sweeper.hpp revision 11079:69d081845165 
1/*
2 * Copyright (c) 1997, 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
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).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
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 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
58class NMethodSweeper : public AllStatic {
59 private:
60  enum MethodStateChange {
61    None,
62    MadeZombie,
63    Flushed
64  };
65  static long      _traversals;                   // Stack scan count, also sweep ID.
66  static long      _total_nof_code_cache_sweeps;  // Total number of full sweeps of the code cache
67  static long      _time_counter;                 // Virtual time used to periodically invoke sweeper
68  static long      _last_sweep;                   // Value of _time_counter when the last sweep happened
69  static CompiledMethodIterator _current;         // Current compiled method
70  static int       _seen;                         // Nof. nmethod we have currently processed in current pass of CodeCache
71
72  static volatile int  _sweep_started;            // Flag to control conc sweeper
73  static volatile bool _should_sweep;             // Indicates if we should invoke the sweeper
74  static volatile bool _force_sweep;              // Indicates if we should force a sweep
75  static volatile int _bytes_changed;             // Counts the total nmethod size if the nmethod changed from:
76                                                  //   1) alive       -> not_entrant
77                                                  //   2) not_entrant -> zombie
78  // Stat counters
79  static long      _total_nof_methods_reclaimed;    // Accumulated nof methods flushed
80  static long      _total_nof_c2_methods_reclaimed; // Accumulated nof C2-compiled methods flushed
81  static size_t    _total_flushed_size;             // Total size of flushed methods
82  static int       _hotness_counter_reset_val;
83
84  static Tickspan  _total_time_sweeping;          // Accumulated time sweeping
85  static Tickspan  _total_time_this_sweep;        // Total time this sweep
86  static Tickspan  _peak_sweep_time;              // Peak time for a full sweep
87  static Tickspan  _peak_sweep_fraction_time;     // Peak time sweeping one fraction
88
89  static Monitor*  _stat_lock;
90
91  static MethodStateChange process_compiled_method(CompiledMethod *nm);
92  static void              release_compiled_method(CompiledMethod* nm);
93
94  static void init_sweeper_log() NOT_DEBUG_RETURN;
95  static bool wait_for_stack_scanning();
96  static void sweep_code_cache();
97  static void handle_safepoint_request();
98  static void do_stack_scanning();
99  static void possibly_sweep();
100 public:
101  static long traversal_count()              { return _traversals; }
102  static int  total_nof_methods_reclaimed()  { return _total_nof_methods_reclaimed; }
103  static const Tickspan total_time_sweeping()      { return _total_time_sweeping; }
104  static const Tickspan peak_sweep_time()          { return _peak_sweep_time; }
105  static const Tickspan peak_sweep_fraction_time() { return _peak_sweep_fraction_time; }
106  static void log_sweep(const char* msg, const char* format = NULL, ...) ATTRIBUTE_PRINTF(2, 3);
107
108
109#ifdef ASSERT
110  // Keep track of sweeper activity in the ring buffer
111  static void record_sweep(CompiledMethod* nm, int line);
112  static void report_events(int id, address entry);
113  static void report_events();
114#endif
115
116  static void mark_active_nmethods();      // Invoked at the end of each safepoint
117  static void sweeper_loop();
118  static void notify(int code_blob_type);  // Possibly start the sweeper thread.
119  static void force_sweep();
120
121  static int hotness_counter_reset_val();
122  static void report_state_change(nmethod* nm);
123  static void possibly_enable_sweeper();
124  static void possibly_flush(nmethod* nm);
125  static void print();   // Printing/debugging
126};
127
128#endif // SHARE_VM_RUNTIME_SWEEPER_HPP
129