1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  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).
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  24 
  25 #ifndef SHARE_VM_RUNTIME_SWEEPER_HPP
  26 #define SHARE_VM_RUNTIME_SWEEPER_HPP
  27 
  28 // An NmethodSweeper is an incremental cleaner for:
  29 //    - cleanup inline caches
  30 //    - reclamation of nmethods
  31 // Removing nmethods from the code cache includes two operations
  32 //  1) mark active nmethods
  33 //     Is done in 'mark_active_nmethods()'. This function is called at a
  34 //     safepoint and marks all nmethods that are active on a thread's stack.
  35 //  2) sweep nmethods
  36 //     Is done in sweep_code_cache(). This function is the only place in the
  37 //     sweeper where memory is reclaimed. Note that sweep_code_cache() is not
  38 //     called at a safepoint. However, sweep_code_cache() stops executing if
  39 //     another thread requests a safepoint. Consequently, 'mark_active_nmethods()'
  40 //     and sweep_code_cache() cannot execute at the same time.
  41 //     To reclaim memory, nmethods are first marked as 'not-entrant'. Methods can
  42 //     be made not-entrant by (i) the sweeper, (ii) deoptimization, (iii) dependency
  43 //     invalidation, and (iv) being replaced be a different method version (tiered
  44 //     compilation). Not-entrant nmethod cannot be called by Java threads, but they
  45 //     can still be active on the stack. To ensure that active nmethod are not reclaimed,
  46 //     we have to wait until the next marking phase has completed. If a not-entrant
  47 //     nmethod was NOT marked as active, it can be converted to 'zombie' state. To safely
  48 //     remove the nmethod, all inline caches (IC) that point to the the nmethod must be
  49 //     cleared. After that, the nmethod can be evicted from the code cache. Each nmethod's
  50 //     state change happens during separate sweeps. It may take at least 3 sweeps before an
  51 //     nmethod's space is freed. Sweeping is currently done by compiler threads between
  52 //     compilations or at least each 5 sec (NmethodSweepCheckInterval) when the code cache
  53 //     is full.
  54 
  55 class NMethodSweeper : public AllStatic {
  56   static long      _traversals;      // Stack scan count, also sweep ID.
  57   static nmethod*  _current;         // Current nmethod
  58   static int       _seen;            // Nof. nmethod we have currently processed in current pass of CodeCache
  59   static int       _flushed_count;   // Nof. nmethods flushed in current sweep
  60   static int       _zombified_count; // Nof. nmethods made zombie in current sweep
  61   static int       _marked_count;    // Nof. nmethods marked for reclaim in current sweep
  62 
  63   static volatile int  _invocations;   // No. of invocations left until we are completed with this pass
  64   static volatile int  _sweep_started; // Flag to control conc sweeper
  65 
  66   //The following are reset in mark_active_nmethods and synchronized by the safepoint
  67   static bool      _request_mark_phase;        // Indicates that a change has happend and we need another mark pahse,
  68                                                // always checked and reset at a safepoint so memory will be in sync.
  69   static int       _locked_seen;               // Number of locked nmethods encountered during the scan
  70   static int       _not_entrant_seen_on_stack; // Number of not entrant nmethod were are still on stack









  71 
  72   // Stat counters

  73   static int       _total_nof_methods_reclaimed;  // Accumulated nof methods flushed
  74   static jlong     _total_time_sweeping;          // Accumulated time sweeping
  75   static jlong     _total_time_this_sweep;        // Total time this sweep
  76   static jlong     _peak_sweep_time;              // Peak time for a full sweep
  77   static jlong     _peak_sweep_fraction_time;     // Peak time sweeping one fraction


  78 
  79   static int  process_nmethod(nmethod *nm);
  80   static void release_nmethod(nmethod* nm);
  81 

  82   static bool sweep_in_progress();
  83   static void sweep_code_cache();
  84   static void request_nmethod_marking() { _request_mark_phase = true; }
  85   static void reset_nmethod_marking()   { _request_mark_phase = false; }
  86   static bool need_marking_phase()      { return _request_mark_phase; }
  87 
  88   static int _hotness_counter_reset_val;
  89 
  90  public:
  91   static long traversal_count()              { return _traversals; }

  92   static int  total_nof_methods_reclaimed()  { return _total_nof_methods_reclaimed; }
  93   static jlong total_time_sweeping()         { return _total_time_sweeping; }
  94   static jlong peak_sweep_time()             { return _peak_sweep_time; }
  95   static jlong peak_sweep_fraction_time()    { return _peak_sweep_fraction_time; }
  96   static void log_sweep(const char* msg, const char* format = NULL, ...);
  97 
  98 
  99 #ifdef ASSERT
 100   static bool is_sweeping(nmethod* which) { return _current == which; }
 101   // Keep track of sweeper activity in the ring buffer
 102   static void record_sweep(nmethod* nm, int line);
 103   static void report_events(int id, address entry);
 104   static void report_events();
 105 #endif
 106 
 107   static void mark_active_nmethods();      // Invoked at the end of each safepoint

 108   static void possibly_sweep();            // Compiler threads call this to sweep
 109 
 110   static int sort_nmethods_by_hotness(nmethod** nm1, nmethod** nm2);
 111   static int hotness_counter_reset_val();
 112 
 113   static void notify() {
 114     // Request a new sweep of the code cache from the beginning. No
 115     // need to synchronize the setting of this flag since it only
 116     // changes to false at safepoint so we can never overwrite it with false.
 117      request_nmethod_marking();
 118   }



 119 };
 120 
 121 #endif // SHARE_VM_RUNTIME_SWEEPER_HPP
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