1 /* 2 * Copyright (c) 2018, 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_GC_SHARED_OOPSTORAGE_HPP 26 #define SHARE_GC_SHARED_OOPSTORAGE_HPP 27 28 #include "memory/allocation.hpp" 29 #include "oops/oop.hpp" 30 #include "utilities/globalDefinitions.hpp" 31 #include "utilities/macros.hpp" 32 33 class Mutex; 34 class outputStream; 35 36 // OopStorage supports management of off-heap references to objects allocated 37 // in the Java heap. An OopStorage object provides a set of Java object 38 // references (oop values), which clients refer to via oop* handles to the 39 // associated OopStorage entries. Clients allocate entries to create a 40 // (possibly weak) reference to a Java object, use that reference, and release 41 // the reference when no longer needed. 42 // 43 // The garbage collector must know about all OopStorage objects and their 44 // reference strength. OopStorage provides the garbage collector with support 45 // for iteration over all the allocated entries. 46 // 47 // There are several categories of interaction with an OopStorage object. 48 // 49 // (1) allocation and release of entries, by the mutator or the VM. 50 // (2) iteration by the garbage collector, possibly concurrent with mutator. 51 // (3) iteration by other, non-GC, tools (only at safepoints). 52 // (4) cleanup of unused internal storage, possibly concurrent with mutator. 53 // 54 // A goal of OopStorage is to make these interactions thread-safe, while 55 // minimizing potential lock contention issues within and between these 56 // categories. In particular, support for concurrent iteration by the garbage 57 // collector, under certain restrictions, is required. Further, it must not 58 // block nor be blocked by other operations for long periods. 59 // 60 // Internally, OopStorage is a set of Block objects, from which entries are 61 // allocated and released. A block contains an oop[] and a bitmask indicating 62 // which entries are in use (have been allocated and not yet released). New 63 // blocks are constructed and added to the storage object when an entry 64 // allocation request is made and there are no blocks with unused entries. 65 // Blocks may be removed and deleted when empty. 66 // 67 // There are two important (and somewhat intertwined) protocols governing 68 // concurrent access to a storage object. These are the Concurrent Iteration 69 // Protocol and the Allocation Protocol. See the ParState class for a 70 // discussion of concurrent iteration and the management of thread 71 // interactions for this protocol. Similarly, see the allocate() function for 72 // a discussion of allocation. 73 74 class OopStorage : public CHeapObj<mtGC> { 75 public: 76 OopStorage(const char* name, Mutex* allocation_mutex, Mutex* active_mutex); 77 ~OopStorage(); 78 79 // These count and usage accessors are racy unless at a safepoint. 80 81 // The number of allocated and not yet released entries. 82 size_t allocation_count() const; 83 84 // The number of blocks of entries. Useful for sizing parallel iteration. 85 size_t block_count() const; 86 87 // Total number of blocks * memory allocation per block, plus 88 // bookkeeping overhead, including this storage object. 89 size_t total_memory_usage() const; 90 91 enum EntryStatus { 92 INVALID_ENTRY, 93 UNALLOCATED_ENTRY, 94 ALLOCATED_ENTRY 95 }; 96 97 // Locks _allocation_mutex. 98 // precondition: ptr != NULL. 99 EntryStatus allocation_status(const oop* ptr) const; 100 101 // Allocates and returns a new entry. Returns NULL if memory allocation 102 // failed. Locks _allocation_mutex. 103 // postcondition: *result == NULL. 104 oop* allocate(); 105 106 // Deallocates ptr. No locking. 107 // precondition: ptr is a valid allocated entry. 108 // precondition: *ptr == NULL. 109 void release(const oop* ptr); 110 111 // Releases all the ptrs. Possibly faster than individual calls to 112 // release(oop*). Best if ptrs is sorted by address. No locking. 113 // precondition: All elements of ptrs are valid allocated entries. 114 // precondition: *ptrs[i] == NULL, for i in [0,size). 115 void release(const oop* const* ptrs, size_t size); 116 117 // Applies f to each allocated entry's location. f must be a function or 118 // function object. Assume p is either a const oop* or an oop*, depending 119 // on whether the associated storage is const or non-const, respectively. 120 // Then f(p) must be a valid expression. The result of invoking f(p) must 121 // be implicitly convertible to bool. Iteration terminates and returns 122 // false if any invocation of f returns false. Otherwise, the result of 123 // iteration is true. 124 // precondition: at safepoint. 125 template<typename F> inline bool iterate_safepoint(F f); 126 template<typename F> inline bool iterate_safepoint(F f) const; 127 128 // oops_do and weak_oops_do are wrappers around iterate_safepoint, providing 129 // an adaptation layer allowing the use of existing is-alive closures and 130 // OopClosures. Assume p is either const oop* or oop*, depending on whether 131 // the associated storage is const or non-const, respectively. Then 132 // 133 // - closure->do_oop(p) must be a valid expression whose value is ignored. 