1 /* 2 * Copyright (c) 2001, 2015, 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_GC_INTERFACE_COLLECTEDHEAP_HPP 26 #define SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP 27 28 #include "gc_interface/gcCause.hpp" 29 #include "gc_implementation/shared/gcWhen.hpp" 30 #include "memory/allocation.hpp" 31 #include "runtime/handles.hpp" 32 #include "runtime/perfData.hpp" 33 #include "runtime/safepoint.hpp" 34 #include "utilities/events.hpp" 35 36 // A "CollectedHeap" is an implementation of a java heap for HotSpot. This 37 // is an abstract class: there may be many different kinds of heaps. This 38 // class defines the functions that a heap must implement, and contains 39 // infrastructure common to all heaps. 40 41 class AdaptiveSizePolicy; 42 class BarrierSet; 43 class CollectorPolicy; 44 class GCHeapSummary; 45 class GCTimer; 46 class GCTracer; 47 class MetaspaceSummary; 48 class Thread; 49 class ThreadClosure; 50 class VirtualSpaceSummary; 51 class nmethod; 52 53 class GCMessage : public FormatBuffer<1024> { 54 public: 55 bool is_before; 56 57 public: 58 GCMessage() {} 59 }; 60 61 class GCHeapLog : public EventLogBase<GCMessage> { 62 private: 63 void log_heap(bool before); 64 65 public: 66 GCHeapLog() : EventLogBase<GCMessage>("GC Heap History") {} 67 68 void log_heap_before() { 69 log_heap(true); 70 } 71 void log_heap_after() { 72 log_heap(false); 73 } 74 }; 75 76 // 77 // CollectedHeap 78 // SharedHeap 79 // GenCollectedHeap 80 // G1CollectedHeap 81 // ParallelScavengeHeap 82 // 83 class CollectedHeap : public CHeapObj<mtInternal> { 84 friend class VMStructs; 85 friend class IsGCActiveMark; // Block structured external access to _is_gc_active 86 87 private: 88 #ifdef ASSERT 89 static int _fire_out_of_memory_count; 90 #endif 91 92 // Used for filler objects (static, but initialized in ctor). 93 static size_t _filler_array_max_size; 94 95 GCHeapLog* _gc_heap_log; 96 97 // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2 is being used 98 bool _defer_initial_card_mark; 99 100 MemRegion _reserved; 101 102 protected: 103 BarrierSet* _barrier_set; 104 bool _is_gc_active; 105 uint _n_par_threads; 106 107 unsigned int _total_collections; // ... started 108 unsigned int _total_full_collections; // ... started 109 NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;) 110 NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;) 111 112 // Reason for current garbage collection. Should be set to 113 // a value reflecting no collection between collections. 114 GCCause::Cause _gc_cause; 115 GCCause::Cause _gc_lastcause; 116 PerfStringVariable* _perf_gc_cause; 117 PerfStringVariable* _perf_gc_lastcause; 118 119 // Constructor 120 CollectedHeap(); 121 122 // Do common initializations that must follow instance construction, 123 // for example, those needing virtual calls. 124 // This code could perhaps be moved into initialize() but would 125 // be slightly more awkward because we want the latter to be a 126 // pure virtual. 127 void pre_initialize(); 128 129 // Create a new tlab. All TLAB allocations must go through this. 130 virtual HeapWord* allocate_new_tlab(size_t size); 131 132 // Accumulate statistics on all tlabs. 133 virtual void accumulate_statistics_all_tlabs(); 134 135 // Reinitialize tlabs before resuming mutators. 136 virtual void resize_all_tlabs(); 137 138 // Allocate from the current thread's TLAB, with broken-out slow path. 139 inline static HeapWord* allocate_from_tlab(KlassHandle klass, Thread* thread, size_t size); 140 static HeapWord* allocate_from_tlab_slow(KlassHandle klass, Thread* thread, size_t size); 141 142 // Allocate an uninitialized block of the given size, or returns NULL if 143 // this is impossible. 144 inline static HeapWord* common_mem_allocate_noinit(KlassHandle klass, size_t size, TRAPS); 145 146 // Like allocate_init, but the block returned by a successful allocation 147 // is guaranteed initialized to zeros. 148 inline static HeapWord* common_mem_allocate_init(KlassHandle klass, size_t size, TRAPS); 149 150 // Helper functions for (VM) allocation. 151 inline static void post_allocation_setup_common(KlassHandle klass, HeapWord* obj); 152 inline static void post_allocation_setup_no_klass_install(KlassHandle klass, 153 HeapWord* objPtr); 154 155 inline static void post_allocation_setup_obj(KlassHandle klass, HeapWord* obj, int size); 156 157 inline static void post_allocation_setup_array(KlassHandle klass, 158 HeapWord* obj, int length); 159 160 // Clears an allocated object. 