src/hotspot/share/gc/shenandoah/shenandoahUncommitThread.hpp

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#ifndef SHARE_GC_SHENANDOAH_SHENANDOAHUNCOMMITTHREAD
#define SHARE_GC_SHENANDOAH_SHENANDOAHUNCOMMITTHREAD

#include "gc/shared/concurrentGCThread.hpp"

class ShenandoahHeap;

class ShenandoahUncommitThread : public ConcurrentGCThread {
  ShenandoahHeap* const _heap;

  // Indicates that `SoftMaxHeapSize` has changed
  ShenandoahSharedFlag _soft_max_changed;

  // Indicates that an explicit gc has been requested
  ShenandoahSharedFlag _explicit_gc_requested;

  // Indicates whether it is safe to uncommit regions
  ShenandoahSharedFlag _uncommit_allowed;

  // Indicates that regions are being actively uncommitted
  ShenandoahSharedFlag _uncommit_in_progress;

  // This lock is used to coordinate allowing or forbidding regions to be uncommitted
  Monitor _uncommit_lock;

  // True if there are regions to uncommit and uncommits are allowed
  bool should_uncommit(double shrink_before, size_t shrink_until) const;

  // True if there are regions that have been empty for longer than ShenandoahUncommitDelay and the committed
  // memory is higher than soft max capacity or minimum capacity
  bool has_work(double shrink_before, size_t shrink_until) const;

  // Perform the work of uncommitting empty regions
  void uncommit(double shrink_before, size_t shrink_until);

  // True if the control thread has allowed this thread to uncommit regions
  bool is_uncommit_allowed() const;

  // Iterate over and uncommit eligible regions until committed heap falls below
  // `shrink_until` bytes. A region is eligible for uncommit if the timestamp at which
  // it was last made empty is before `shrink_before` seconds since jvm start.
  // Returns the number of regions uncommitted. May be interrupted by `forbid_uncommit`.
  size_t do_uncommit_work(double shrink_before, size_t shrink_until) const;

public:
  explicit ShenandoahUncommitThread(ShenandoahHeap* heap);

  // Periodically check for regions to uncommit
  void run_service() override;

  // Wake up this thread and try to uncommit for changed soft max size
  void notify_soft_max_changed();

  // Wake up this thread and try to uncommit for min heap size
  void notify_explicit_gc_requested();

  // Wait for uncommit operations to stop, returns immediately if uncommit thread is idle
  void forbid_uncommit();

  // Allows uncommit operations to happen, does not block
  void allow_uncommit();

  // True if uncommit is in progress
  bool is_uncommit_in_progress() const {
    return _uncommit_in_progress.is_set();
  }
protected:
  // Interrupt and stop this thread
  void stop_service() override;
};


#endif //SHARE_GC_SHENANDOAH_SHENANDOAHUNCOMMITTHREAD