134 // 135 // - is_alive->do_object_b(*p) must be a valid expression whose value is 136 // convertible to bool. 137 // 138 // For weak_oops_do, if *p == NULL then neither is_alive nor closure will be 139 // invoked for p. If is_alive->do_object_b(*p) is false, then closure will 140 // not be invoked on p, and *p will be set to NULL. 141 142 template<typename Closure> inline void oops_do(Closure* closure); 143 template<typename Closure> inline void oops_do(Closure* closure) const; 144 template<typename Closure> inline void weak_oops_do(Closure* closure); 145 146 template<typename IsAliveClosure, typename Closure> 147 inline void weak_oops_do(IsAliveClosure* is_alive, Closure* closure); 148 149 // Parallel iteration is for the exclusive use of the GC. 150 // Other clients must use serial iteration. 151 template<bool concurrent, bool is_const> class ParState; 152 153 // Block cleanup functions are for the exclusive use of the GC. 154 // Both stop deleting if there is an in-progress concurrent iteration. 155 // Concurrent deletion locks both the _allocation_mutex and the _active_mutex. 156 void delete_empty_blocks_safepoint(); 157 void delete_empty_blocks_concurrent(); 158 159 // Debugging and logging support. 160 const char* name() const; 161 void print_on(outputStream* st) const PRODUCT_RETURN; 162 163 // Provides access to storage internals, for unit testing. 164 // Declare, but not define, the public class OopStorage::TestAccess. 165 // That class is defined as part of the unit-test. It "exports" the needed 166 // private types by providing public typedefs for them. 167 class TestAccess; 168 169 // xlC on AIX can't compile test_oopStorage.cpp with following private 170 // classes. C++03 introduced access for nested classes with DR45, but xlC 171 // version 12 rejects it. 172 NOT_AIX( private: ) 173 class Block; // Fixed-size array of oops, plus bookkeeping. 174 class ActiveArray; // Array of Blocks, plus bookkeeping. 175 class AllocationListEntry; // Provides AllocationList links in a Block. 176 177 // Doubly-linked list of Blocks. 178 class AllocationList { 179 const Block* _head; 180 const Block* _tail; 181 182 // Noncopyable. 183 AllocationList(const AllocationList&); 184 AllocationList& operator=(const AllocationList&); 185 186 public: 187 AllocationList(); 188 ~AllocationList(); 189 190 Block* head(); 191 Block* tail(); 192 const Block* chead() const; 193 const Block* ctail() const; 194 195 Block* prev(Block& block); 196 Block* next(Block& block); 197 198 const Block* prev(const Block& block) const; 199 const Block* next(const Block& block) const; 200 201 void push_front(const Block& block); 202 void push_back(const Block& block); 203 void unlink(const Block& block); 204 }; 205 206 // RCU-inspired protection of access to _active_array. 207 class ProtectActive { 208 volatile uint _enter; 209 volatile uint _exit[2]; 210 211 public: 212 ProtectActive(); 213 214 uint read_enter(); 215 void read_exit(uint enter_value); 216 void write_synchronize(); 217 }; 218 219 private: 220 const char* _name; 221 ActiveArray* _active_array; 222 AllocationList _allocation_list; 223 Block* volatile _deferred_updates; 224 225 Mutex* _allocation_mutex; 226 Mutex* _active_mutex; 227 228 // Volatile for racy unlocked accesses. 229 volatile size_t _allocation_count; 230 231 // Protection for _active_array. 232 mutable ProtectActive _protect_active; 233 234 // mutable because this gets set even for const iteration. 235 mutable bool _concurrent_iteration_active; 236 237 Block* find_block_or_null(const oop* ptr) const; 238 void delete_empty_block(const Block& block); 239 bool reduce_deferred_updates(); 240 241 // Managing _active_array. 242 bool expand_active_array(); 243 void replace_active_array(ActiveArray* new_array); 244 ActiveArray* obtain_active_array() const; 245 void relinquish_block_array(ActiveArray* array) const; 246 class WithActiveArray; // RAII helper for active array access. 247 248 template<typename F, typename Storage> 249 static bool iterate_impl(F f, Storage* storage); 250 251 // Implementation support for parallel iteration 252 class BasicParState; 253 254 // Wrapper for OopClosure-style function, so it can be used with 255 // iterate. Assume p is of type oop*. Then cl->do_oop(p) must be a 256 // valid expression whose value may be ignored. 257 template<typename Closure> class OopFn; 258 template<typename Closure> static OopFn<Closure> oop_fn(Closure* cl); 259 260 // Wrapper for BoolObjectClosure + iteration handler pair, so they 261 // can be used with iterate. 262 template<typename IsAlive, typename F> class IfAliveFn; 263 template<typename IsAlive, typename F> 264 static IfAliveFn<IsAlive, F> if_alive_fn(IsAlive* is_alive, F f); 265 266 // Wrapper for iteration handler, automatically skipping NULL entries. 267 template<typename F> class SkipNullFn; 268 template<typename F> static SkipNullFn<F> skip_null_fn(F f); 269 }; 270 271 #endif // include guard