161 inline static void init_obj(HeapWord* obj, size_t size); 162 163 // Filler object utilities. 164 static inline size_t filler_array_hdr_size(); 165 static inline size_t filler_array_min_size(); 166 167 DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);) 168 DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);) 169 170 // Fill with a single array; caller must ensure filler_array_min_size() <= 171 // words <= filler_array_max_size(). 172 static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true); 173 174 // Fill with a single object (either an int array or a java.lang.Object). 175 static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true); 176 177 virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer); 178 179 // Verification functions 180 virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size) 181 PRODUCT_RETURN; 182 virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size) 183 PRODUCT_RETURN; 184 debug_only(static void check_for_valid_allocation_state();) 185 186 public: 187 enum Name { 188 GenCollectedHeap, 189 ParallelScavengeHeap, 190 G1CollectedHeap 191 }; 192 193 static inline size_t filler_array_max_size() { 194 return _filler_array_max_size; 195 } 196 197 virtual Name kind() const = 0; 198 199 /** 200 * Returns JNI error code JNI_ENOMEM if memory could not be allocated, 201 * and JNI_OK on success. 202 */ 203 virtual jint initialize() = 0; 204 205 // In many heaps, there will be a need to perform some initialization activities 206 // after the Universe is fully formed, but before general heap allocation is allowed. 207 // This is the correct place to place such initialization methods. 208 virtual void post_initialize(); 209 210 // Stop any onging concurrent work and prepare for exit. 211 virtual void stop() {} 212 213 void initialize_reserved_region(HeapWord *start, HeapWord *end); 214 MemRegion reserved_region() const { return _reserved; } 215 address base() const { return (address)reserved_region().start(); } 216 217 virtual size_t capacity() const = 0; 218 virtual size_t used() const = 0; 219 220 // Return "true" if the part of the heap that allocates Java 221 // objects has reached the maximal committed limit that it can 222 // reach, without a garbage collection. 223 virtual bool is_maximal_no_gc() const = 0; 224 225 // Support for java.lang.Runtime.maxMemory(): return the maximum amount of 226 // memory that the vm could make available for storing 'normal' java objects. 227 // This is based on the reserved address space, but should not include space 228 // that the vm uses internally for bookkeeping or temporary storage 229 // (e.g., in the case of the young gen, one of the survivor 230 // spaces). 231 virtual size_t max_capacity() const = 0; 232 233 // Returns "TRUE" if "p" points into the reserved area of the heap. 234 bool is_in_reserved(const void* p) const { 235 return _reserved.contains(p); 236 } 237 238 bool is_in_reserved_or_null(const void* p) const { 239 return p == NULL || is_in_reserved(p); 240 } 241 242 // Returns "TRUE" iff "p" points into the committed areas of the heap. 243 // Since this method can be expensive in general, we restrict its 244 // use to assertion checking only. 245 virtual bool is_in(const void* p) const = 0; 246 247 bool is_in_or_null(const void* p) const { 248 return p == NULL || is_in(p); 249 } 250 251 bool is_in_place(Metadata** p) { 252 return !Universe::heap()->is_in(p); 253 } 254 bool is_in_place(oop* p) { return Universe::heap()->is_in(p); } 255 bool is_in_place(narrowOop* p) { 256 oop o = oopDesc::load_decode_heap_oop_not_null(p); 257 return Universe::heap()->is_in((const void*)o); 258 } 259 260 // Let's define some terms: a "closed" subset of a heap is one that 261 // 262 // 1) contains all currently-allocated objects, and 263 // 264 // 2) is closed under reference: no object in the closed subset 265 // references one outside the closed subset. 266 // 267 // Membership in a heap's closed subset is useful for assertions. 268 // Clearly, the entire heap is a closed subset, so the default 269 // implementation is to use "is_in_reserved". But this may not be too 270 // liberal to perform useful checking. Also, the "is_in" predicate 271 // defines a closed subset, but may be too expensive, since "is_in" 272 // verifies that its argument points to an object head. The 273 // "closed_subset" method allows a heap to define an intermediate 274 // predicate, allowing more precise checking than "is_in_reserved" at 275 // lower cost than "is_in." 276 277 // One important case is a heap composed of disjoint contiguous spaces, 278 // such as the Garbage-First collector. Such heaps have a convenient 279 // closed subset consisting of the allocated portions of those 280 // contiguous spaces. 281 282 // Return "TRUE" iff the given pointer points into the heap's defined 283 // closed subset (which defaults to the entire heap). 284 virtual bool is_in_closed_subset(const void* p) const { 285 return is_in_reserved(p); 286 } 287 288 bool is_in_closed_subset_or_null(const void* p) const { 289 return p == NULL || is_in_closed_subset(p); 290 } 291 292 // An object is scavengable if its location may move during a scavenge. 293 // (A scavenge is a GC which is not a full GC.) 294 virtual bool is_scavengable(const void *p) = 0; 295 296 void set_gc_cause(GCCause::Cause v) { 297 if (UsePerfData) { 298 _gc_lastcause = _gc_cause; 299 _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause)); 300 _perf_gc_cause->set_value(GCCause::to_string(v)); 301 } 302 _gc_cause = v; 303 } 304 GCCause::Cause gc_cause() { return _gc_cause; } 305 306 // Number of threads currently working on GC tasks. 307 uint n_par_threads() { return _n_par_threads; } 308 309 // May be overridden to set additional parallelism. 310 virtual void set_par_threads(uint t) { _n_par_threads = t; }; 311 312 // General obj/array allocation facilities. 313 inline static oop obj_allocate(KlassHandle klass, int size, TRAPS); 314 inline static oop array_allocate(KlassHandle klass, int size, int length, TRAPS); 315 inline static oop array_allocate_nozero(KlassHandle klass, int size, int length, TRAPS); 316 317 inline static void post_allocation_install_obj_klass(KlassHandle klass, 318 oop obj); 319 320 // Raw memory allocation facilities 321 // The obj and array allocate methods are covers for these methods. 322 // mem_allocate() should never be 323 // called to allocate TLABs, only individual objects. 324 virtual HeapWord* mem_allocate(size_t size, 325 bool* gc_overhead_limit_was_exceeded) = 0; 326 327 // Utilities for turning raw memory into filler objects. 328 // 329 // min_fill_size() is the smallest region that can be filled. 330 // fill_with_objects() can fill arbitrary-sized regions of the heap using 331 // multiple objects. fill_with_object() is for regions known to be smaller 332 // than the largest array of integers; it uses a single object to fill the 333 // region and has slightly less overhead. 334 static size_t min_fill_size() { 335 return size_t(align_object_size(oopDesc::header_size())); 336 } 337 338 static void fill_with_objects(HeapWord* start, size_t words, bool zap = true); 339 340 static void fill_with_object(HeapWord* start, size_t words, bool zap = true); 341 static void fill_with_object(MemRegion region, bool zap = true) { 342 fill_with_object(region.start(), region.word_size(), zap); 343 } 344 static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) { 345 fill_with_object(start, pointer_delta(end, start), zap); 346 } 347 348 // Return the address "addr" aligned by "alignment_in_bytes" if such 349 // an address is below "end". Return NULL otherwise. 350 inline static HeapWord* align_allocation_or_fail(HeapWord* addr, 351 HeapWord* end, 352 unsigned short alignment_in_bytes); 353 354 // Some heaps may offer a contiguous region for shared non-blocking 355 // allocation, via inlined code (by exporting the address of the top and 356 // end fields defining the extent of the contiguous allocation region.) 357 358 // This function returns "true" iff the heap supports this kind of 359 // allocation. (Default is "no".) 360 virtual bool supports_inline_contig_alloc() const { 361 return false; 362 } 363 // These functions return the addresses of the fields that define the 364 // boundaries of the contiguous allocation area. (These fields should be 365 // physically near to one another.) 366 virtual HeapWord** top_addr() const { 367 guarantee(false, "inline contiguous allocation not supported"); 368 return NULL; 369 } 370 virtual HeapWord** end_addr() const { 371 guarantee(false, "inline contiguous allocation not supported"); 372 return NULL; 373 } 374 375 // Some heaps may be in an unparseable state at certain times between 376 // collections. This may be necessary for efficient implementation of 377 // certain allocation-related activities. Calling this function before 378 // attempting to parse a heap ensures that the heap is in a parsable 379 // state (provided other concurrent activity does not introduce 380 // unparsability). It is normally expected, therefore, that this 381 // method is invoked with the world stopped. 382 // NOTE: if you override this method, make sure you call 383 // super::ensure_parsability so that the non-generational 384 // part of the work gets done. See implementation of 385 // CollectedHeap::ensure_parsability and, for instance, 386 // that of GenCollectedHeap::ensure_parsability(). 387 // The argument "retire_tlabs" controls whether existing TLABs 388 // are merely filled or also retired, thus preventing further 389 // allocation from them and necessitating allocation of new TLABs. 390 virtual void ensure_parsability(bool retire_tlabs); 391 392 // Section on thread-local allocation buffers (TLABs) 393 // If the heap supports thread-local allocation buffers, it should override 394 // the following methods: 395 // Returns "true" iff the heap supports thread-local allocation buffers. 396 // The default is "no". 397 virtual bool supports_tlab_allocation() const = 0; 398 399 // The amount of space available for thread-local allocation buffers. 400 virtual size_t tlab_capacity(Thread *thr) const = 0; 401 402 // The amount of used space for thread-local allocation buffers for the given thread. 403 virtual size_t tlab_used(Thread *thr) const = 0; 404 405 virtual size_t max_tlab_size() const; 406 407 // An estimate of the maximum allocation that could be performed 408 // for thread-local allocation buffers without triggering any 409 // collection or expansion activity. 410 virtual size_t unsafe_max_tlab_alloc(Thread *thr) const { 411 guarantee(false, "thread-local allocation buffers not supported"); 412 return 0; 413 } 414 415 // Can a compiler initialize a new object without store barriers? 416 // This permission only extends from the creation of a new object 417 // via a TLAB up to the first subsequent safepoint. If such permission 418 // is granted for this heap type, the compiler promises to call 419 // defer_store_barrier() below on any slow path allocation of 420 // a new object for which such initializing store barriers will 421 // have been elided. 422 virtual bool can_elide_tlab_store_barriers() const = 0; 423 424 // If a compiler is eliding store barriers for TLAB-allocated objects, 425 // there is probably a corresponding slow path which can produce 426 // an object allocated anywhere. The compiler's runtime support 427 // promises to call this function on such a slow-path-allocated 428 // object before performing initializations that have elided 429 // store barriers. Returns new_obj, or maybe a safer copy thereof. 430 virtual oop new_store_pre_barrier(JavaThread* thread, oop new_obj); 431 432 // Answers whether an initializing store to a new object currently 433 // allocated at the given address doesn't need a store 434 // barrier. Returns "true" if it doesn't need an initializing 435 // store barrier; answers "false" if it does. 436 virtual bool can_elide_initializing_store_barrier(oop new_obj) = 0; 437 438 // If a compiler is eliding store barriers for TLAB-allocated objects, 439 // we will be informed of a slow-path allocation by a call 440 // to new_store_pre_barrier() above. Such a call precedes the 441 // initialization of the object itself, and no post-store-barriers will 442 // be issued. Some heap types require that the barrier strictly follows 443 // the initializing stores. (This is currently implemented by deferring the 444 // barrier until the next slow-path allocation or gc-related safepoint.) 445 // This interface answers whether a particular heap type needs the card 446 // mark to be thus strictly sequenced after the stores. 