1 /*
2 * Copyright (c) 1997, 2010, 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 //
26 // Safepoint synchronization
27 ////
28 // The VMThread or CMS_thread uses the SafepointSynchronize::begin/end
29 // methods to enter/exit a safepoint region. The begin method will roll
30 // all JavaThreads forward to a safepoint.
31 //
32 // JavaThreads must use the ThreadSafepointState abstraction (defined in
33 // thread.hpp) to indicate that that they are at a safepoint.
34 //
35 // The Mutex/Condition variable and ObjectLocker classes calls the enter/
36 // exit safepoint methods, when a thread is blocked/restarted. Hence, all mutex exter/
37 // exit points *must* be at a safepoint.
38
39
40 class ThreadSafepointState;
41 class SnippetCache;
42 class nmethod;
43
44 //
45 // Implements roll-forward to safepoint (safepoint synchronization)
46 //
47 class SafepointSynchronize : AllStatic {
48 public:
49 enum SynchronizeState {
50 _not_synchronized = 0, // Threads not synchronized at a safepoint
51 // Keep this value 0. See the coment in do_call_back()
52 _synchronizing = 1, // Synchronizing in progress
53 _synchronized = 2 // All Java threads are stopped at a safepoint. Only VM thread is running
54 };
55
56 enum SafepointingThread {
57 _null_thread = 0,
58 _vm_thread = 1,
59 _other_thread = 2
60 };
61
62 enum SafepointTimeoutReason {
63 _spinning_timeout = 0,
64 _blocking_timeout = 1
65 };
66
67 typedef struct {
68 float _time_stamp; // record when the current safepoint occurs in seconds
69 int _vmop_type; // type of VM operation triggers the safepoint
70 int _nof_total_threads; // total number of Java threads
71 int _nof_initial_running_threads; // total number of initially seen running threads
72 int _nof_threads_wait_to_block; // total number of threads waiting for to block
73 bool _page_armed; // true if polling page is armed, false otherwise
74 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap
75 jlong _time_to_spin; // total time in millis spent in spinning
76 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block
77 jlong _time_to_do_cleanups; // total time in millis spent in performing cleanups
78 jlong _time_to_sync; // total time in millis spent in getting to _synchronized
79 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself
80 } SafepointStats;
81
82 private:
83 static volatile SynchronizeState _state; // Threads might read this flag directly, without acquireing the Threads_lock
84 static volatile int _waiting_to_block; // number of threads we are waiting for to block
85
86 // This counter is used for fast versions of jni_Get<Primitive>Field.
87 // An even value means there is no ongoing safepoint operations.
88 // The counter is incremented ONLY at the beginning and end of each
89 // safepoint. The fact that Threads_lock is held throughout each pair of
90 // increments (at the beginning and end of each safepoint) guarantees
91 // race freedom.
92 public:
93 static volatile int _safepoint_counter;
94 private:
95 static long _end_of_last_safepoint; // Time of last safepoint in milliseconds
96
97 // statistics
98 static jlong _safepoint_begin_time; // time when safepoint begins
99 static SafepointStats* _safepoint_stats; // array of SafepointStats struct
100 static int _cur_stat_index; // current index to the above array
101 static julong _safepoint_reasons[]; // safepoint count for each VM op
102 static julong _coalesced_vmop_count; // coalesced vmop count
103 static jlong _max_sync_time; // maximum sync time in nanos
104 static jlong _max_vmop_time; // maximum vm operation time in nanos
105 static float _ts_of_current_safepoint; // time stamp of current safepoint in seconds
106
107 static void begin_statistics(int nof_threads, int nof_running);
108 static void update_statistics_on_spin_end();
109 static void update_statistics_on_sync_end(jlong end_time);
110 static void update_statistics_on_cleanup_end(jlong end_time);
111 static void end_statistics(jlong end_time);
112 static void print_statistics();
113 inline static void inc_page_trap_count() {
114 Atomic::inc(&_safepoint_stats[_cur_stat_index]._nof_threads_hit_page_trap);
115 }
116
117 // For debug long safepoint
118 static void print_safepoint_timeout(SafepointTimeoutReason timeout_reason);
119
120 public:
121
122 // Main entry points
123
124 // Roll all threads forward to safepoint. Must be called by the
125 // VMThread or CMS_thread.
