< prev index next >

src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp

Print this page
@@ -27,34 +27,42 @@
  #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
  #include "gc/shenandoah/shenandoahControlThread.hpp"
  #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
  #include "gc/shenandoah/shenandoahFreeSet.hpp"
  #include "gc/shenandoah/shenandoahFullGC.hpp"
+ #include "gc/shenandoah/shenandoahGeneration.hpp"
+ #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
  #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
  #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  #include "gc/shenandoah/shenandoahMark.inline.hpp"
  #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
  #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
+ #include "gc/shenandoah/shenandoahOldGC.hpp"
  #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
  #include "gc/shenandoah/shenandoahUtils.hpp"
  #include "gc/shenandoah/shenandoahVMOperations.hpp"
  #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
  #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
+ #include "gc/shenandoah/mode/shenandoahMode.hpp"
  #include "memory/iterator.hpp"
  #include "memory/metaspaceUtils.hpp"
  #include "memory/metaspaceStats.hpp"
  #include "memory/universe.hpp"
  #include "runtime/atomic.hpp"
  
  ShenandoahControlThread::ShenandoahControlThread() :
    ConcurrentGCThread(),
    _alloc_failure_waiters_lock(Mutex::leaf, "ShenandoahAllocFailureGC_lock", Monitor::_safepoint_check_always, true),
    _gc_waiters_lock(Mutex::leaf, "ShenandoahRequestedGC_lock", Monitor::_safepoint_check_always, true),
+   _control_lock(Mutex::leaf - 1, "ShenandoahControlGC_lock", Monitor::_safepoint_check_never, true),
    _periodic_task(this),
    _requested_gc_cause(GCCause::_no_cause_specified),
+   _requested_generation(GenerationMode::GLOBAL),
    _degen_point(ShenandoahGC::_degenerated_outside_cycle),
-   _allocs_seen(0) {
+   _degen_generation(NULL),
+   _allocs_seen(0),
+   _mode(none) {
  
    reset_gc_id();
    create_and_start();
    _periodic_task.enroll();
    if (ShenandoahPacing) {

@@ -78,38 +86,43 @@
  
  void ShenandoahControlThread::run_service() {
    ShenandoahHeap* heap = ShenandoahHeap::heap();
  
    GCMode default_mode = concurrent_normal;
+   GenerationMode generation = GLOBAL;
    GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
-   int sleep = ShenandoahControlIntervalMin;
  
    double last_shrink_time = os::elapsedTime();
-   double last_sleep_adjust_time = os::elapsedTime();
+   uint age_period = 0;
  
    // Shrink period avoids constantly polling regions for shrinking.
    // Having a period 10x lower than the delay would mean we hit the
    // shrinking with lag of less than 1/10-th of true delay.
    // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
    double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
  
    ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
-   ShenandoahHeuristics* heuristics = heap->heuristics();
+ 
+   // Heuristics are notified of allocation failures here and other outcomes
+   // of the cycle. They're also used here to control whether the Nth consecutive
+   // degenerated cycle should be 'promoted' to a full cycle. The decision to
+   // trigger a cycle or not is evaluated on the regulator thread.
+   ShenandoahHeuristics* global_heuristics = heap->global_generation()->heuristics();
    while (!in_graceful_shutdown() && !should_terminate()) {
      // Figure out if we have pending requests.
      bool alloc_failure_pending = _alloc_failure_gc.is_set();
-     bool explicit_gc_requested = _gc_requested.is_set() &&  is_explicit_gc(_requested_gc_cause);
-     bool implicit_gc_requested = _gc_requested.is_set() && !is_explicit_gc(_requested_gc_cause);
+     bool explicit_gc_requested = _gc_requested.is_set() && is_explicit_gc(_requested_gc_cause);
+     bool implicit_gc_requested = _gc_requested.is_set() && is_implicit_gc(_requested_gc_cause);
  
      // This control loop iteration have seen this much allocations.
      size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0, memory_order_relaxed);
  
      // Check if we have seen a new target for soft max heap size.
      bool soft_max_changed = check_soft_max_changed();
  
