1 /*
2 * Copyright (c) 2000, 2009, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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).
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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 CollectorPolicy;
42 class KlassHandle;
43
44 class SharedHeap : public CollectedHeap {
45 friend class VMStructs;
46
47 friend class VM_GC_Operation;
48 friend class VM_CGC_Operation;
49
50 private:
51 // For claiming strong_roots tasks.
52 SubTasksDone* _process_strong_tasks;
53
54 protected:
55 // There should be only a single instance of "SharedHeap" in a program.
56 // This is enforced with the protected constructor below, which will also
57 // set the static pointer "_sh" to that instance.
58 static SharedHeap* _sh;
59
60 // All heaps contain a "permanent generation." This is some ways
61 // similar to a generation in a generational system, in other ways not.
62 // See the "PermGen" class.
63 PermGen* _perm_gen;
64
65 // and the Gen Remembered Set, at least one good enough to scan the perm
66 // gen.
67 GenRemSet* _rem_set;
68
69 // A gc policy, controls global gc resource issues
70 CollectorPolicy *_collector_policy;
71
72 // See the discussion below, in the specification of the reader function
73 // for this variable.
74 int _strong_roots_parity;
75
76 // If we're doing parallel GC, use this gang of threads.
77 WorkGang* _workers;
78
79 // Number of parallel threads currently working on GC tasks.
80 // O indicates use sequential code; 1 means use parallel code even with
81 // only one thread, for performance testing purposes.
82 int _n_par_threads;
83
84 // Full initialization is done in a concrete subtype's "initialize"
85 // function.
86 SharedHeap(CollectorPolicy* policy_);
87
88 // Returns true if the calling thread holds the heap lock,
89 // or the calling thread is a par gc thread and the heap_lock is held
90 // by the vm thread doing a gc operation.
91 bool heap_lock_held_for_gc();
92 // True if the heap_lock is held by the a non-gc thread invoking a gc
93 // operation.
94 bool _thread_holds_heap_lock_for_gc;
95
96 public:
97 static SharedHeap* heap() { return _sh; }
98
99 CollectorPolicy *collector_policy() const { return _collector_policy; }
100
101 void set_barrier_set(BarrierSet* bs);
102
103 // Does operations required after initialization has been done.
104 virtual void post_initialize();
105
106 // Initialization of ("weak") reference processing support
107 virtual void ref_processing_init();
108
109 void set_perm(PermGen* perm_gen) { _perm_gen = perm_gen; }
110
111 // This function returns the "GenRemSet" object that allows us to scan
112 // generations; at least the perm gen, possibly more in a fully
113 // generational heap.
114 GenRemSet* rem_set() { return _rem_set; }
115
116 // These function return the "permanent" generation, in which
117 // reflective objects are allocated and stored. Two versions, the second
118 // of which returns the view of the perm gen as a generation.
119 PermGen* perm() const { return _perm_gen; }
120 Generation* perm_gen() const { return _perm_gen->as_gen(); }
121
122 // Iteration functions.
123 void oop_iterate(OopClosure* cl) = 0;
124
125 // Same as above, restricted to a memory region.
126 virtual void oop_iterate(MemRegion mr, OopClosure* cl) = 0;
127
128 // Iterate over all objects allocated since the last collection, calling
129 // "cl->do_object" on each. The heap must have been initialized properly
130 // to support this function, or else this call will fail.
131 virtual void object_iterate_since_last_GC(ObjectClosure* cl) = 0;
132
133 // Iterate over all spaces in use in the heap, in an undefined order.
134 virtual void space_iterate(SpaceClosure* cl) = 0;
135
136 // A SharedHeap will contain some number of spaces. This finds the
137 // space whose reserved area contains the given address, or else returns
138 // NULL.
139 virtual Space* space_containing(const void* addr) const = 0;
140
141 bool no_gc_in_progress() { return !is_gc_active(); }
142
143 // Some collectors will perform "process_strong_roots" in parallel.
144 // Such a call will involve claiming some fine-grained tasks, such as
145 // scanning of threads. To make this process simpler, we provide the
146 // "strong_roots_parity()" method. Collectors that start parallel tasks
147 // whose threads invoke "process_strong_roots" must
148 // call "change_strong_roots_parity" in sequential code starting such a
149 // task. (This also means that a parallel thread may only call
150 // process_strong_roots once.)
151 //
152 // For calls to process_strong_roots by sequential code, the parity is
153 // updated automatically.
154 //
155 // The idea is that objects representing fine-grained tasks, such as
156 // threads, will contain a "parity" field. A task will is claimed in the
157 // current "process_strong_roots" call only if its parity field is the
158 // same as the "strong_roots_parity"; task claiming is accomplished by
159 // updating the parity field to the strong_roots_parity with a CAS.