447 virtual bool card_mark_must_follow_store() const = 0; 448 449 // If the CollectedHeap was asked to defer a store barrier above, 450 // this informs it to flush such a deferred store barrier to the 451 // remembered set. 452 virtual void flush_deferred_store_barrier(JavaThread* thread); 453 454 // Does this heap support heap inspection (+PrintClassHistogram?) 455 virtual bool supports_heap_inspection() const = 0; 456 457 // Perform a collection of the heap; intended for use in implementing 458 // "System.gc". This probably implies as full a collection as the 459 // "CollectedHeap" supports. 460 virtual void collect(GCCause::Cause cause) = 0; 461 462 // Perform a full collection 463 virtual void do_full_collection(bool clear_all_soft_refs) = 0; 464 465 // This interface assumes that it's being called by the 466 // vm thread. It collects the heap assuming that the 467 // heap lock is already held and that we are executing in 468 // the context of the vm thread. 469 virtual void collect_as_vm_thread(GCCause::Cause cause); 470 471 // Returns the barrier set for this heap 472 BarrierSet* barrier_set() { return _barrier_set; } 473 void set_barrier_set(BarrierSet* barrier_set); 474 475 // Returns "true" iff there is a stop-world GC in progress. (I assume 476 // that it should answer "false" for the concurrent part of a concurrent 477 // collector -- dld). 478 bool is_gc_active() const { return _is_gc_active; } 479 480 // Total number of GC collections (started) 481 unsigned int total_collections() const { return _total_collections; } 482 unsigned int total_full_collections() const { return _total_full_collections;} 483 484 // Increment total number of GC collections (started) 485 // Should be protected but used by PSMarkSweep - cleanup for 1.4.2 486 void increment_total_collections(bool full = false) { 487 _total_collections++; 488 if (full) { 489 increment_total_full_collections(); 490 } 491 } 492 493 void increment_total_full_collections() { _total_full_collections++; } 494 495 // Return the AdaptiveSizePolicy for the heap. 496 virtual AdaptiveSizePolicy* size_policy() = 0; 497 498 // Return the CollectorPolicy for the heap 499 virtual CollectorPolicy* collector_policy() const = 0; 500 501 // Iterate over all objects, calling "cl.do_object" on each. 502 virtual void object_iterate(ObjectClosure* cl) = 0; 503 504 // Similar to object_iterate() except iterates only 505 // over live objects. 506 virtual void safe_object_iterate(ObjectClosure* cl) = 0; 507 508 // NOTE! There is no requirement that a collector implement these 509 // functions. 510 // 511 // A CollectedHeap is divided into a dense sequence of "blocks"; that is, 512 // each address in the (reserved) heap is a member of exactly 513 // one block. The defining characteristic of a block is that it is 514 // possible to find its size, and thus to progress forward to the next 515 // block. (Blocks may be of different sizes.) Thus, blocks may 516 // represent Java objects, or they might be free blocks in a 517 // free-list-based heap (or subheap), as long as the two kinds are 518 // distinguishable and the size of each is determinable. 519 520 // Returns the address of the start of the "block" that contains the 521 // address "addr". We say "blocks" instead of "object" since some heaps 522 // may not pack objects densely; a chunk may either be an object or a 523 // non-object. 524 virtual HeapWord* block_start(const void* addr) const = 0; 525 526 // Requires "addr" to be the start of a chunk, and returns its size. 527 // "addr + size" is required to be the start of a new chunk, or the end 528 // of the active area of the heap. 529 virtual size_t block_size(const HeapWord* addr) const = 0; 530 531 // Requires "addr" to be the start of a block, and returns "TRUE" iff 532 // the block is an object. 533 virtual bool block_is_obj(const HeapWord* addr) const = 0; 534 535 // Returns the longest time (in ms) that has elapsed since the last 536 // time that any part of the heap was examined by a garbage collection. 537 virtual jlong millis_since_last_gc() = 0; 538 539 // Perform any cleanup actions necessary before allowing a verification. 540 virtual void prepare_for_verify() = 0; 541 542 // Generate any dumps preceding or following a full gc 543 void pre_full_gc_dump(GCTimer* timer); 544 void post_full_gc_dump(GCTimer* timer); 545 546 VirtualSpaceSummary create_heap_space_summary(); 547 GCHeapSummary create_heap_summary(); 548 549 MetaspaceSummary create_metaspace_summary(); 550 551 // Print heap information on the given outputStream. 