1 /*
   2  * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
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   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_VM_RUNTIME_SWEEPER_HPP
  26 #define SHARE_VM_RUNTIME_SWEEPER_HPP
  27 
  28 class WhiteBox;
  29 
  30 #include "utilities/ticks.hpp"
  31 // An NmethodSweeper is an incremental cleaner for:
  32 //    - cleanup inline caches
  33 //    - reclamation of nmethods
  34 // Removing nmethods from the code cache includes two operations
  35 //  1) mark active nmethods
  36 //     Is done in 'mark_active_nmethods()'. This function is called at a
  37 //     safepoint and marks all nmethods that are active on a thread's stack.
  38 //  2) sweep nmethods
  39 //     Is done in sweep_code_cache(). This function is the only place in the
  40 //     sweeper where memory is reclaimed. Note that sweep_code_cache() is not
  41 //     called at a safepoint. However, sweep_code_cache() stops executing if
  42 //     another thread requests a safepoint. Consequently, 'mark_active_nmethods()'
  43 //     and sweep_code_cache() cannot execute at the same time.
  44 //     To reclaim memory, nmethods are first marked as 'not-entrant'. Methods can
  45 //     be made not-entrant by (i) the sweeper, (ii) deoptimization, (iii) dependency
  46 //     invalidation, and (iv) being replaced be a different method version (tiered
  47 //     compilation). Not-entrant nmethod cannot be called by Java threads, but they
  48 //     can still be active on the stack. To ensure that active nmethod are not reclaimed,
  49 //     we have to wait until the next marking phase has completed. If a not-entrant
  50 //     nmethod was NOT marked as active, it can be converted to 'zombie' state. To safely
  51 //     remove the nmethod, all inline caches (IC) that point to the the nmethod must be
  52 //     cleared. After that, the nmethod can be evicted from the code cache. Each nmethod's
  53 //     state change happens during separate sweeps. It may take at least 3 sweeps before an
  54 //     nmethod's space is freed.
  55 
  56 class NMethodSweeper : public AllStatic {
  57   friend class WhiteBox;
  58  private:
  59   enum MethodStateChange {
  60     None,
  61     MadeZombie,
  62     MarkedForReclamation,
  63     Flushed
  64   };
  65   static long      _traversals;                   // Stack scan count, also sweep ID.
  66   static long      _total_nof_code_cache_sweeps;  // Total number of full sweeps of the code cache
  67   static long      _time_counter;                 // Virtual time used to periodically invoke sweeper
  68   static long      _last_sweep;                   // Value of _time_counter when the last sweep happened
  69   static NMethodIterator _current;                // Current nmethod
  70   static int       _seen;                         // Nof. nmethod we have currently processed in current pass of CodeCache
  71 
  72   static volatile int  _sweep_started;            // Flag to control conc sweeper
  73   static volatile bool _should_sweep;             // Indicates if we should invoke the sweeper

  74   static volatile int _bytes_changed;             // Counts the total nmethod size if the nmethod changed from:
  75                                                   //   1) alive       -> not_entrant
  76                                                   //   2) not_entrant -> zombie
  77                                                   //   3) zombie      -> marked_for_reclamation
  78   // Stat counters
  79   static long      _total_nof_methods_reclaimed;    // Accumulated nof methods flushed
  80   static long      _total_nof_c2_methods_reclaimed; // Accumulated nof C2-compiled methods flushed
  81   static size_t    _total_flushed_size;             // Total size of flushed methods
  82   static int       _hotness_counter_reset_val;
  83 
  84   static Tickspan  _total_time_sweeping;          // Accumulated time sweeping
  85   static Tickspan  _total_time_this_sweep;        // Total time this sweep
  86   static Tickspan  _peak_sweep_time;              // Peak time for a full sweep
  87   static Tickspan  _peak_sweep_fraction_time;     // Peak time sweeping one fraction
  88 
  89   static Monitor*  _stat_lock;
  90 
  91   static MethodStateChange process_nmethod(nmethod *nm);
  92   static void              release_nmethod(nmethod* nm);
  93 
  94   static void init_sweeper_log() NOT_DEBUG_RETURN;
  95   static bool wait_for_stack_scanning();
  96   static void sweep_code_cache();
  97   static void handle_safepoint_request();
  98   static void do_stack_scanning();
  99   static void possibly_sweep();
 100  public:
 101   static long traversal_count()              { return _traversals; }
 102   static int  total_nof_methods_reclaimed()  { return _total_nof_methods_reclaimed; }
 103   static const Tickspan total_time_sweeping()      { return _total_time_sweeping; }
 104   static const Tickspan peak_sweep_time()          { return _peak_sweep_time; }
 105   static const Tickspan peak_sweep_fraction_time() { return _peak_sweep_fraction_time; }
 106   static void log_sweep(const char* msg, const char* format = NULL, ...) ATTRIBUTE_PRINTF(2, 3);
 107 
 108 
 109 #ifdef ASSERT
 110   static bool is_sweeping(nmethod* which) { return _current.method() == which; }
 111   // Keep track of sweeper activity in the ring buffer
 112   static void record_sweep(nmethod* nm, int line);
 113   static void report_events(int id, address entry);
 114   static void report_events();
 115 #endif
 116 
 117   static void mark_active_nmethods();      // Invoked at the end of each safepoint
 118   static void sweeper_loop();
 119   static void notify(int code_blob_type);  // Possibly start the sweeper thread.

 120 
 121   static int hotness_counter_reset_val();
 122   static void report_state_change(nmethod* nm);
 123   static void possibly_enable_sweeper();
 124   static void possibly_flush(nmethod* nm);
 125   static void print();   // Printing/debugging
 126 };
 127 
 128 #endif // SHARE_VM_RUNTIME_SWEEPER_HPP
--- EOF ---