160 //
161 // If the client meats this spec, then strong_roots_parity() will have
162 // the following properties:
163 // a) to return a different value than was returned before the last
164 // call to change_strong_roots_parity, and
165 // c) to never return a distinguished value (zero) with which such
166 // task-claiming variables may be initialized, to indicate "never
167 // claimed".
168 private:
169 void change_strong_roots_parity();
170 public:
171 int strong_roots_parity() { return _strong_roots_parity; }
172
173 // Call these in sequential code around process_strong_roots.
174 // strong_roots_prologue calls change_strong_roots_parity, if
175 // parallel tasks are enabled.
176 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
177 public:
178 StrongRootsScope(SharedHeap* outer, bool activate = true);
179 ~StrongRootsScope();
180 };
181 friend class StrongRootsScope;
182
183 enum ScanningOption {
184 SO_None = 0x0,
185 SO_AllClasses = 0x1,
186 SO_SystemClasses = 0x2,
187 SO_Symbols = 0x4,
188 SO_Strings = 0x8,
189 SO_CodeCache = 0x10
190 };
191
192 WorkGang* workers() const { return _workers; }
193
194 // Sets the number of parallel threads that will be doing tasks
195 // (such as process strong roots) subsequently.
196 virtual void set_par_threads(int t);
197
198 // Number of threads currently working on GC tasks.
199 int n_par_threads() { return _n_par_threads; }
200
201 // Invoke the "do_oop" method the closure "roots" on all root locations.
202 // If "collecting_perm_gen" is false, then roots that may only contain
203 // references to permGen objects are not scanned. If true, the
204 // "perm_gen" closure is applied to all older-to-younger refs in the
205 // permanent generation. The "so" argument determines which of roots
206 // the closure is applied to:
207 // "SO_None" does none;
208 // "SO_AllClasses" applies the closure to all entries in the SystemDictionary;
209 // "SO_SystemClasses" to all the "system" classes and loaders;
210 // "SO_Symbols" applies the closure to all entries in SymbolsTable;
211 // "SO_Strings" applies the closure to all entries in StringTable;
212 // "SO_CodeCache" applies the closure to all elements of the CodeCache.
213 void process_strong_roots(bool activate_scope,
214 bool collecting_perm_gen,
215 ScanningOption so,
216 OopClosure* roots,
217 CodeBlobClosure* code_roots,
218 OopsInGenClosure* perm_blk);
219
220 // Apply "blk" to all the weak roots of the system. These include
221 // JNI weak roots, the code cache, system dictionary, symbol table,
222 // string table.
223 void process_weak_roots(OopClosure* root_closure,
224 CodeBlobClosure* code_roots,
225 OopClosure* non_root_closure);
226
227 // The functions below are helper functions that a subclass of
228 // "SharedHeap" can use in the implementation of its virtual
229 // functions.
230
231 public:
232
233 // Do anything common to GC's.
234 virtual void gc_prologue(bool full) = 0;
235 virtual void gc_epilogue(bool full) = 0;
236
237 //
238 // New methods from CollectedHeap
239 //
240
241 size_t permanent_capacity() const {
242 assert(perm_gen(), "NULL perm gen");
243 return perm_gen()->capacity();
244 }
245
246 size_t permanent_used() const {
247 assert(perm_gen(), "NULL perm gen");
248 return perm_gen()->used();
249 }
250
251 bool is_in_permanent(const void *p) const {
252 assert(perm_gen(), "NULL perm gen");
253 return perm_gen()->is_in_reserved(p);
254 }
255
256 // Different from is_in_permanent in that is_in_permanent
257 // only checks if p is in the reserved area of the heap
258 // and this checks to see if it in the commited area.
259 // This is typically used by things like the forte stackwalker
260 // during verification of suspicious frame values.
261 bool is_permanent(const void *p) const {
262 assert(perm_gen(), "NULL perm gen");
263 return perm_gen()->is_in(p);
264 }
265
266 HeapWord* permanent_mem_allocate(size_t size) {
267 assert(perm_gen(), "NULL perm gen");
268 return _perm_gen->mem_allocate(size);
269 }
270
271 void permanent_oop_iterate(OopClosure* cl) {
272 assert(perm_gen(), "NULL perm gen");
273 _perm_gen->oop_iterate(cl);
274 }
275
276 void permanent_object_iterate(ObjectClosure* cl) {
277 assert(perm_gen(), "NULL perm gen");
278 _perm_gen->object_iterate(cl);
279 }
280
281 // Some utilities.
282 void print_size_transition(outputStream* out,
283 size_t bytes_before,
284 size_t bytes_after,
285 size_t capacity);
286 };