1 /*
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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 three 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'. Not-entrant
42 // nmethod cannot be called by Java threads, but they can still be active on the
43 // stack. To ensure that active nmethod are not reclaimed, we have to wait until the
44 // next marking phase has completed. If a not-entrant nmethod was NOT marked as active,
45 // it can be converted to 'zombie' state. To safely remove the nmethod, all inline caches
46 // (IC) that point to the the nmethod must be cleared. After that, the nmethod can be
47 // evicted from the code cache.
48 // 3) code cache flushing
49 // Is done in 'speculative_disconnect_nmethods()' and performed as a VM operation.
50 // Code cache flushing is performed as a last resort to clean the code cache. Flushing
51 // is performed in two steps. First, a subset of nmethods is selected for eviction. The
52 // selected nmethods are 'speculatively disconnected, i.e., the methods are added to a
53 // linked list AND the method's code pointer is set to null (nm->method()->code() = NULL)
54 // If the compiler tries to compile the disconnected nmethods (the compiler has to, since
55 // method()->code() == NULL), the compiler first searches the linked list where speculatively
56 // disconnected nmethods are stored. If the compiler finds the nmethod, the compiler 're-animates'
57 // the nmethod (restores the code pointer). If not, the method is removed by normal sweeping.
58
59 class NMethodSweeper : public AllStatic {
60 static long _traversals; // Stack scan count, also sweep ID.
61 static nmethod* _current; // Current nmethod
62 static int _seen; // Nof. nmethod we have currently processed in current pass of CodeCache
63 static int _flushed_count; // Nof. nmethods flushed in current sweep
64 static int _zombified_count; // Nof. nmethods made zombie in current sweep
65 static int _marked_count; // Nof. nmethods marked for reclaim in current sweep
66
67 static volatile int _invocations; // No. of invocations left until we are completed with this pass
68 static volatile int _sweep_started; // Flag to control conc sweeper
69
70 //The following are reset in mark_active_nmethods and synchronized by the safepoint
71 static bool _request_mark_phase; // Indicates that a change has happend and we need another mark pahse,
72 // always checked and reset at a safepoint so memory will be in sync.
73 static int _locked_seen; // Number of locked nmethods encountered during the scan
74 static int _not_entrant_seen_on_stack; // Number of not entrant nmethod were are still on stack
75 static jint _flush_token; // token that guards method flushing, making sure it is executed only once.
76
77 // These are set during a flush, a VM-operation
78 static long _last_flush_traversal_id; // trav number at last flush unloading
79 static jlong _last_full_flush_time; // timestamp of last emergency unloading
80
81 // Stat counters
82 static int _number_of_flushes; // Total of full traversals caused by full cache
83 static int _total_nof_methods_reclaimed; // Accumulated nof methods flushed
84 static jlong _total_time_sweeping; // Accumulated time sweeping
85 static jlong _total_time_this_sweep; // Total time this sweep
86 static jlong _peak_sweep_time; // Peak time for a full sweep
87 static jlong _peak_sweep_fraction_time; // Peak time sweeping one fraction
88 static jlong _total_disconnect_time; // Total time cleaning code mem
89 static jlong _peak_disconnect_time; // Peak time cleaning code mem
90
91 static void process_nmethod(nmethod *nm);
92 static void release_nmethod(nmethod* nm);
93
94 static void log_sweep(const char* msg, const char* format = NULL, ...);
95 static bool sweep_in_progress();
96 static void sweep_code_cache();
97 static void request_nmethod_marking() { _request_mark_phase = true; }
98 static void reset_nmethod_marking() { _request_mark_phase = false; }
99 static bool need_marking_phase() { return _request_mark_phase; }
100
101 static int _hotness_counter_reset_val;
102
103 public:
104 static long traversal_count() { return _traversals; }
105 static int number_of_flushes() { return _number_of_flushes; }
106 static int total_nof_methods_reclaimed() { return _total_nof_methods_reclaimed; }
107 static jlong total_time_sweeping() { return _total_time_sweeping; }
108 static jlong peak_sweep_time() { return _peak_sweep_time; }
109 static jlong peak_sweep_fraction_time() { return _peak_sweep_fraction_time; }
110 static jlong total_disconnect_time() { return _total_disconnect_time; }
111 static jlong peak_disconnect_time() { return _peak_disconnect_time; }
112
113 #ifdef ASSERT
114 static bool is_sweeping(nmethod* which) { return _current == which; }
115 // Keep track of sweeper activity in the ring buffer
116 static void record_sweep(nmethod* nm, int line);
117 static void report_events(int id, address entry);
118 static void report_events();
119 #endif
120
121 static void mark_active_nmethods(); // Invoked at the end of each safepoint
122 static void possibly_sweep(); // Compiler threads call this to sweep
123
124 static int sort_nmethods_by_hotness(nmethod** nm1, nmethod** nm2);
125 static int get_hotness_counter_reset_val();
126
127 static void notify() {
128 // Request a new sweep of the code cache from the beginning. No
129 // need to synchronize the setting of this flag since it only
130 // changes to false at safepoint so we can never overwrite it with false.
131 request_nmethod_marking();
132 }
133
134 static void handle_full_code_cache(bool is_full); // Called by compilers who fail to allocate
135 static void speculative_disconnect_nmethods(bool was_full); // Called by vm op to deal with alloc failure
136 };
137
138 #endif // SHARE_VM_RUNTIME_SWEEPER_HPP