      // Choose which GC mode to run in. The block below should select a single mode.
-     GCMode mode = none;
+     set_gc_mode(none);
      GCCause::Cause cause = GCCause::_last_gc_cause;
      ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
  
      if (alloc_failure_pending) {
        // Allocation failure takes precedence: we have to deal with it first thing

@@ -119,69 +132,105 @@
  
        // Consume the degen point, and seed it with default value
        degen_point = _degen_point;
        _degen_point = ShenandoahGC::_degenerated_outside_cycle;
  
-       if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle()) {
+       if (degen_point == ShenandoahGC::_degenerated_outside_cycle) {
+         _degen_generation = heap->mode()->is_generational() ? heap->young_generation() : heap->global_generation();
+       } else {
+         assert(_degen_generation != NULL, "Need to know which generation to resume.");
+       }
+ 
+       ShenandoahHeuristics* heuristics = _degen_generation->heuristics();
+       generation = _degen_generation->generation_mode();
+       bool old_gen_evacuation_failed = heap->clear_old_evacuation_failure();
+ 
+       // Do not bother with degenerated cycle if old generation evacuation failed.
+       if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle() && !old_gen_evacuation_failed) {
          heuristics->record_allocation_failure_gc();
          policy->record_alloc_failure_to_degenerated(degen_point);
-         mode = stw_degenerated;
+         set_gc_mode(stw_degenerated);
        } else {
          heuristics->record_allocation_failure_gc();
          policy->record_alloc_failure_to_full();
-         mode = stw_full;
+         generation = GLOBAL;
+         set_gc_mode(stw_full);
        }
- 
      } else if (explicit_gc_requested) {
+       generation = GLOBAL;
        cause = _requested_gc_cause;
        log_info(gc)("Trigger: Explicit GC request (%s)", GCCause::to_string(cause));
  
-       heuristics->record_requested_gc();
+       global_heuristics->record_requested_gc();
  
        if (ExplicitGCInvokesConcurrent) {
          policy->record_explicit_to_concurrent();
-         mode = default_mode;
+         set_gc_mode(default_mode);
          // Unload and clean up everything
-         heap->set_unload_classes(heuristics->can_unload_classes());
+         heap->set_unload_classes(global_heuristics->can_unload_classes());
        } else {
          policy->record_explicit_to_full();
-         mode = stw_full;
+         set_gc_mode(stw_full);
        }
      } else if (implicit_gc_requested) {
+       generation = GLOBAL;
        cause = _requested_gc_cause;
        log_info(gc)("Trigger: Implicit GC request (%s)", GCCause::to_string(cause));
  
-       heuristics->record_requested_gc();
+       global_heuristics->record_requested_gc();
  
        if (ShenandoahImplicitGCInvokesConcurrent) {
          policy->record_implicit_to_concurrent();
-         mode = default_mode;
+         set_gc_mode(default_mode);
  
          // Unload and clean up everything
-         heap->set_unload_classes(heuristics->can_unload_classes());
+         heap->set_unload_classes(global_heuristics->can_unload_classes());
        } else {
          policy->record_implicit_to_full();
-         mode = stw_full;
+         set_gc_mode(stw_full);
        }
      } else {
-       // Potential normal cycle: ask heuristics if it wants to act
-       if (heuristics->should_start_gc()) {
-         mode = default_mode;
-         cause = default_cause;
+       // We should only be here if the regulator requested a cycle or if
+       // there is an old generation mark in progress.
+       if (_requested_gc_cause == GCCause::_shenandoah_concurrent_gc) {
+         // preemption was requested or this is a regular cycle
+         cause = GCCause::_shenandoah_concurrent_gc;
+         generation = _requested_generation;
+         set_gc_mode(default_mode);
+ 
+         // Don't start a new old marking if there is one already in progress.
+         if (generation == OLD && heap->is_concurrent_old_mark_in_progress()) {
+           set_gc_mode(marking_old);
+         }
+ 
+         if (generation == GLOBAL) {
+           heap->set_unload_classes(global_heuristics->should_unload_classes());
+         } else {
+           heap->set_unload_classes(false);
+         }
+       } else if (heap->is_concurrent_old_mark_in_progress() || heap->is_concurrent_prep_for_mixed_evacuation_in_progress()) {
+         // Nobody asked us to do anything, but we have an old-generation mark or old-generation preparation for
+         // mixed evacuation in progress, so resume working on that.
+         cause = GCCause::_shenandoah_concurrent_gc;
+         generation = OLD;
+         set_gc_mode(marking_old);
        }
  
