1 /*
  2  * Copyright (c) 2013, 2021, Red Hat, Inc. All rights reserved.
  3  * Copyright (C) 2022 THL A29 Limited, a Tencent company. All rights reserved.
  4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  5  *
  6  * This code is free software; you can redistribute it and/or modify it
  7  * under the terms of the GNU General Public License version 2 only, as
  8  * published by the Free Software Foundation.
  9  *
 10  * This code is distributed in the hope that it will be useful, but WITHOUT
 11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 13  * version 2 for more details (a copy is included in the LICENSE file that
 14  * accompanied this code).
 15  *
 16  * You should have received a copy of the GNU General Public License version
 17  * 2 along with this work; if not, write to the Free Software Foundation,
 18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 19  *
 20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 21  * or visit www.oracle.com if you need additional information or have any
 22  * questions.
 23  *
 24  */
 25 
 26 #include "precompiled.hpp"
 27 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
 28 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
 29 #include "gc/shenandoah/shenandoahControlThread.hpp"
 30 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
 31 #include "gc/shenandoah/shenandoahFreeSet.hpp"
 32 #include "gc/shenandoah/shenandoahFullGC.hpp"
 33 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
 34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
 35 #include "gc/shenandoah/shenandoahMark.inline.hpp"
 36 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
 37 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
 38 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
 39 #include "gc/shenandoah/shenandoahUtils.hpp"
 40 #include "gc/shenandoah/shenandoahVMOperations.hpp"
 41 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
 42 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
 43 #include "memory/iterator.hpp"
 44 #include "memory/metaspaceUtils.hpp"
 45 #include "memory/metaspaceStats.hpp"
 46 #include "memory/universe.hpp"
 47 #include "runtime/atomic.hpp"
 48 
 49 ShenandoahControlThread::ShenandoahControlThread() :
 50   ConcurrentGCThread(),
 51   _alloc_failure_waiters_lock(Mutex::safepoint-1, "ShenandoahAllocFailureGC_lock", true),
 52   _gc_waiters_lock(Mutex::safepoint-1, "ShenandoahRequestedGC_lock", true),
 53   _periodic_task(this),
 54   _requested_gc_cause(GCCause::_no_cause_specified),
 55   _degen_point(ShenandoahGC::_degenerated_outside_cycle),
 56   _allocs_seen(0) {
 57 
 58   reset_gc_id();
 59   create_and_start();
 60   _periodic_task.enroll();
 61   if (ShenandoahPacing) {
 62     _periodic_pacer_notify_task.enroll();
 63   }
 64 }
 65 
 66 ShenandoahControlThread::~ShenandoahControlThread() {
 67   // This is here so that super is called.
 68 }
 69 
 70 void ShenandoahPeriodicTask::task() {
 71   _thread->handle_force_counters_update();
 72   _thread->handle_counters_update();
 73 }
 74 
 75 void ShenandoahPeriodicPacerNotify::task() {
 76   assert(ShenandoahPacing, "Should not be here otherwise");
 77   ShenandoahHeap::heap()->pacer()->notify_waiters();
 78 }
 79 
 80 void ShenandoahControlThread::run_service() {
 81   ShenandoahHeap* heap = ShenandoahHeap::heap();
 82 
 83   GCMode default_mode = concurrent_normal;
 84   GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
 85   int sleep = ShenandoahControlIntervalMin;
 86 
 87   double last_shrink_time = os::elapsedTime();
 88   double last_sleep_adjust_time = os::elapsedTime();
 89 
 90   // Shrink period avoids constantly polling regions for shrinking.
 91   // Having a period 10x lower than the delay would mean we hit the
 92   // shrinking with lag of less than 1/10-th of true delay.
 93   // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
 94   double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
 95 
 96   ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
 97   ShenandoahHeuristics* heuristics = heap->heuristics();
 98   while (!in_graceful_shutdown() && !should_terminate()) {
 99     // Figure out if we have pending requests.
100     bool alloc_failure_pending = _alloc_failure_gc.is_set();
101     bool is_gc_requested = _gc_requested.is_set();
102     GCCause::Cause requested_gc_cause = _requested_gc_cause;
103     bool explicit_gc_requested = is_gc_requested && is_explicit_gc(requested_gc_cause);
104     bool implicit_gc_requested = is_gc_requested && !is_explicit_gc(requested_gc_cause);
105 
106     // This control loop iteration have seen this much allocations.
107     size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0, memory_order_relaxed);
108 
109     // Check if we have seen a new target for soft max heap size.
110     bool soft_max_changed = check_soft_max_changed();
111 
112     // Choose which GC mode to run in. The block below should select a single mode.
113     GCMode mode = none;
114     GCCause::Cause cause = GCCause::_last_gc_cause;
115     ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
116 
117     if (alloc_failure_pending) {
118       // Allocation failure takes precedence: we have to deal with it first thing
119       log_info(gc)("Trigger: Handle Allocation Failure");
120 
121       cause = GCCause::_allocation_failure;
122 
123       // Consume the degen point, and seed it with default value
124       degen_point = _degen_point;
125       _degen_point = ShenandoahGC::_degenerated_outside_cycle;
126 
127       if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle()) {
128         heuristics->record_allocation_failure_gc();
129         policy->record_alloc_failure_to_degenerated(degen_point);
130         mode = stw_degenerated;
131       } else {
132         heuristics->record_allocation_failure_gc();
133         policy->record_alloc_failure_to_full();
134         mode = stw_full;
135       }
136 
137     } else if (explicit_gc_requested) {
138       cause = requested_gc_cause;
139       log_info(gc)("Trigger: Explicit GC request (%s)", GCCause::to_string(cause));
140 
141       heuristics->record_requested_gc();
142 
143       if (ExplicitGCInvokesConcurrent) {
144         policy->record_explicit_to_concurrent();
145         mode = default_mode;
146         // Unload and clean up everything
147         heap->set_unload_classes(heuristics->can_unload_classes());
148       } else {
149         policy->record_explicit_to_full();
150         mode = stw_full;
151       }
152     } else if (implicit_gc_requested) {
153       cause = requested_gc_cause;
154       log_info(gc)("Trigger: Implicit GC request (%s)", GCCause::to_string(cause));
155 
156       heuristics->record_requested_gc();
157 
158       if (ShenandoahImplicitGCInvokesConcurrent) {
159         policy->record_implicit_to_concurrent();
160         mode = default_mode;
161 
162         // Unload and clean up everything
163         heap->set_unload_classes(heuristics->can_unload_classes());
164       } else {
165         policy->record_implicit_to_full();
166         mode = stw_full;
167       }
168     } else {
169       // Potential normal cycle: ask heuristics if it wants to act
170       if (heuristics->should_start_gc()) {
171         mode = default_mode;
172         cause = default_cause;
173       }
174 
175       // Ask policy if this cycle wants to process references or unload classes
176       heap->set_unload_classes(heuristics->should_unload_classes());
177     }
178 
179     // Blow all soft references on this cycle, if handling allocation failure,
180     // either implicit or explicit GC request,  or we are requested to do so unconditionally.
181     if (alloc_failure_pending || implicit_gc_requested || explicit_gc_requested || ShenandoahAlwaysClearSoftRefs) {
182       heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
183     }
184 
185     bool gc_requested = (mode != none);
186     assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
187 
188     if (gc_requested) {
189       // GC is starting, bump the internal ID
190       update_gc_id();
191 
192       heap->reset_bytes_allocated_since_gc_start();
193 
194       MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
195 
196       // If GC was requested, we are sampling the counters even without actual triggers
197       // from allocation machinery. This captures GC phases more accurately.
198       set_forced_counters_update(true);
199 
200       // If GC was requested, we better dump freeset data for performance debugging
201       {
202         ShenandoahHeapLocker locker(heap->lock());
203         heap->free_set()->log_status();
204       }
205 
206       switch (mode) {
207         case concurrent_normal:
208           service_concurrent_normal_cycle(cause);
209           break;
210         case stw_degenerated:
211           service_stw_degenerated_cycle(cause, degen_point);
212           break;
213         case stw_full:
214           service_stw_full_cycle(cause);
215           break;
216         default:
217           ShouldNotReachHere();
218       }
219 
220       // If this was the requested GC cycle, notify waiters about it
221       if (explicit_gc_requested || implicit_gc_requested) {
222         notify_gc_waiters();
223       }
224 
225       // If this was the allocation failure GC cycle, notify waiters about it
226       if (alloc_failure_pending) {
227         notify_alloc_failure_waiters();
228       }
229 
230       // Report current free set state at the end of cycle, whether
231       // it is a normal completion, or the abort.
232       {
233         ShenandoahHeapLocker locker(heap->lock());
234         heap->free_set()->log_status();
235 
236         // Notify Universe about new heap usage. This has implications for
237         // global soft refs policy, and we better report it every time heap
238         // usage goes down.
239         Universe::heap()->update_capacity_and_used_at_gc();
240 
241         // Signal that we have completed a visit to all live objects.
242         Universe::heap()->record_whole_heap_examined_timestamp();
243       }
244 
245       // Disable forced counters update, and update counters one more time
246       // to capture the state at the end of GC session.
247       handle_force_counters_update();
248       set_forced_counters_update(false);
249 
250       // Retract forceful part of soft refs policy
251       heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
252 
253       // Clear metaspace oom flag, if current cycle unloaded classes
254       if (heap->unload_classes()) {
255         heuristics->clear_metaspace_oom();
256       }
257 
258       // Commit worker statistics to cycle data
259       heap->phase_timings()->flush_par_workers_to_cycle();
260       if (ShenandoahPacing) {
261         heap->pacer()->flush_stats_to_cycle();
262       }
263 
264       // Print GC stats for current cycle
265       {
266         LogTarget(Info, gc, stats) lt;
267         if (lt.is_enabled()) {
268           ResourceMark rm;
269           LogStream ls(lt);
270           heap->phase_timings()->print_cycle_on(&ls);
271           if (ShenandoahPacing) {
272             heap->pacer()->print_cycle_on(&ls);
273           }
274         }
275       }
276 
277       // Commit statistics to globals
278       heap->phase_timings()->flush_cycle_to_global();
279 
280       // Print Metaspace change following GC (if logging is enabled).
281       MetaspaceUtils::print_metaspace_change(meta_sizes);
282 
283       // GC is over, we are at idle now
284       if (ShenandoahPacing) {
285         heap->pacer()->setup_for_idle();
286       }
287     } else {
288       // Allow allocators to know we have seen this much regions
289       if (ShenandoahPacing && (allocs_seen > 0)) {
290         heap->pacer()->report_alloc(allocs_seen);
291       }
292     }
293 
294     double current = os::elapsedTime();
295 
296     if (ShenandoahUncommit && (explicit_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
297       // Explicit GC tries to uncommit everything down to min capacity.
298       // Soft max change tries to uncommit everything down to target capacity.
299       // Periodic uncommit tries to uncommit suitable regions down to min capacity.
300 
301       double shrink_before = (explicit_gc_requested || soft_max_changed) ?
302                              current :
303                              current - (ShenandoahUncommitDelay / 1000.0);
304 
305       size_t shrink_until = soft_max_changed ?
306                              heap->soft_max_capacity() :
307                              heap->min_capacity();
308 
309       service_uncommit(shrink_before, shrink_until);
310       heap->phase_timings()->flush_cycle_to_global();
311       last_shrink_time = current;
312     }
313 
314     // Wait before performing the next action. If allocation happened during this wait,
315     // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
316     // back off exponentially.
317     if (_heap_changed.try_unset()) {
318       sleep = ShenandoahControlIntervalMin;
319     } else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
320       sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
321       last_sleep_adjust_time = current;
322     }
323     os::naked_short_sleep(sleep);
324   }
325 
326   // Wait for the actual stop(), can't leave run_service() earlier.
