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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