28 class WhiteBox;
  29 
  30 #include "code/codeCache.hpp"
  31 #include "utilities/ticks.hpp"
  32 
  33 // An NmethodSweeper is an incremental cleaner for:
  34 //    - cleanup inline caches
  35 //    - reclamation of nmethods
  36 // Removing nmethods from the code cache includes two operations
  37 //  1) mark active nmethods
  38 //     Is done in 'mark_active_nmethods()'. This function is called at a
  39 //     safepoint and marks all nmethods that are active on a thread's stack.
  40 //  2) sweep nmethods
  41 //     Is done in sweep_code_cache(). This function is the only place in the
  42 //     sweeper where memory is reclaimed. Note that sweep_code_cache() is not
  43 //     called at a safepoint. However, sweep_code_cache() stops executing if
  44 //     another thread requests a safepoint. Consequently, 'mark_active_nmethods()'
  45 //     and sweep_code_cache() cannot execute at the same time.
  46 //     To reclaim memory, nmethods are first marked as 'not-entrant'. Methods can
  47 //     be made not-entrant by (i) the sweeper, (ii) deoptimization, (iii) dependency
  48 //     invalidation, and (iv) being replaced be a different method version (tiered
  49 //     compilation). Not-entrant nmethod cannot be called by Java threads, but they
  50 //     can still be active on the stack. To ensure that active nmethod are not reclaimed,
  51 //     we have to wait until the next marking phase has completed. If a not-entrant
  52 //     nmethod was NOT marked as active, it can be converted to 'zombie' state. To safely
  53 //     remove the nmethod, all inline caches (IC) that point to the the nmethod must be
  54 //     cleared. After that, the nmethod can be evicted from the code cache. Each nmethod's
  55 //     state change happens during separate sweeps. It may take at least 3 sweeps before an
  56 //     nmethod's space is freed.
  57 
  58 class NMethodSweeper : public AllStatic {
  59  private:
  60   enum MethodStateChange {
  61     None,
  62     MadeZombie,
  63     MarkedForReclamation,
  64     Flushed
  65   };
  66   static long      _traversals;                   // Stack scan count, also sweep ID.
  67   static long      _total_nof_code_cache_sweeps;  // Total number of full sweeps of the code cache
  68   static long      _time_counter;                 // Virtual time used to periodically invoke sweeper
  69   static long      _last_sweep;                   // Value of _time_counter when the last sweep happened
  70   static NMethodIterator _current;                // Current nmethod
  71   static int       _seen;                         // Nof. nmethod we have currently processed in current pass of CodeCache
  72 
  73   static volatile int  _sweep_started;            // Flag to control conc sweeper

  28 class WhiteBox;
  29 
  30 #include "code/codeCache.hpp"
  31 #include "utilities/ticks.hpp"
  32 
  33 // An NmethodSweeper is an incremental cleaner for:
  34 //    - cleanup inline caches
  35 //    - reclamation of nmethods
  36 // Removing nmethods from the code cache includes two operations
  37 //  1) mark active nmethods
  38 //     Is done in 'mark_active_nmethods()'. This function is called at a
  39 //     safepoint and marks all nmethods that are active on a thread's stack.
  40 //  2) sweep nmethods
  41 //     Is done in sweep_code_cache(). This function is the only place in the
  42 //     sweeper where memory is reclaimed. Note that sweep_code_cache() is not
  43 //     called at a safepoint. However, sweep_code_cache() stops executing if
  44 //     another thread requests a safepoint. Consequently, 'mark_active_nmethods()'
  45 //     and sweep_code_cache() cannot execute at the same time.
  46 //     To reclaim memory, nmethods are first marked as 'not-entrant'. Methods can
  47 //     be made not-entrant by (i) the sweeper, (ii) deoptimization, (iii) dependency
  48 //     invalidation, and (iv) being replaced by a different method version (tiered
  49 //     compilation). Not-entrant nmethods cannot be called by Java threads, but they
  50 //     can still be active on the stack. To ensure that active nmethods are not reclaimed,
  51 //     we have to wait until the next marking phase has completed. If a not-entrant
  52 //     nmethod was NOT marked as active, it can be converted to 'zombie' state. To safely
  53 //     remove the nmethod, all inline caches (IC) that point to the nmethod must be
  54 //     cleared. After that, the nmethod can be evicted from the code cache. Each nmethod's
  55 //     state change happens during separate sweeps. It may take at least 3 sweeps before an
  56 //     nmethod's space is freed.
  57 
  58 class NMethodSweeper : public AllStatic {
  59  private:
  60   enum MethodStateChange {
  61     None,
  62     MadeZombie,
  63     MarkedForReclamation,
  64     Flushed
  65   };
  66   static long      _traversals;                   // Stack scan count, also sweep ID.
  67   static long      _total_nof_code_cache_sweeps;  // Total number of full sweeps of the code cache
  68   static long      _time_counter;                 // Virtual time used to periodically invoke sweeper
  69   static long      _last_sweep;                   // Value of _time_counter when the last sweep happened
  70   static NMethodIterator _current;                // Current nmethod
  71   static int       _seen;                         // Nof. nmethod we have currently processed in current pass of CodeCache
  72 
  73   static volatile int  _sweep_started;            // Flag to control conc sweeper