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 * Copyright (c) 2013, 2021, Red Hat, Inc. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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#ifndef SHARE_GC_SHENANDOAH_SHENANDOAHCOLLECTORPOLICY_HPP
#define SHARE_GC_SHENANDOAH_SHENANDOAHCOLLECTORPOLICY_HPP

#include "gc/shared/gcTrace.hpp"
#include "gc/shenandoah/shenandoahGC.hpp"
#include "gc/shenandoah/shenandoahSharedVariables.hpp"
#include "gc/shenandoah/shenandoahTrace.hpp"
#include "memory/allocation.hpp"
#include "utilities/ostream.hpp"

class ShenandoahCollectorPolicy : public CHeapObj<mtGC> {
private:
  size_t _success_concurrent_gcs;
  size_t _abbreviated_concurrent_gcs;
  size_t _success_degenerated_gcs;
  size_t _abbreviated_degenerated_gcs;
  // Written by control thread, read by mutators
  volatile size_t _success_full_gcs;
  uint _consecutive_degenerated_gcs;
  uint _consecutive_degenerated_gcs_without_progress;
  volatile size_t _consecutive_young_gcs;
  size_t _mixed_gcs;
  size_t _success_old_gcs;
  size_t _interrupted_old_gcs;
  size_t _alloc_failure_degenerated;
  size_t _alloc_failure_degenerated_upgrade_to_full;
  size_t _alloc_failure_full;
  size_t _collection_cause_counts[GCCause::_last_gc_cause];
  size_t _degen_point_counts[ShenandoahGC::_DEGENERATED_LIMIT];

  ShenandoahSharedFlag _in_shutdown;
  ShenandoahTracer* _tracer;

  void reset_consecutive_degenerated_gcs() {
    _consecutive_degenerated_gcs = 0;
    _consecutive_degenerated_gcs_without_progress = 0;
  }

public:
  // The most common scenario for lack of good progress following a degenerated GC is an accumulation of floating
  // garbage during the most recently aborted concurrent GC effort.  With generational GC, it is far more effective to
  // reclaim this floating garbage with another degenerated cycle (which focuses on young generation and might require
  // a pause of 200 ms) rather than a full GC cycle (which may require over 2 seconds with a 10 GB old generation).
  //
  // In generational mode, we'll only upgrade to full GC if we've done two degen cycles in a row and both indicated
  // bad progress.  In non-generational mode, we'll preserve the original behavior, which is to upgrade to full
  // immediately following a degenerated cycle with bad progress.  This preserves original behavior of non-generational
  // Shenandoah to avoid introducing "surprising new behavior."  It also makes less sense with non-generational
  // Shenandoah to replace a full GC with a degenerated GC, because both have similar pause times in non-generational
  // mode.
  static constexpr size_t GENERATIONAL_CONSECUTIVE_BAD_DEGEN_PROGRESS_THRESHOLD = 2;

  ShenandoahCollectorPolicy();

  void record_mixed_cycle();
  void record_success_old();
  void record_interrupted_old();

  // A collection cycle may be "abbreviated" if Shenandoah finds a sufficient percentage
  // of regions that contain no live objects (ShenandoahImmediateThreshold). These cycles
  // end after final mark, skipping the evacuation and reference-updating phases. Such
  // cycles are very efficient and are worth tracking. Note that both degenerated and
  // concurrent cycles can be abbreviated.
  void record_success_concurrent(bool is_young, bool is_abbreviated);

  // Record that a degenerated cycle has been completed. Note that such a cycle may or
  // may not make "progress". We separately track the total number of degenerated cycles,
  // the number of consecutive degenerated cycles and the number of consecutive cycles that
  // fail to make good progress.
  void record_degenerated(bool is_young, bool is_abbreviated, bool progress);
  void record_success_full();
  void record_alloc_failure_to_degenerated(ShenandoahGC::ShenandoahDegenPoint point);
  void record_alloc_failure_to_full();
  void record_degenerated_upgrade_to_full();
  void record_collection_cause(GCCause::Cause cause);

  void record_shutdown();
  bool is_at_shutdown() const;

  ShenandoahTracer* tracer() const {return _tracer;}

  void print_gc_stats(outputStream* out) const;

  size_t full_gc_count() const {
    return _success_full_gcs + _alloc_failure_degenerated_upgrade_to_full;
  }

  // If the heuristics find that the number of consecutive degenerated cycles is above
  // ShenandoahFullGCThreshold, then they will initiate a Full GC upon an allocation
  // failure.
  size_t consecutive_degenerated_gc_count() const {
    return _consecutive_degenerated_gcs;
  }

  // Genshen will only upgrade to a full gc after the configured number of futile degenerated cycles.
  bool generational_should_upgrade_degenerated_gc() const {
    return _consecutive_degenerated_gcs_without_progress >= GENERATIONAL_CONSECUTIVE_BAD_DEGEN_PROGRESS_THRESHOLD;
  }

  static bool is_allocation_failure(GCCause::Cause cause);
  static bool is_shenandoah_gc(GCCause::Cause cause);
  static bool is_requested_gc(GCCause::Cause cause);
  static bool is_explicit_gc(GCCause::Cause cause);
  static bool should_run_full_gc(GCCause::Cause cause);
  static bool should_handle_requested_gc(GCCause::Cause cause);

  size_t consecutive_young_gc_count() const {
    return _consecutive_young_gcs;
  }

private:
  void update_young(bool is_young);
};

#endif // SHARE_GC_SHENANDOAH_SHENANDOAHCOLLECTORPOLICY_HPP