), "NULL perm gen");
274 _perm_gen->oop_iterate(cl);
275 }
276
277 void permanent_object_iterate(ObjectClosure* cl) {
278 assert(perm_gen(), "NULL perm gen");
279 _perm_gen->object_iterate(cl);
280 }
281
282 // Some utilities.
283 void print_size_transition(outputStream* out,
284 size_t bytes_before,
285 size_t bytes_after,
286 size_t capacity);
287 };