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 /*

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

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

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  * 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

 // 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 {

   static long      _traversals;                   // Stack scan count, also sweep ID.

   static long      _time_counter;                 // Virtual time used to periodically invoke sweeper

   static long      _last_sweep;                   // Value of _time_counter when the last sweep happened

   static nmethod*  _current;                      // Current nmethod

   static int       _seen;                         // Nof. nmethod we have currently processed in current pass of CodeCache

   static int       _flushed_count;                // Nof. nmethods flushed in current sweep

   static int       _zombified_count;              // Nof. nmethods made zombie in current sweep

   static int       _marked_for_reclamation_count; // Nof. nmethods marked for reclaim in current sweep

   static volatile int  _sweep_fractions_left;     // Nof. invocations left until we are completed with this pass

   static volatile int  _sweep_started;            // Flag to control conc sweeper

   static volatile bool _should_sweep;             // Indicates if we should invoke the sweeper

   static volatile int _bytes_changed;             // Counts the total nmethod size if the nmethod changed from:

                                                   //   1) alive       -> not_entrant

                                                   //   2) not_entrant -> zombie

                                                   //   3) zombie      -> marked_for_reclamation

   // Stat counters

   static int       _total_nof_methods_reclaimed;  // Accumulated nof methods flushed

   static jlong     _total_time_sweeping;          // Accumulated time sweeping

   static jlong     _total_time_this_sweep;        // Total time this sweep

   static jlong     _peak_sweep_time;              // Peak time for a full sweep

   static jlong     _peak_sweep_fraction_time;     // Peak time sweeping one fraction

   static int  process_nmethod(nmethod *nm);

   static void release_nmethod(nmethod* nm);

   static bool sweep_in_progress();

   static void sweep_code_cache();

   static int _hotness_counter_reset_val;

  public:

   static long traversal_count()              { return _traversals; }

   static int  total_nof_methods_reclaimed()  { return _total_nof_methods_reclaimed; }

   static jlong total_time_sweeping()         { return _total_time_sweeping; }

   static jlong peak_sweep_time()             { return _peak_sweep_time; }

   static jlong 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 sort_nmethods_by_hotness(nmethod** nm1, nmethod** nm2);

   static int hotness_counter_reset_val();

   static void report_state_change(nmethod* nm);

   static void possibly_enable_sweeper();

 };

 #endif // SHARE_VM_RUNTIME_SWEEPER_HPP