552 virtual void print_on(outputStream* st) const = 0; 553 // The default behavior is to call print_on() on tty. 554 virtual void print() const { 555 print_on(tty); 556 } 557 // Print more detailed heap information on the given 558 // outputStream. The default behavior is to call print_on(). It is 559 // up to each subclass to override it and add any additional output 560 // it needs. 561 virtual void print_extended_on(outputStream* st) const { 562 print_on(st); 563 } 564 565 virtual void print_on_error(outputStream* st) const; 566 567 // Print all GC threads (other than the VM thread) 568 // used by this heap. 569 virtual void print_gc_threads_on(outputStream* st) const = 0; 570 // The default behavior is to call print_gc_threads_on() on tty. 571 void print_gc_threads() { 572 print_gc_threads_on(tty); 573 } 574 // Iterator for all GC threads (other than VM thread) 575 virtual void gc_threads_do(ThreadClosure* tc) const = 0; 576 577 // Print any relevant tracing info that flags imply. 578 // Default implementation does nothing. 579 virtual void print_tracing_info() const = 0; 580 581 void print_heap_before_gc(); 582 void print_heap_after_gc(); 583 584 // Registering and unregistering an nmethod (compiled code) with the heap. 585 // Override with specific mechanism for each specialized heap type. 586 virtual void register_nmethod(nmethod* nm); 587 virtual void unregister_nmethod(nmethod* nm); 588 589 void trace_heap_before_gc(const GCTracer* gc_tracer); 590 void trace_heap_after_gc(const GCTracer* gc_tracer); 591 592 // Heap verification 593 virtual void verify(bool silent, VerifyOption option) = 0; 594 595 // Non product verification and debugging. 596 #ifndef PRODUCT 597 // Support for PromotionFailureALot. Return true if it's time to cause a 598 // promotion failure. The no-argument version uses 599 // this->_promotion_failure_alot_count as the counter. 600 inline bool promotion_should_fail(volatile size_t* count); 601 inline bool promotion_should_fail(); 602 603 // Reset the PromotionFailureALot counters. Should be called at the end of a 604 // GC in which promotion failure occurred. 605 inline void reset_promotion_should_fail(volatile size_t* count); 606 inline void reset_promotion_should_fail(); 607 #endif // #ifndef PRODUCT 608 609 #ifdef ASSERT 610 static int fired_fake_oom() { 611 return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt); 612 } 613 #endif 614 615 public: 616 // This is a convenience method that is used in cases where 617 // the actual number of GC worker threads is not pertinent but 618 // only whether there more than 0. Use of this method helps 619 // reduce the occurrence of ParallelGCThreads to uses where the 620 // actual number may be germane. 621 static bool use_parallel_gc_threads() { return ParallelGCThreads > 0; } 622 623 // Copy the current allocation context statistics for the specified contexts. 624 // For each context in contexts, set the corresponding entries in the totals 625 // and accuracy arrays to the current values held by the statistics. Each 626 // array should be of length len. 627 // Returns true if there are more stats available. 628 virtual bool copy_allocation_context_stats(const jint* contexts, 629 jlong* totals, 630 jbyte* accuracy, 631 jint len) { 632 return false; 633 } 634 635 /////////////// Unit tests /////////////// 636 637 NOT_PRODUCT(static void test_is_in();) 638 }; 639 640 // Class to set and reset the GC cause for a CollectedHeap. 641 642 class GCCauseSetter : StackObj { 643 CollectedHeap* _heap; 644 GCCause::Cause _previous_cause; 645 public: 646 GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) { 647 assert(SafepointSynchronize::is_at_safepoint(), 648 "This method manipulates heap state without locking"); 649 _heap = heap; 650 _previous_cause = _heap->gc_cause(); 651 _heap->set_gc_cause(cause); 652 } 653 654 ~GCCauseSetter() { 655 assert(SafepointSynchronize::is_at_safepoint(), 656 "This method manipulates heap state without locking"); 657 _heap->set_gc_cause(_previous_cause); 658 } 659 }; 660 661 #endif // SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP