/*

 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

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

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * 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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 */

#ifndef SHARE_VM_RUNTIME_SWEEPER_HPP

#define SHARE_VM_RUNTIME_SWEEPER_HPP

#include "utilities/ticks.hpp"

// An NmethodSweeper is an incremental cleaner for:

//    - cleanup inline caches

//    - reclamation of nmethods

// Removing nmethods from the code cache includes two operations

//  1) mark active nmethods

//     Is done in 'mark_active_nmethods()'. This function is called at a

//     safepoint and marks all nmethods that are active on a thread's stack.

//  2) sweep nmethods

//     Is done in sweep_code_cache(). This function is the only place in the

//     sweeper where memory is reclaimed. Note that sweep_code_cache() is not

//     called at a safepoint. However, sweep_code_cache() stops executing if

//     another thread requests a safepoint. Consequently, 'mark_active_nmethods()'

//     and sweep_code_cache() cannot execute at the same time.

//     To reclaim memory, nmethods are first marked as 'not-entrant'. Methods can

//     be made not-entrant by (i) the sweeper, (ii) deoptimization, (iii) dependency

//     invalidation, and (iv) being replaced be a different method version (tiered

//     compilation). Not-entrant nmethod cannot be called by Java threads, but they

//     can still be active on the stack. To ensure that active nmethod are not reclaimed,

//     we have to wait until the next marking phase has completed. If a not-entrant

//     nmethod was NOT marked as active, it can be converted to 'zombie' state. To safely

//     remove the nmethod, all inline caches (IC) that point to the the nmethod must be

//     cleared. After that, the nmethod can be evicted from the code cache. Each nmethod's

//     state change happens during separate sweeps. It may take at least 3 sweeps before an

//     nmethod's space is freed. Sweeping is currently done by compiler threads between

//     compilations or at least each 5 sec (NmethodSweepCheckInterval) when the code cache

//     is full.

class NMethodSweeper : public AllStatic {

  // Stat counters

  static int  process_nmethod(nmethod *nm);

  static void release_nmethod(nmethod* nm);

  static bool sweep_in_progress();

  static void sweep_code_cache();

 public:

  static long traversal_count()              { return _traversals; }

  static int  total_nof_methods_reclaimed()  { return _total_nof_methods_reclaimed; }

  static const Tickspan total_time_sweeping()      { return _total_time_sweeping; }

  static const Tickspan peak_sweep_time()          { return _peak_sweep_time; }

  static const Tickspan peak_sweep_fraction_time() { return _peak_sweep_fraction_time; }

  static void log_sweep(const char* msg, const char* format = NULL, ...);

#ifdef ASSERT

  static bool is_sweeping(nmethod* which) { return _current == which; }

  // Keep track of sweeper activity in the ring buffer

  static void record_sweep(nmethod* nm, int line);

  static void report_events(int id, address entry);

  static void report_events();

#endif

  static void mark_active_nmethods();      // Invoked at the end of each safepoint

  static void possibly_sweep();            // Compiler threads call this to sweep

  static int hotness_counter_reset_val();

  static void report_state_change(nmethod* nm);

  static void possibly_enable_sweeper();

};

#endif // SHARE_VM_RUNTIME_SWEEPER_HPP