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comparison src/share/vm/runtime/safepoint.hpp @ 0:a61af66fc99e jdk7-b24

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author duke
date Sat, 01 Dec 2007 00:00:00 +0000
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1 /*
2 * Copyright 1997-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any 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 int _vmop_type; // type of VM operation triggers the safepoint
69 int _nof_total_threads; // total number of Java threads
70 int _nof_initial_running_threads; // total number of initially seen running threads
71 int _nof_threads_wait_to_block; // total number of threads waiting for to block
72 bool _page_armed; // true if polling page is armed, false otherwise
73 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap
74 jlong _time_to_spin; // total time in millis spent in spinning
75 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block
76 jlong _time_to_sync; // total time in millis spent in getting to _synchronized
77 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself
78 jlong _time_elapsed_since_last_safepoint; // time elasped since last safepoint
79 } SafepointStats;
80
81 private:
82 static volatile SynchronizeState _state; // Threads might read this flag directly, without acquireing the Threads_lock
83 static volatile int _waiting_to_block; // No. of threads we are waiting for to block.
84
85 // This counter is used for fast versions of jni_Get<Primitive>Field.
86 // An even value means there is no ongoing safepoint operations.
87 // The counter is incremented ONLY at the beginning and end of each
88 // safepoint. The fact that Threads_lock is held throughout each pair of
89 // increments (at the beginning and end of each safepoint) guarantees
90 // race freedom.
91 public:
92 static volatile int _safepoint_counter;
93 private:
94
95 static jlong _last_safepoint; // Time of last safepoint
96
97 // statistics
98 static SafepointStats* _safepoint_stats; // array of SafepointStats struct
99 static int _cur_stat_index; // current index to the above array
100 static julong _safepoint_reasons[]; // safepoint count for each VM op
101 static julong _coalesced_vmop_count;// coalesced vmop count
102 static jlong _max_sync_time; // maximum sync time in nanos
103
104 static void begin_statistics(int nof_threads, int nof_running);
105 static void update_statistics_on_spin_end();
106 static void update_statistics_on_sync_end(jlong end_time);
107 static void end_statistics(jlong end_time);
108 static void print_statistics();
109 inline static void inc_page_trap_count() {
110 Atomic::inc(&_safepoint_stats[_cur_stat_index]._nof_threads_hit_page_trap);
111 }
112
113 // For debug long safepoint
114 static void print_safepoint_timeout(SafepointTimeoutReason timeout_reason);
115
116 public:
117
118 // Main entry points
119
120 // Roll all threads forward to safepoint. Must be called by the
121 // VMThread or CMS_thread.
122 static void begin();
123 static void end(); // Start all suspended threads again...
124
125 static bool safepoint_safe(JavaThread *thread, JavaThreadState state);
126
127 // Query
128 inline static bool is_at_safepoint() { return _state == _synchronized; }
129 inline static bool is_synchronizing() { return _state == _synchronizing; }
130
131 inline static bool do_call_back() {
132 return (_state != _not_synchronized);
133 }
134
135 // Called when a thread volantary blocks
136 static void block(JavaThread *thread);
137 static void signal_thread_at_safepoint() { _waiting_to_block--; }
138
139 // Exception handling for page polling
140 static void handle_polling_page_exception(JavaThread *thread);
141
142 // VM Thread interface for determining safepoint rate
143 static long last_non_safepoint_interval() { return os::javaTimeMillis() - _last_safepoint; }
144 static bool is_cleanup_needed();
145 static void do_cleanup_tasks();
146
147 // debugging
148 static void print_state() PRODUCT_RETURN;
149 static void safepoint_msg(const char* format, ...) PRODUCT_RETURN;
150
151 static void deferred_initialize_stat();
152 static void print_stat_on_exit();
153 inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
154
155 static void set_is_at_safepoint() { _state = _synchronized; }
156 static void set_is_not_at_safepoint() { _state = _not_synchronized; }
157
158 // assembly support
159 static address address_of_state() { return (address)&_state; }
160
161 static address safepoint_counter_addr() { return (address)&_safepoint_counter; }
162 };
163
164 // State class for a thread suspended at a safepoint
165 class ThreadSafepointState: public CHeapObj {
166 public:
167 // These states are maintained by VM thread while threads are being brought
168 // to a safepoint. After SafepointSynchronize::end(), they are reset to
169 // _running.
170 enum suspend_type {
171 _running = 0, // Thread state not yet determined (i.e., not at a safepoint yet)
172 _at_safepoint = 1, // Thread at a safepoint (f.ex., when blocked on a lock)
173 _call_back = 2 // Keep executing and wait for callback (if thread is in interpreted or vm)
174 };
175 private:
176 volatile bool _at_poll_safepoint; // At polling page safepoint (NOT a poll return safepoint)
177 // Thread has called back the safepoint code (for debugging)
178 bool _has_called_back;
179
180 JavaThread * _thread;
181 volatile suspend_type _type;
182
183
184 public:
185 ThreadSafepointState(JavaThread *thread);
186
187 // examine/roll-forward/restart
188 void examine_state_of_thread();
189 void roll_forward(suspend_type type);
190 void restart();
191
192 // Query
193 JavaThread* thread() const { return _thread; }
194 suspend_type type() const { return _type; }
195 bool is_running() const { return (_type==_running); }
196
197 // Support for safepoint timeout (debugging)
198 bool has_called_back() const { return _has_called_back; }
199 void set_has_called_back(bool val) { _has_called_back = val; }
200 bool is_at_poll_safepoint() { return _at_poll_safepoint; }
201 void set_at_poll_safepoint(bool val) { _at_poll_safepoint = val; }
202
203 void handle_polling_page_exception();
204
205 // debugging
206 void print_on(outputStream* st) const;
207 void print() const { print_on(tty); }
208
209 // Initialize
210 static void create(JavaThread *thread);
211 static void destroy(JavaThread *thread);
212
213 void safepoint_msg(const char* format, ...) {
214 if (ShowSafepointMsgs) {
215 va_list ap;
216 va_start(ap, format);
217 tty->vprint_cr(format, ap);
218 va_end(ap);
219 }
220 }
221 };
222
223 //
224 // CounterDecay
225 //
226 // Interates through invocation counters and decrements them. This
227 // is done at each safepoint.
228 //
229 class CounterDecay : public AllStatic {
230 static jlong _last_timestamp;
231 public:
232 static void decay();
233 static bool is_decay_needed() { return (os::javaTimeMillis() - _last_timestamp) > CounterDecayMinIntervalLength; }
234 };