sweeper.hpp revision 9111:a41fe5ffa839 
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24
25#ifndef SHARE_VM_RUNTIME_SWEEPER_HPP
26#define SHARE_VM_RUNTIME_SWEEPER_HPP
27
28class 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
58class 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
74  static volatile bool _should_sweep;             // Indicates if we should invoke the sweeper
75  static volatile bool _force_sweep;              // Indicates if we should force a sweep
76  static volatile int _bytes_changed;             // Counts the total nmethod size if the nmethod changed from:
77                                                  //   1) alive       -> not_entrant
78                                                  //   2) not_entrant -> zombie
79                                                  //   3) zombie      -> marked_for_reclamation
80  // Stat counters
81  static long      _total_nof_methods_reclaimed;    // Accumulated nof methods flushed
82  static long      _total_nof_c2_methods_reclaimed; // Accumulated nof C2-compiled methods flushed
83  static size_t    _total_flushed_size;             // Total size of flushed methods
84  static int       _hotness_counter_reset_val;
85
86  static Tickspan  _total_time_sweeping;          // Accumulated time sweeping
87  static Tickspan  _total_time_this_sweep;        // Total time this sweep
88  static Tickspan  _peak_sweep_time;              // Peak time for a full sweep
89  static Tickspan  _peak_sweep_fraction_time;     // Peak time sweeping one fraction
90
91  static Monitor*  _stat_lock;
92
93  static MethodStateChange process_nmethod(nmethod *nm);
94  static void              release_nmethod(nmethod* nm);
95
96  static void init_sweeper_log() NOT_DEBUG_RETURN;
97  static bool wait_for_stack_scanning();
98  static void sweep_code_cache();
99  static void handle_safepoint_request();
100  static void do_stack_scanning();
101  static void possibly_sweep();
102 public:
103  static long traversal_count()              { return _traversals; }
104  static int  total_nof_methods_reclaimed()  { return _total_nof_methods_reclaimed; }
105  static const Tickspan total_time_sweeping()      { return _total_time_sweeping; }
106  static const Tickspan peak_sweep_time()          { return _peak_sweep_time; }
107  static const Tickspan peak_sweep_fraction_time() { return _peak_sweep_fraction_time; }
108  static void log_sweep(const char* msg, const char* format = NULL, ...) ATTRIBUTE_PRINTF(2, 3);
109
110
111#ifdef ASSERT
112  static bool is_sweeping(nmethod* which) { return _current.method() == which; }
113  // Keep track of sweeper activity in the ring buffer
114  static void record_sweep(nmethod* nm, int line);
115  static void report_events(int id, address entry);
116  static void report_events();
117#endif
118
119  static void mark_active_nmethods();      // Invoked at the end of each safepoint
120  static void sweeper_loop();
121  static void notify(int code_blob_type);  // Possibly start the sweeper thread.
122  static void force_sweep();
123
124  static int hotness_counter_reset_val();
125  static void report_state_change(nmethod* nm);
126  static void possibly_enable_sweeper();
127  static void possibly_flush(nmethod* nm);
128  static void print();   // Printing/debugging
129};
130
131#endif // SHARE_VM_RUNTIME_SWEEPER_HPP
132