327   while (!should_terminate()) {
328     os::naked_short_sleep(ShenandoahControlIntervalMin);
329   }
330 }
331 
332 bool ShenandoahControlThread::check_soft_max_changed() const {
333   ShenandoahHeap* heap = ShenandoahHeap::heap();
334   size_t new_soft_max = Atomic::load(&SoftMaxHeapSize);
335   size_t old_soft_max = heap->soft_max_capacity();
336   if (new_soft_max != old_soft_max) {
337     new_soft_max = MAX2(heap->min_capacity(), new_soft_max);
338     new_soft_max = MIN2(heap->max_capacity(), new_soft_max);
339     if (new_soft_max != old_soft_max) {
340       log_info(gc)("Soft Max Heap Size: " SIZE_FORMAT "%s -> " SIZE_FORMAT "%s",
341                    byte_size_in_proper_unit(old_soft_max), proper_unit_for_byte_size(old_soft_max),
342                    byte_size_in_proper_unit(new_soft_max), proper_unit_for_byte_size(new_soft_max)
343       );
344       heap->set_soft_max_capacity(new_soft_max);
345       return true;
346     }
347   }
348   return false;
349 }
350 
351 void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
352   // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
353   // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
354   // If second allocation failure happens during Degenerated GC cycle (for example, when GC
355   // tries to evac something and no memory is available), cycle degrades to Full GC.
356   //
357   // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
358   // heuristics says there are no regions to compact, and all the collection comes from immediately
359   // reclaimable regions.
360   //
361   // ................................................................................................
362   //
363   //                                    (immediate garbage shortcut)                Concurrent GC
364   //                             /-------------------------------------------\
365   //                             |                                           |
366   //                             |                                           |
367   //                             |                                           |
368   //                             |                                           v
369   // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
370   //                   |                    |                 |              ^
371   //                   | (af)               | (af)            | (af)         |
372   // ..................|....................|.................|..............|.......................
373   //                   |                    |                 |              |
374   //                   |                    |                 |              |      Degenerated GC
375   //                   v                    v                 v              |
376   //               STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
377   //                   |                    |                 |              ^
378   //                   | (af)               | (af)            | (af)         |
379   // ..................|....................|.................|..............|.......................
380   //                   |                    |                 |              |
381   //                   |                    v                 |              |      Full GC
382   //                   \------------------->o<----------------/              |
383   //                                        |                                |
384   //                                        v                                |
385   //                                      Full GC  --------------------------/
386   //
387   ShenandoahHeap* heap = ShenandoahHeap::heap();
388   if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
389 
390   GCIdMark gc_id_mark;
391   ShenandoahGCSession session(cause);
392 
393   TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
394 
395   ShenandoahConcurrentGC gc;
396   if (gc.collect(cause)) {
397     // Cycle is complete
398     heap->heuristics()->record_success_concurrent();
399     heap->shenandoah_policy()->record_success_concurrent();
400   } else {
401     assert(heap->cancelled_gc(), "Must have been cancelled");
402     check_cancellation_or_degen(gc.degen_point());
403   }
404 }
405 
406 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
407   ShenandoahHeap* heap = ShenandoahHeap::heap();
408   if (heap->cancelled_gc()) {
409     assert (is_alloc_failure_gc() || in_graceful_shutdown(), "Cancel GC either for alloc failure GC, or gracefully exiting");
410     if (!in_graceful_shutdown()) {
411       assert (_degen_point == ShenandoahGC::_degenerated_outside_cycle,
412               "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
413       _degen_point = point;
414     }
415     return true;
416   }
417   return false;
418 }
419 
420 void ShenandoahControlThread::stop_service() {
421   // Nothing to do here.