-       // Ask policy if this cycle wants to process references or unload classes
-       heap->set_unload_classes(heuristics->should_unload_classes());
+       // Don't want to spin in this loop and start a cycle every time, so
+       // clear requested gc cause. This creates a race with callers of the
+       // blocking 'request_gc' method, but there it loops and resets the
+       // '_requested_gc_cause' until a full cycle is completed.
+       _requested_gc_cause = GCCause::_no_gc;
      }
  
      // Blow all soft references on this cycle, if handling allocation failure,
-     // either implicit or explicit GC request,  or we are requested to do so unconditionally.
-     if (alloc_failure_pending || implicit_gc_requested || explicit_gc_requested || ShenandoahAlwaysClearSoftRefs) {
+     // either implicit or explicit GC request, or we are requested to do so unconditionally.
+     if (generation == GLOBAL && (alloc_failure_pending || implicit_gc_requested || explicit_gc_requested || ShenandoahAlwaysClearSoftRefs)) {
        heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
      }
  
-     bool gc_requested = (mode != none);
+     bool gc_requested = (_mode != none);
      assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
  
      if (gc_requested) {
        // GC is starting, bump the internal ID
        update_gc_id();

@@ -198,22 +247,41 @@
        {
          ShenandoahHeapLocker locker(heap->lock());
          heap->free_set()->log_status();
        }
  
-       switch (mode) {
-         case concurrent_normal:
-           service_concurrent_normal_cycle(cause);
-           break;
-         case stw_degenerated:
-           service_stw_degenerated_cycle(cause, degen_point);
-           break;
-         case stw_full:
-           service_stw_full_cycle(cause);
-           break;
-         default:
-           ShouldNotReachHere();
+       heap->set_aging_cycle(false);
+       {
+         switch (_mode) {
+           case concurrent_normal: {
+             if ((generation == YOUNG) && (age_period-- == 0)) {
+               heap->set_aging_cycle(true);
+               age_period = ShenandoahAgingCyclePeriod - 1;
+             }
+             service_concurrent_normal_cycle(heap, generation, cause);
+             break;
+           }
+           case stw_degenerated: {
+             if (!service_stw_degenerated_cycle(cause, degen_point)) {
+               // The degenerated GC was upgraded to a Full GC
+               generation = GLOBAL;
+             }
+             break;
+           }
+           case stw_full: {
+             service_stw_full_cycle(cause);
+             break;
+           }
+           case marking_old: {
+             assert(generation == OLD, "Expected old generation here");
+             resume_concurrent_old_cycle(heap->old_generation(), cause);
+             break;
+           }
+           default: {
+             ShouldNotReachHere();
+           }
+         }
        }
  
        // If this was the requested GC cycle, notify waiters about it
        if (explicit_gc_requested || implicit_gc_requested) {
          notify_gc_waiters();

@@ -247,11 +315,12 @@
        // Retract forceful part of soft refs policy
        heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
  
        // Clear metaspace oom flag, if current cycle unloaded classes
        if (heap->unload_classes()) {
-         heuristics->clear_metaspace_oom();
+         assert(generation == GLOBAL, "Only unload classes during GLOBAL cycle");
+         global_heuristics->clear_metaspace_oom();
        }
  
        // Commit worker statistics to cycle data
        heap->phase_timings()->flush_par_workers_to_cycle();
        if (ShenandoahPacing) {

@@ -306,28 +375,119 @@
        service_uncommit(shrink_before, shrink_until);
        heap->phase_timings()->flush_cycle_to_global();
        last_shrink_time = current;
      }
  
-     // Wait before performing the next action. If allocation happened during this wait,
-     // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
-     // back off exponentially.
-     if (_heap_changed.try_unset()) {
-       sleep = ShenandoahControlIntervalMin;
-     } else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
-       sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
-       last_sleep_adjust_time = current;
+     // Don't wait around if there was an allocation failure - start the next cycle immediately.
+     if (!is_alloc_failure_gc()) {
+       // The timed wait is necessary because this thread has a responsibility to send
+       // 'alloc_words' to the pacer when it does not perform a GC.
+       MonitorLocker lock(&_control_lock, Mutex::_no_safepoint_check_flag);
+       lock.wait(ShenandoahControlIntervalMax);
      }
-     os::naked_short_sleep(sleep);
    }
  
    // Wait for the actual stop(), can't leave run_service() earlier.
    while (!should_terminate()) {
      os::naked_short_sleep(ShenandoahControlIntervalMin);
    }
  }
  
+ // Young and old concurrent cycles are initiated by the regulator. Implicit
+ // and explicit GC requests are handled by the controller thread and always
+ // run a global cycle (which is concurrent by default, but may be overridden
+ // by command line options). Old cycles always degenerate to a global cycle.
+ // Young cycles are degenerated to complete the young cycle.  Young
+ // and old degen may upgrade to Full GC.  Full GC may also be
+ // triggered directly by a System.gc() invocation.
+ //
+ //
+ //      +-----+ Idle +-----+-----------+---------------------+
+ //      |         +        |           |                     |
+ //      |         |        |           |                     |
+ //      |         |        v           |                     |
+ //      |         |  Bootstrap Old +-- | ------------+       |
+ //      |         |   +                |             |       |
+ //      |         |   |                |             |       |
+ //      |         v   v                v             v       |
+ //      |    Resume Old <----------+ Young +--> Young Degen  |
+ //      |     +  +                                   +       |
+ //      v     |  |                                   |       |
+ //   Global <-+  |                                   |       |
+ //      +        |                                   |       |
+ //      |        v                                   v       |
+ //      +--->  Global Degen +--------------------> Full <----+
+ //
+ void ShenandoahControlThread::service_concurrent_normal_cycle(
+   const ShenandoahHeap* heap, const GenerationMode generation, GCCause::Cause cause) {
+ 
+   switch (generation) {
+     case YOUNG: {
+       // Run a young cycle. This might or might not, have interrupted an ongoing
+       // concurrent mark in the old generation. We need to think about promotions
+       // in this case. Promoted objects should be above the TAMS in the old regions
+       // they end up in, but we have to be sure we don't promote into any regions
+       // that are in the cset.
+       log_info(gc, ergo)("Start GC cycle (YOUNG)");
+       service_concurrent_cycle(heap->young_generation(), cause, false);
+       heap->young_generation()->log_status();
+       break;
+     }
+     case GLOBAL: {
+       log_info(gc, ergo)("Start GC cycle (GLOBAL)");
+       service_concurrent_cycle(heap->global_generation(), cause, false);
+       heap->global_generation()->log_status();
+       break;
+     }
+     case OLD: {
+       log_info(gc, ergo)("Start GC cycle (OLD)");
+       service_concurrent_old_cycle(heap, cause);
+       heap->old_generation()->log_status();
+       break;
+     }
+     default:
+       ShouldNotReachHere();
+   }
+ }
+ 
+ void ShenandoahControlThread::service_concurrent_old_cycle(const ShenandoahHeap* heap, GCCause::Cause &cause) {
+   // Configure the young generation's concurrent mark to put objects in
+   // old regions into the concurrent mark queues associated with the old
+   // generation. The young cycle will run as normal except that rather than
+   // ignore old references it will mark and enqueue them in the old concurrent
+   // mark but it will not traverse them.
+   ShenandoahGeneration* old_generation = heap->old_generation();
+   ShenandoahYoungGeneration* young_generation = heap->young_generation();
+ 
+   assert(!heap->is_concurrent_old_mark_in_progress(), "Old already in progress.");
+   assert(old_generation->task_queues()->is_empty(), "Old mark queues should be empty.");
+ 
+   young_generation->set_old_gen_task_queues(old_generation->task_queues());
+   young_generation->set_mark_incomplete();
+   old_generation->set_mark_incomplete();
+   service_concurrent_cycle(young_generation, cause, true);
+   if (!heap->cancelled_gc()) {
+     // Reset the degenerated point. Normally this would happen at the top
+     // of the control loop, but here we have just completed a young cycle
+     // which has bootstrapped the old concurrent marking.
+     _degen_point = ShenandoahGC::_degenerated_outside_cycle;
+ 
+     // TODO: Bit of a hack here to keep the phase timings happy as we transition
+     // to concurrent old marking. We need to revisit this.
+     heap->phase_timings()->flush_par_workers_to_cycle();
+     heap->phase_timings()->flush_cycle_to_global();
+ 
+     // From here we will 'resume' the old concurrent mark. This will skip reset
+     // and init mark for the concurrent mark. All of that work will have been
+     // done by the bootstrapping young cycle. In order to simplify the debugging
+     // effort, the old cycle will ONLY complete the mark phase. No actual
+     // collection of the old generation is happening here.
+     set_gc_mode(marking_old);
+     resume_concurrent_old_cycle(old_generation, cause);
+   }
+ }
+ 
  bool ShenandoahControlThread::check_soft_max_changed() const {
    ShenandoahHeap* heap = ShenandoahHeap::heap();
    size_t new_soft_max = Atomic::load(&SoftMaxHeapSize);
    size_t old_soft_max = heap->soft_max_capacity();
    if (new_soft_max != old_soft_max) {

@@ -343,11 +503,50 @@
      }
    }
    return false;
  }
  
- void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
+ void ShenandoahControlThread::resume_concurrent_old_cycle(ShenandoahGeneration* generation, GCCause::Cause cause) {
+ 
+   assert(ShenandoahHeap::heap()->is_concurrent_old_mark_in_progress() ||
+          ShenandoahHeap::heap()->is_concurrent_prep_for_mixed_evacuation_in_progress(),
+          "Old mark or mixed-evac prep should be in progress");
+   log_debug(gc)("Resuming old generation with " UINT32_FORMAT " marking tasks queued.", generation->task_queues()->tasks());
+ 
+   ShenandoahHeap* heap = ShenandoahHeap::heap();
+ 
+   GCIdMark gc_id_mark;
+   ShenandoahGCSession session(cause, generation);
+ 
+   TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
+   // We can only tolerate being cancelled during concurrent marking or during preparation for mixed
+   // evacuation. This flag here (passed by reference) is used to control precisely where the regulator
+   // is allowed to cancel a GC.
+   ShenandoahOldGC gc(generation, _allow_old_preemption);
+   if (gc.collect(cause)) {
+     // Old collection is complete, the young generation no longer needs this
+     // reference to the old concurrent mark so clean it up.
+     heap->young_generation()->set_old_gen_task_queues(NULL);
+     generation->heuristics()->record_success_concurrent();
+     heap->shenandoah_policy()->record_success_concurrent();
+   }
+ 
+   if (heap->cancelled_gc()) {
+     // It's possible the gc cycle was cancelled after the last time
+     // the collection checked for cancellation. In which case, the
+     // old gc cycle is still completed, and we have to deal with this
+     // cancellation. We set the degeneration point to be outside
+     // the cycle because if this is an allocation failure, that is
+     // what must be done (there is no degenerated old cycle). If the
+     // cancellation was due to a heuristic wanting to start a young
+     // cycle, then we are not actually going to a degenerated cycle,
+     // so the degenerated point doesn't matter here.
+     check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle);
+   }
+ }
+ 
+ void ShenandoahControlThread::service_concurrent_cycle(ShenandoahGeneration* generation, GCCause::Cause cause, bool do_old_gc_bootstrap) {
    // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
    // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
    // If second allocation failure happens during Degenerated GC cycle (for example, when GC
    // tries to evac something and no memory is available), cycle degrades to Full GC.
    //

@@ -383,67 +582,103 @@
    //
    ShenandoahHeap* heap = ShenandoahHeap::heap();
    if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
  
    GCIdMark gc_id_mark;
-   ShenandoahGCSession session(cause);
+   ShenandoahGCSession session(cause, generation);
  
    TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
  
-   ShenandoahConcurrentGC gc;
+   ShenandoahConcurrentGC gc(generation, do_old_gc_bootstrap);
    if (gc.collect(cause)) {
      // Cycle is complete
-     heap->heuristics()->record_success_concurrent();
+     generation->heuristics()->record_success_concurrent();
      heap->shenandoah_policy()->record_success_concurrent();
    } else {
      assert(heap->cancelled_gc(), "Must have been cancelled");
      check_cancellation_or_degen(gc.degen_point());
+     assert(generation->generation_mode() != OLD, "Old GC takes a different control path");
+     // Concurrent young-gen collection degenerates to young
+     // collection.  Same for global collections.
+     _degen_generation = generation;
    }
  }
  
  bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
    ShenandoahHeap* heap = ShenandoahHeap::heap();
-   if (heap->cancelled_gc()) {
-     assert (is_alloc_failure_gc() || in_graceful_shutdown(), "Cancel GC either for alloc failure GC, or gracefully exiting");
-     if (!in_graceful_shutdown()) {
-       assert (_degen_point == ShenandoahGC::_degenerated_outside_cycle,
-               "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
-       _degen_point = point;
-     }
+   if (!heap->cancelled_gc()) {
+     return false;
+   }
+ 
+   if (in_graceful_shutdown()) {
      return true;
    }
+ 
+   assert(_degen_point == ShenandoahGC::_degenerated_outside_cycle,
+          "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
+ 
+   if (is_alloc_failure_gc()) {
+     _degen_point = point;
+     return true;
+   }
+ 
+   if (_preemption_requested.is_set()) {
+     assert(_requested_generation == YOUNG, "Only young GCs may preempt old.");
+     _preemption_requested.unset();
+ 
+     // Old generation marking is only cancellable during concurrent marking.
+     // Once final mark is complete, the code does not check again for cancellation.
+     // If old generation was cancelled for an allocation failure, we wouldn't
+     // make it to this case. The calling code is responsible for forcing a
+     // cancellation due to allocation failure into a degenerated cycle.
+     _degen_point = point;
+     heap->clear_cancelled_gc(false /* clear oom handler */);
+     return true;
+   }
+ 
+   fatal("Cancel GC either for alloc failure GC, or gracefully exiting, or to pause old generation marking.");
    return false;
  }
  
  void ShenandoahControlThread::stop_service() {
    // Nothing to do here.
  }
  
  void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
+   ShenandoahHeap* const heap = ShenandoahHeap::heap();
+ 
    GCIdMark gc_id_mark;
-   ShenandoahGCSession session(cause);
+   ShenandoahGCSession session(cause, heap->global_generation());
  
    ShenandoahFullGC gc;
    gc.collect(cause);
  
-   ShenandoahHeap* const heap = ShenandoahHeap::heap();
-   heap->heuristics()->record_success_full();
+   heap->global_generation()->heuristics()->record_success_full();
    heap->shenandoah_policy()->record_success_full();
  }
  
- void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
+ bool ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
    assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
+   ShenandoahHeap* const heap = ShenandoahHeap::heap();
  
    GCIdMark gc_id_mark;
-   ShenandoahGCSession session(cause);
+   ShenandoahGCSession session(cause, _degen_generation);
+ 
+   ShenandoahDegenGC gc(point, _degen_generation);
+ 
+   // Just in case degenerated cycle preempted old-gen marking, clear the old-gen task queues.
+   heap->young_generation()->set_old_gen_task_queues(NULL);
  
-   ShenandoahDegenGC gc(point);
    gc.collect(cause);
  
-   ShenandoahHeap* const heap = ShenandoahHeap::heap();
-   heap->heuristics()->record_success_degenerated();
+   assert(heap->young_generation()->task_queues()->is_empty(), "Unexpected young generation marking tasks");
+   assert(heap->old_generation()->task_queues()->is_empty(), "Unexpected old generation marking tasks");
+   assert(heap->global_generation()->task_queues()->is_empty(), "Unexpected global generation marking tasks");
+ 
+   _degen_generation->heuristics()->record_success_degenerated();
    heap->shenandoah_policy()->record_success_degenerated();
+   return !gc.upgraded_to_full();
  }
  
  void ShenandoahControlThread::service_uncommit(double shrink_before, size_t shrink_until) {
    ShenandoahHeap* heap = ShenandoahHeap::heap();
  

@@ -470,10 +705,14 @@
  bool ShenandoahControlThread::is_explicit_gc(GCCause::Cause cause) const {
    return GCCause::is_user_requested_gc(cause) ||
           GCCause::is_serviceability_requested_gc(cause);
  }
  
+ bool ShenandoahControlThread::is_implicit_gc(GCCause::Cause cause) const {
+   return !is_explicit_gc(cause) && cause != GCCause::_shenandoah_concurrent_gc;
+ }
+ 
  void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
    assert(GCCause::is_user_requested_gc(cause) ||
           GCCause::is_serviceability_requested_gc(cause) ||
           cause == GCCause::_metadata_GC_clear_soft_refs ||
           cause == GCCause::_full_gc_alot ||

@@ -489,10 +728,45 @@
    } else {
      handle_requested_gc(cause);
    }
  }
  
+ bool ShenandoahControlThread::request_concurrent_gc(GenerationMode generation) {
+   if (_preemption_requested.is_set() || _gc_requested.is_set() || ShenandoahHeap::heap()->cancelled_gc()) {
+     // ignore subsequent requests from the heuristics
+     return false;
+   }
+ 
+   if (_mode == none) {
+     _requested_gc_cause = GCCause::_shenandoah_concurrent_gc;
+     _requested_generation = generation;
+     notify_control_thread();
+     return true;
+   }
+ 
+   if (preempt_old_marking(generation)) {
+     log_info(gc)("Preempting old generation mark to allow young GC.");
+     _requested_gc_cause = GCCause::_shenandoah_concurrent_gc;
+     _requested_generation = generation;
+     _preemption_requested.set();
+     ShenandoahHeap::heap()->cancel_gc(GCCause::_shenandoah_concurrent_gc);
+     notify_control_thread();
+     return true;
+   }
+ 
+   return false;
+ }
+ 
+ void ShenandoahControlThread::notify_control_thread() {
+   MonitorLocker locker(&_control_lock, Mutex::_no_safepoint_check_flag);
+   _control_lock.notify();
+ }
+ 
+ bool ShenandoahControlThread::preempt_old_marking(GenerationMode generation) {
+   return generation == YOUNG && _allow_old_preemption.try_unset();
+ }
+ 
  void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
    // Make sure we have at least one complete GC cycle before unblocking
    // from the explicit GC request.
    //
    // This is especially important for weak references cleanup and/or native

@@ -505,11 +779,11 @@
    size_t current_gc_id = get_gc_id();
    size_t required_gc_id = current_gc_id + 1;
    while (current_gc_id < required_gc_id) {
      _gc_requested.set();
      _requested_gc_cause = cause;
- 
+     notify_control_thread();
      if (cause != GCCause::_wb_breakpoint) {
        ml.wait();
      }
      current_gc_id = get_gc_id();
    }

@@ -589,14 +863,10 @@
    // Update monitoring counters when we took a new region. This amortizes the
    // update costs on slow path.
    if (_do_counters_update.is_unset()) {
      _do_counters_update.set();
    }
-   // Notify that something had changed.
-   if (_heap_changed.is_unset()) {
-     _heap_changed.set();
-   }
  }
  
  void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
    assert(ShenandoahPacing, "should only call when pacing is enabled");
    Atomic::add(&_allocs_seen, words, memory_order_relaxed);

@@ -637,5 +907,23 @@
  }
  
  bool ShenandoahControlThread::in_graceful_shutdown() {
    return _graceful_shutdown.is_set();
  }
+ 
+ const char* ShenandoahControlThread::gc_mode_name(ShenandoahControlThread::GCMode mode) {
+   switch (mode) {
+     case none:              return "idle";
+     case concurrent_normal: return "normal";
+     case stw_degenerated:   return "degenerated";
+     case stw_full:          return "full";
+     case marking_old:       return "old mark";
+     default:                return "unknown";
+   }
+ }
+ 
+ void ShenandoahControlThread::set_gc_mode(ShenandoahControlThread::GCMode new_mode) {
+   if (_mode != new_mode) {
+     log_info(gc)("Transition from: %s to: %s", gc_mode_name(_mode), gc_mode_name(new_mode));
+     _mode = new_mode;
+   }
+ }
< prev index next >