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 *

 * This code is free software; you can redistribute it and/or modify it

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 * published by the Free Software Foundation.

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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * 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).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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//

// 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/shared/stringdedup/stringDedup.hpp"

#include "memory/allocation.hpp"

#include "oops/oop.hpp"

class OopClosure;

class BoolObjectClosure;

class G1GCPhaseTimes;

class G1StringDedupUnlinkOrOopsDoClosure;

//

// G1 interface for interacting with string deduplication.

//

class G1StringDedup : public StringDedup {

private:

  // Candidate selection policies, returns true if the given object is

  // candidate for string deduplication.

  static bool is_candidate_from_mark(oop obj);

  static bool is_candidate_from_evacuation(bool from_young, bool to_young, oop obj);

public:

  // Initialize string deduplication.

  static void initialize();

  // Enqueues a deduplication candidate for later processing by the deduplication

  // thread. Before enqueuing, these functions apply the appropriate candidate

  // selection policy to filters out non-candidates.

  static void enqueue_from_mark(oop java_string, uint worker_id);

  static void enqueue_from_evacuation(bool from_young, bool to_young,

                                      unsigned int queue, oop java_string);

  static void oops_do(OopClosure* keep_alive);

  static void parallel_unlink(G1StringDedupUnlinkOrOopsDoClosure* unlink, uint worker_id);

  static void unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* keep_alive,

                                bool allow_resize_and_rehash, G1GCPhaseTimes* phase_times = NULL);

};

//

// This closure encapsulates the state and the closures needed when scanning

// the deduplication queue and table during the unlink_or_oops_do() operation.

// A single instance of this closure is created and then shared by all worker

// threads participating in the scan.

//

class G1StringDedupUnlinkOrOopsDoClosure : public StringDedupUnlinkOrOopsDoClosure {

public:

  G1StringDedupUnlinkOrOopsDoClosure(BoolObjectClosure* is_alive,

                                     OopClosure* keep_alive,

                                     bool allow_resize_and_rehash) :

    StringDedupUnlinkOrOopsDoClosure(is_alive, keep_alive) {

      if (G1StringDedup::is_enabled()) {

        G1StringDedup::gc_prologue(allow_resize_and_rehash);

      }

    }

  ~G1StringDedupUnlinkOrOopsDoClosure() {

    if (G1StringDedup::is_enabled()) {

      G1StringDedup::gc_epilogue();

    }

  }

};