422 }
423 
424 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
425   GCIdMark gc_id_mark;
426   ShenandoahGCSession session(cause);
427 
428   ShenandoahFullGC gc;
429   gc.collect(cause);
430 
431   ShenandoahHeap* const heap = ShenandoahHeap::heap();
432   heap->heuristics()->record_success_full();
433   heap->shenandoah_policy()->record_success_full();
434 }
435 
436 void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
437   assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
438 
439   GCIdMark gc_id_mark;
440   ShenandoahGCSession session(cause);
441 
442   ShenandoahDegenGC gc(point);
443   gc.collect(cause);
444 
445   ShenandoahHeap* const heap = ShenandoahHeap::heap();
446   heap->heuristics()->record_success_degenerated();
447   heap->shenandoah_policy()->record_success_degenerated();
448 }
449 
450 void ShenandoahControlThread::service_uncommit(double shrink_before, size_t shrink_until) {
451   ShenandoahHeap* heap = ShenandoahHeap::heap();
452 
453   // Determine if there is work to do. This avoids taking heap lock if there is
454   // no work available, avoids spamming logs with superfluous logging messages,
455   // and minimises the amount of work while locks are taken.
456 
457   if (heap->committed() <= shrink_until) return;
458 
459   bool has_work = false;
460   for (size_t i = 0; i < heap->num_regions(); i++) {
461     ShenandoahHeapRegion *r = heap->get_region(i);
462     if (r->is_empty_committed() && (r->empty_time() < shrink_before)) {
463       has_work = true;
464       break;
465     }
466   }
467 
468   if (has_work) {
469     heap->entry_uncommit(shrink_before, shrink_until);
470   }
471 }
472 
473 bool ShenandoahControlThread::is_explicit_gc(GCCause::Cause cause) const {
474   return GCCause::is_user_requested_gc(cause) ||
475          GCCause::is_serviceability_requested_gc(cause);
476 }
477 
478 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
479   assert(GCCause::is_user_requested_gc(cause) ||
480          GCCause::is_serviceability_requested_gc(cause) ||
481          cause == GCCause::_metadata_GC_clear_soft_refs ||
482          cause == GCCause::_codecache_GC_threshold ||
483          cause == GCCause::_full_gc_alot ||
484          cause == GCCause::_wb_full_gc ||
485          cause == GCCause::_wb_breakpoint ||
486          cause == GCCause::_scavenge_alot,
487          "only requested GCs here");
488 
489   if (is_explicit_gc(cause)) {
490     if (!DisableExplicitGC) {
491       handle_requested_gc(cause);
492     }
493   } else {
494     handle_requested_gc(cause);
495   }
496 }
497 
498 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
499   // Make sure we have at least one complete GC cycle before unblocking
500   // from the explicit GC request.
501   //
502   // This is especially important for weak references cleanup and/or native
503   // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
504   // comes very late in the already running cycle, it would miss lots of new
505   // opportunities for cleanup that were made available before the caller
506   // requested the GC.
507 
508   MonitorLocker ml(&_gc_waiters_lock);
509   size_t current_gc_id = get_gc_id();
510   size_t required_gc_id = current_gc_id + 1;
511   while (current_gc_id < required_gc_id) {
512     // Although setting gc request is under _gc_waiters_lock, but read side (run_service())
513     // does not take the lock. We need to enforce following order, so that read side sees
514     // latest requested gc cause when the flag is set.
515     _requested_gc_cause = cause;
516     _gc_requested.set();
517 
518     if (cause != GCCause::_wb_breakpoint) {
519       ml.wait();
520     }
521     current_gc_id = get_gc_id();
522   }
523 }
524 
525 void ShenandoahControlThread::handle_alloc_failure(ShenandoahAllocRequest& req) {
526   ShenandoahHeap* heap = ShenandoahHeap::heap();
527 
528   assert(current()->is_Java_thread(), "expect Java thread here");
529 
530   if (try_set_alloc_failure_gc()) {
531     // Only report the first allocation failure
532     log_info(gc)("Failed to allocate %s, " SIZE_FORMAT "%s",
533                  req.type_string(),
534                  byte_size_in_proper_unit(req.size() * HeapWordSize), proper_unit_for_byte_size(req.size() * HeapWordSize));
535 
536     // Now that alloc failure GC is scheduled, we can abort everything else
537     heap->cancel_gc(GCCause::_allocation_failure);
538   }
539 
540   MonitorLocker ml(&_alloc_failure_waiters_lock);
541   while (is_alloc_failure_gc()) {
542     ml.wait();
543   }
544 }
545 
546 void ShenandoahControlThread::handle_alloc_failure_evac(size_t words) {
547   ShenandoahHeap* heap = ShenandoahHeap::heap();
548 
549   if (try_set_alloc_failure_gc()) {
550     // Only report the first allocation failure
551     log_info(gc)("Failed to allocate " SIZE_FORMAT "%s for evacuation",
552                  byte_size_in_proper_unit(words * HeapWordSize), proper_unit_for_byte_size(words * HeapWordSize));
553   }
554 
555   // Forcefully report allocation failure
556   heap->cancel_gc(GCCause::_shenandoah_allocation_failure_evac);
557 }
558 
559 void ShenandoahControlThread::notify_alloc_failure_waiters() {
560   _alloc_failure_gc.unset();
561   MonitorLocker ml(&_alloc_failure_waiters_lock);
562   ml.notify_all();
563 }
564 
565 bool ShenandoahControlThread::try_set_alloc_failure_gc() {
566   return _alloc_failure_gc.try_set();
567 }
568 
569 bool ShenandoahControlThread::is_alloc_failure_gc() {
570   return _alloc_failure_gc.is_set();
571 }
572 
573 void ShenandoahControlThread::notify_gc_waiters() {
574   _gc_requested.unset();
575   MonitorLocker ml(&_gc_waiters_lock);
576   ml.notify_all();
577 }
578 
579 void ShenandoahControlThread::handle_counters_update() {
580   if (_do_counters_update.is_set()) {
581     _do_counters_update.unset();
582     ShenandoahHeap::heap()->monitoring_support()->update_counters();
583   }
584 }
585 
586 void ShenandoahControlThread::handle_force_counters_update() {
587   if (_force_counters_update.is_set()) {
588     _do_counters_update.unset(); // reset these too, we do update now!
589     ShenandoahHeap::heap()->monitoring_support()->update_counters();
590   }
591 }
592 
593 void ShenandoahControlThread::notify_heap_changed() {
594   // This is called from allocation path, and thus should be fast.
595 
596   // Update monitoring counters when we took a new region. This amortizes the
597   // update costs on slow path.
598   if (_do_counters_update.is_unset()) {
599     _do_counters_update.set();
600   }
601   // Notify that something had changed.
602   if (_heap_changed.is_unset()) {
603     _heap_changed.set();
604   }
605 }
606 
607 void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
608   assert(ShenandoahPacing, "should only call when pacing is enabled");
609   Atomic::add(&_allocs_seen, words, memory_order_relaxed);
610 }
611 
612 void ShenandoahControlThread::set_forced_counters_update(bool value) {
613   _force_counters_update.set_cond(value);
614 }
615 
616 void ShenandoahControlThread::reset_gc_id() {
617   Atomic::store(&_gc_id, (size_t)0);
618 }
619 
620 void ShenandoahControlThread::update_gc_id() {
621   Atomic::inc(&_gc_id);
622 }
623 
624 size_t ShenandoahControlThread::get_gc_id() {
625   return Atomic::load(&_gc_id);
626 }
627 
628 void ShenandoahControlThread::print() const {
629   print_on(tty);
630 }
631 
632 void ShenandoahControlThread::print_on(outputStream* st) const {
633   st->print("Shenandoah Concurrent Thread");
634   Thread::print_on(st);
635   st->cr();
636 }
637 
638 void ShenandoahControlThread::start() {
639   create_and_start();
640 }
641 
642 void ShenandoahControlThread::prepare_for_graceful_shutdown() {
643   _graceful_shutdown.set();
644 }
645 
646 bool ShenandoahControlThread::in_graceful_shutdown() {
647   return _graceful_shutdown.is_set();
648 }