1 /* 2 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 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). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 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; 106 107 private: 108 // For claiming strong_roots tasks. 109 SubTasksDone* _process_strong_tasks; 110 111 protected: 112 // There should be only a single instance of "SharedHeap" in a program. 113 // This is enforced with the protected constructor below, which will also 114 // set the static pointer "_sh" to that instance. 115 static SharedHeap* _sh; 116 117 // A gc policy, controls global gc resource issues 118 CollectorPolicy *_collector_policy; 119 120 // See the discussion below, in the specification of the reader function 121 // for this variable. 122 int _strong_roots_parity; 123 124 // If we're doing parallel GC, use this gang of threads. 125 FlexibleWorkGang* _workers; 126 127 // Full initialization is done in a concrete subtype's "initialize" 128 // function. 129 SharedHeap(CollectorPolicy* policy_); 130 131 // Returns true if the calling thread holds the heap lock, 132 // or the calling thread is a par gc thread and the heap_lock is held 133 // by the vm thread doing a gc operation. 134 bool heap_lock_held_for_gc(); 135 // True if the heap_lock is held by the a non-gc thread invoking a gc 136 // operation. 137 bool _thread_holds_heap_lock_for_gc; 138 139 public: 140 static SharedHeap* heap() { return _sh; } 141 142 void set_barrier_set(BarrierSet* bs); 143 SubTasksDone* process_strong_tasks() { return _process_strong_tasks; } 144 145 // Does operations required after initialization has been done. 146 virtual void post_initialize(); 147 148 // Initialization of ("weak") reference processing support 149 virtual void ref_processing_init(); 150 151 // Iteration functions. 152 void oop_iterate(ExtendedOopClosure* cl) = 0; 153 154 // Iterate over all spaces in use in the heap, in an undefined order. 155 virtual void space_iterate(SpaceClosure* cl) = 0; 156 157 // A SharedHeap will contain some number of spaces. This finds the 158 // space whose reserved area contains the given address, or else returns 159 // NULL. 160 virtual Space* space_containing(const void* addr) const = 0; 161 162 bool no_gc_in_progress() { return !is_gc_active(); } 163 164 // Some collectors will perform "process_strong_roots" in parallel. 165 // Such a call will involve claiming some fine-grained tasks, such as 166 // scanning of threads. To make this process simpler, we provide the 167 // "strong_roots_parity()" method. Collectors that start parallel tasks 168 // whose threads invoke "process_strong_roots" must 169 // call "change_strong_roots_parity" in sequential code starting such a 170 // task. (This also means that a parallel thread may only call 171 // process_strong_roots once.) 172 // 173 // For calls to process_roots by sequential code, the parity is 174 // updated automatically. 175 // 176 // The idea is that objects representing fine-grained tasks, such as 177 // threads, will contain a "parity" field. A task will is claimed in the 178 // current "process_roots" call only if its parity field is the 179 // same as the "strong_roots_parity"; task claiming is accomplished by 180 // updating the parity field to the strong_roots_parity with a CAS. 181 // 182 // If the client meats this spec, then strong_roots_parity() will have 183 // the following properties: 184 // a) to return a different value than was returned before the last 185 // call to change_strong_roots_parity, and 186 // c) to never return a distinguished value (zero) with which such 187 // task-claiming variables may be initialized, to indicate "never 188 // claimed". 189 public: 190 int strong_roots_parity() { return _strong_roots_parity; } 191 192 // Call these in sequential code around process_roots. 193 // strong_roots_prologue calls change_strong_roots_parity, if 194 // parallel tasks are enabled. 195 class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope { 196 // Used to implement the Thread work barrier. 197 static Monitor* _lock; 198 199 SharedHeap* _sh; 200 volatile jint _n_workers_done_with_threads; 201 202 public: 203 StrongRootsScope(SharedHeap* heap, bool activate = true); 204 ~StrongRootsScope(); 205 206 // Mark that this thread is done with the Threads work. 207 void mark_worker_done_with_threads(uint n_workers); 208 // Wait until all n_workers are done with the Threads work. 209 void wait_until_all_workers_done_with_threads(uint n_workers); 210 }; 211 friend class StrongRootsScope; 212 213 // The current active StrongRootScope 214 StrongRootsScope* _strong_roots_scope; 215 216 StrongRootsScope* active_strong_roots_scope() const; 217 218 private: 219 void register_strong_roots_scope(StrongRootsScope* scope); 220 void unregister_strong_roots_scope(StrongRootsScope* scope); 221 void change_strong_roots_parity(); 222 223 public: 224 enum ScanningOption { 225 SO_None = 0x0, 226 SO_AllCodeCache = 0x8, 227 SO_ScavengeCodeCache = 0x10 228 }; 229 230 FlexibleWorkGang* workers() const { return _workers; } 231 232 // Invoke the "do_oop" method the closure "roots" on all root locations. 233 // The "so" argument determines which roots the closure is applied to: 234 // "SO_None" does none; 235 // "SO_AllCodeCache" applies the closure to all elements of the CodeCache. 236 // "SO_ScavengeCodeCache" applies the closure to elements on the scavenge root list in the CodeCache. 237 void process_roots(bool activate_scope, 238 ScanningOption so, 239 OopClosure* strong_roots, 240 OopClosure* weak_roots, 241 CLDClosure* strong_cld_closure, 242 CLDClosure* weak_cld_closure, 243 CodeBlobClosure* code_roots); 244 void process_all_roots(bool activate_scope, 245 ScanningOption so, 246 OopClosure* roots, 247 CLDClosure* cld_closure, 248 CodeBlobClosure* code_roots); 249 void process_strong_roots(bool activate_scope, 250 ScanningOption so, 251 OopClosure* roots, 252 CLDClosure* cld_closure, 253 CodeBlobClosure* code_roots); 254 255 256 // Apply "root_closure" to the JNI weak roots.. 257 void process_weak_roots(OopClosure* root_closure); 258 259 // The functions below are helper functions that a subclass of 260 // "SharedHeap" can use in the implementation of its virtual 261 // functions. 262 263 public: 264 265 // Do anything common to GC's. 266 virtual void gc_prologue(bool full) = 0; 267 virtual void gc_epilogue(bool full) = 0; 268 269 // Sets the number of parallel threads that will be doing tasks 270 // (such as process roots) subsequently. 271 virtual void set_par_threads(uint t); 272 273 int n_termination(); 274 void set_n_termination(int t); 275 276 // 277 // New methods from CollectedHeap 278 // 279 280 // Some utilities. 281 void print_size_transition(outputStream* out, 282 size_t bytes_before, 283 size_t bytes_after, 284 size_t capacity); 285 }; 286 287 inline SharedHeap::ScanningOption operator|(SharedHeap::ScanningOption so0, SharedHeap::ScanningOption so1) { 288 return static_cast<SharedHeap::ScanningOption>(static_cast<int>(so0) | static_cast<int>(so1)); 289 } 290 291 #endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP