Mon, 21 Nov 2011 07:47:34 +0100
7110718: -XX:MarkSweepAlwaysCompactCount=0 crashes the JVM
Summary: Interpret MarkSweepAlwaysCompactCount < 1 as never do full compaction
Reviewed-by: ysr, tonyp, jmasa, johnc
1 /*
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25 #ifndef SHARE_VM_MEMORY_SHAREDHEAP_HPP
26 #define SHARE_VM_MEMORY_SHAREDHEAP_HPP
28 #include "gc_interface/collectedHeap.hpp"
29 #include "memory/generation.hpp"
30 #include "memory/permGen.hpp"
32 // A "SharedHeap" is an implementation of a java heap for HotSpot. This
33 // is an abstract class: there may be many different kinds of heaps. This
34 // class defines the functions that a heap must implement, and contains
35 // infrastructure common to all heaps.
37 class PermGen;
38 class Generation;
39 class BarrierSet;
40 class GenRemSet;
41 class Space;
42 class SpaceClosure;
43 class OopClosure;
44 class OopsInGenClosure;
45 class ObjectClosure;
46 class SubTasksDone;
47 class WorkGang;
48 class FlexibleWorkGang;
49 class CollectorPolicy;
50 class KlassHandle;
52 class SharedHeap : public CollectedHeap {
53 friend class VMStructs;
55 friend class VM_GC_Operation;
56 friend class VM_CGC_Operation;
58 private:
59 // For claiming strong_roots tasks.
60 SubTasksDone* _process_strong_tasks;
62 protected:
63 // There should be only a single instance of "SharedHeap" in a program.
64 // This is enforced with the protected constructor below, which will also
65 // set the static pointer "_sh" to that instance.
66 static SharedHeap* _sh;
68 // All heaps contain a "permanent generation." This is some ways
69 // similar to a generation in a generational system, in other ways not.
70 // See the "PermGen" class.
71 PermGen* _perm_gen;
73 // and the Gen Remembered Set, at least one good enough to scan the perm
74 // gen.
75 GenRemSet* _rem_set;
77 // A gc policy, controls global gc resource issues
78 CollectorPolicy *_collector_policy;
80 // See the discussion below, in the specification of the reader function
81 // for this variable.
82 int _strong_roots_parity;
84 // If we're doing parallel GC, use this gang of threads.
85 FlexibleWorkGang* _workers;
87 // Number of parallel threads currently working on GC tasks.
88 // O indicates use sequential code; 1 means use parallel code even with
89 // only one thread, for performance testing purposes.
90 int _n_par_threads;
92 // Full initialization is done in a concrete subtype's "initialize"
93 // function.
94 SharedHeap(CollectorPolicy* policy_);
96 // Returns true if the calling thread holds the heap lock,
97 // or the calling thread is a par gc thread and the heap_lock is held
98 // by the vm thread doing a gc operation.
99 bool heap_lock_held_for_gc();
100 // True if the heap_lock is held by the a non-gc thread invoking a gc
101 // operation.
102 bool _thread_holds_heap_lock_for_gc;
104 public:
105 static SharedHeap* heap() { return _sh; }
107 CollectorPolicy *collector_policy() const { return _collector_policy; }
109 void set_barrier_set(BarrierSet* bs);
111 // Does operations required after initialization has been done.
112 virtual void post_initialize();
114 // Initialization of ("weak") reference processing support
115 virtual void ref_processing_init();
117 void set_perm(PermGen* perm_gen) { _perm_gen = perm_gen; }
119 // This function returns the "GenRemSet" object that allows us to scan
120 // generations; at least the perm gen, possibly more in a fully
121 // generational heap.
122 GenRemSet* rem_set() { return _rem_set; }
124 // These function return the "permanent" generation, in which
125 // reflective objects are allocated and stored. Two versions, the second
126 // of which returns the view of the perm gen as a generation.
127 PermGen* perm() const { return _perm_gen; }
128 Generation* perm_gen() const { return _perm_gen->as_gen(); }
130 // Iteration functions.
131 void oop_iterate(OopClosure* cl) = 0;
133 // Same as above, restricted to a memory region.
134 virtual void oop_iterate(MemRegion mr, OopClosure* cl) = 0;
136 // Iterate over all objects allocated since the last collection, calling
137 // "cl->do_object" on each. The heap must have been initialized properly
138 // to support this function, or else this call will fail.
139 virtual void object_iterate_since_last_GC(ObjectClosure* cl) = 0;
141 // Iterate over all spaces in use in the heap, in an undefined order.
142 virtual void space_iterate(SpaceClosure* cl) = 0;
144 // A SharedHeap will contain some number of spaces. This finds the
145 // space whose reserved area contains the given address, or else returns
146 // NULL.
147 virtual Space* space_containing(const void* addr) const = 0;
149 bool no_gc_in_progress() { return !is_gc_active(); }
151 // Some collectors will perform "process_strong_roots" in parallel.
152 // Such a call will involve claiming some fine-grained tasks, such as
153 // scanning of threads. To make this process simpler, we provide the
154 // "strong_roots_parity()" method. Collectors that start parallel tasks
155 // whose threads invoke "process_strong_roots" must
156 // call "change_strong_roots_parity" in sequential code starting such a
157 // task. (This also means that a parallel thread may only call
158 // process_strong_roots once.)
159 //
160 // For calls to process_strong_roots by sequential code, the parity is
161 // updated automatically.
162 //
163 // The idea is that objects representing fine-grained tasks, such as
164 // threads, will contain a "parity" field. A task will is claimed in the
165 // current "process_strong_roots" call only if its parity field is the
166 // same as the "strong_roots_parity"; task claiming is accomplished by
167 // updating the parity field to the strong_roots_parity with a CAS.
168 //
169 // If the client meats this spec, then strong_roots_parity() will have
170 // the following properties:
171 // a) to return a different value than was returned before the last
172 // call to change_strong_roots_parity, and
173 // c) to never return a distinguished value (zero) with which such
174 // task-claiming variables may be initialized, to indicate "never
175 // claimed".
176 private:
177 void change_strong_roots_parity();
178 public:
179 int strong_roots_parity() { return _strong_roots_parity; }
181 // Call these in sequential code around process_strong_roots.
182 // strong_roots_prologue calls change_strong_roots_parity, if
183 // parallel tasks are enabled.
184 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
185 public:
186 StrongRootsScope(SharedHeap* outer, bool activate = true);
187 ~StrongRootsScope();
188 };
189 friend class StrongRootsScope;
191 enum ScanningOption {
192 SO_None = 0x0,
193 SO_AllClasses = 0x1,
194 SO_SystemClasses = 0x2,
195 SO_Strings = 0x4,
196 SO_CodeCache = 0x8
197 };
199 FlexibleWorkGang* workers() const { return _workers; }
201 // Sets the number of parallel threads that will be doing tasks
202 // (such as process strong roots) subsequently.
203 virtual void set_par_threads(int t);
205 // Number of threads currently working on GC tasks.
206 int n_par_threads() { return _n_par_threads; }
208 // Invoke the "do_oop" method the closure "roots" on all root locations.
209 // If "collecting_perm_gen" is false, then roots that may only contain
210 // references to permGen objects are not scanned; instead, in that case,
211 // the "perm_blk" closure is applied to all outgoing refs in the
212 // permanent generation. The "so" argument determines which of roots
213 // the closure is applied to:
214 // "SO_None" does none;
215 // "SO_AllClasses" applies the closure to all entries in the SystemDictionary;
216 // "SO_SystemClasses" to all the "system" classes and loaders;
217 // "SO_Strings" applies the closure to all entries in StringTable;
218 // "SO_CodeCache" applies the closure to all elements of the CodeCache.
219 void process_strong_roots(bool activate_scope,
220 bool collecting_perm_gen,
221 ScanningOption so,
222 OopClosure* roots,
223 CodeBlobClosure* code_roots,
224 OopsInGenClosure* perm_blk);
226 // Apply "blk" to all the weak roots of the system. These include
227 // JNI weak roots, the code cache, system dictionary, symbol table,
228 // string table.
229 void process_weak_roots(OopClosure* root_closure,
230 CodeBlobClosure* code_roots,
231 OopClosure* non_root_closure);
233 // The functions below are helper functions that a subclass of
234 // "SharedHeap" can use in the implementation of its virtual
235 // functions.
237 public:
239 // Do anything common to GC's.
240 virtual void gc_prologue(bool full) = 0;
241 virtual void gc_epilogue(bool full) = 0;
243 //
244 // New methods from CollectedHeap
245 //
247 size_t permanent_capacity() const {
248 assert(perm_gen(), "NULL perm gen");
249 return perm_gen()->capacity();
250 }
252 size_t permanent_used() const {
253 assert(perm_gen(), "NULL perm gen");
254 return perm_gen()->used();
255 }
257 bool is_in_permanent(const void *p) const {
258 assert(perm_gen(), "NULL perm gen");
259 return perm_gen()->is_in_reserved(p);
260 }
262 // Different from is_in_permanent in that is_in_permanent
263 // only checks if p is in the reserved area of the heap
264 // and this checks to see if it in the commited area.
265 // This is typically used by things like the forte stackwalker
266 // during verification of suspicious frame values.
267 bool is_permanent(const void *p) const {
268 assert(perm_gen(), "NULL perm gen");
269 return perm_gen()->is_in(p);
270 }
272 HeapWord* permanent_mem_allocate(size_t size) {
273 assert(perm_gen(), "NULL perm gen");
274 return _perm_gen->mem_allocate(size);
275 }
277 void permanent_oop_iterate(OopClosure* cl) {
278 assert(perm_gen(), "NULL perm gen");
279 _perm_gen->oop_iterate(cl);
280 }
282 void permanent_object_iterate(ObjectClosure* cl) {
283 assert(perm_gen(), "NULL perm gen");
284 _perm_gen->object_iterate(cl);
285 }
287 // Some utilities.
288 void print_size_transition(outputStream* out,
289 size_t bytes_before,
290 size_t bytes_after,
291 size_t capacity);
292 };
294 #endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP