src/hotspot/share/gc/g1/g1StringDedup.hpp

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#ifndef SHARE_GC_G1_G1STRINGDEDUP_HPP
#define SHARE_GC_G1_G1STRINGDEDUP_HPP

//
// G1 string deduplication candidate selection
//
// An object is considered a deduplication candidate if all of the following
// statements are true:
//
// - The object is an instance of java.lang.String
//
// - The object is being evacuated from a young heap region
//
// - The object is being evacuated to a young/survivor heap region and the
//   object's age is equal to the deduplication age threshold
//
//   or
//
//   The object is being evacuated to an old heap region and the object's age is
//   less than the deduplication age threshold
//
// Once an string object has been promoted to an old region, or its age is higher
// than the deduplication age threshold, is will never become a candidate again.
// This approach avoids making the same object a candidate more than once.
//

#include "gc/g1/g1HeapRegionAttr.hpp"
#include "gc/shared/stringdedup/stringDedup.hpp"
#include "memory/allStatic.hpp"
#include "oops/oopsHierarchy.hpp"

class G1StringDedup : AllStatic {
public:
  // Candidate selection policy for full GC, returning true if the given
  // String is a candidate for string deduplication.
  // precondition: StringDedup::is_enabled()
  // precondition: java_string is a Java String
  static bool is_candidate_from_mark(oop java_string);

  // Candidate selection policy for young/mixed GC.
  // If to is young then age should be the new (survivor's) age.
  // if to is old then age should be the age of the copied from object.
  static bool is_candidate_from_evacuation(const Klass* klass,
                                           G1HeapRegionAttr from,
                                           G1HeapRegionAttr to,
                                           uint age) {
    return StringDedup::is_enabled_string(klass) &&
           from.is_young() &&
           (to.is_young() ?
            StringDedup::is_threshold_age(age) :
            StringDedup::is_below_threshold_age(age));
  }
};

#endif // SHARE_GC_G1_G1STRINGDEDUP_HPP