126 static void begin();
127 static void end(); // Start all suspended threads again...
128
129 static bool safepoint_safe(JavaThread *thread, JavaThreadState state);
130
131 // Query
132 inline static bool is_at_safepoint() { return _state == _synchronized; }
133 inline static bool is_synchronizing() { return _state == _synchronizing; }
134
135 inline static bool do_call_back() {
136 return (_state != _not_synchronized);
137 }
138
139 // Called when a thread volantary blocks
140 static void block(JavaThread *thread);
141 static void signal_thread_at_safepoint() { _waiting_to_block--; }
142
143 // Exception handling for page polling
144 static void handle_polling_page_exception(JavaThread *thread);
145
146 // VM Thread interface for determining safepoint rate
147 static long last_non_safepoint_interval() {
148 return os::javaTimeMillis() - _end_of_last_safepoint;
149 }
150 static long end_of_last_safepoint() {
151 return _end_of_last_safepoint;
152 }
153 static bool is_cleanup_needed();
154 static void do_cleanup_tasks();
155
156 // debugging
157 static void print_state() PRODUCT_RETURN;
158 static void safepoint_msg(const char* format, ...) PRODUCT_RETURN;
159
160 static void deferred_initialize_stat();
161 static void print_stat_on_exit();
162 inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
163
164 static void set_is_at_safepoint() { _state = _synchronized; }
165 static void set_is_not_at_safepoint() { _state = _not_synchronized; }
166
167 // assembly support
168 static address address_of_state() { return (address)&_state; }
169
170 static address safepoint_counter_addr() { return (address)&_safepoint_counter; }
171 };
172
173 // State class for a thread suspended at a safepoint
174 class ThreadSafepointState: public CHeapObj {
175 public:
176 // These states are maintained by VM thread while threads are being brought
177 // to a safepoint. After SafepointSynchronize::end(), they are reset to
178 // _running.
179 enum suspend_type {
180 _running = 0, // Thread state not yet determined (i.e., not at a safepoint yet)
181 _at_safepoint = 1, // Thread at a safepoint (f.ex., when blocked on a lock)
182 _call_back = 2 // Keep executing and wait for callback (if thread is in interpreted or vm)
183 };
184 private:
185 volatile bool _at_poll_safepoint; // At polling page safepoint (NOT a poll return safepoint)
186 // Thread has called back the safepoint code (for debugging)
187 bool _has_called_back;
188
189 JavaThread * _thread;
190 volatile suspend_type _type;
191 JavaThreadState _orig_thread_state;
192
193
194 public:
195 ThreadSafepointState(JavaThread *thread);
196
197 // examine/roll-forward/restart
198 void examine_state_of_thread();
199 void roll_forward(suspend_type type);
200 void restart();
201
202 // Query
203 JavaThread* thread() const { return _thread; }
204 suspend_type type() const { return _type; }
205 bool is_running() const { return (_type==_running); }
206 JavaThreadState orig_thread_state() const { return _orig_thread_state; }
207
208 // Support for safepoint timeout (debugging)
209 bool has_called_back() const { return _has_called_back; }
210 void set_has_called_back(bool val) { _has_called_back = val; }
211 bool is_at_poll_safepoint() { return _at_poll_safepoint; }
212 void set_at_poll_safepoint(bool val) { _at_poll_safepoint = val; }
213
214 void handle_polling_page_exception();
215
216 // debugging
217 void print_on(outputStream* st) const;
218 void print() const { print_on(tty); }
219
220 // Initialize
221 static void create(JavaThread *thread);
222 static void destroy(JavaThread *thread);
223
224 void safepoint_msg(const char* format, ...) {
225 if (ShowSafepointMsgs) {
226 va_list ap;
227 va_start(ap, format);
228 tty->vprint_cr(format, ap);
229 va_end(ap);
230 }
231 }
232 };
233
234