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 #ifndef SHARE_VM_RUNTIME_SAFEPOINT_HPP
26 #define SHARE_VM_RUNTIME_SAFEPOINT_HPP
27
28 #include "asm/assembler.hpp"
29 #include "code/nmethod.hpp"
30 #include "memory/allocation.hpp"
31 #include "runtime/extendedPC.hpp"
32 #include "runtime/os.hpp"
33 #include "utilities/ostream.hpp"
34
35 //
36 // Safepoint synchronization
37 ////
38 // The VMThread or CMS_thread uses the SafepointSynchronize::begin/end
39 // methods to enter/exit a safepoint region. The begin method will roll
40 // all JavaThreads forward to a safepoint.
41 //
42 // JavaThreads must use the ThreadSafepointState abstraction (defined in
43 // thread.hpp) to indicate that that they are at a safepoint.
44 //
45 // The Mutex/Condition variable and ObjectLocker classes calls the enter/
46 // exit safepoint methods, when a thread is blocked/restarted. Hence, all mutex exter/
47 // exit points *must* be at a safepoint.
48
49
50 class ThreadSafepointState;
51 class SnippetCache;
52 class nmethod;
53
54 //
55 // Implements roll-forward to safepoint (safepoint synchronization)
56 //
57 class SafepointSynchronize : AllStatic {
58 public:
59 enum SynchronizeState {
60 _not_synchronized = 0, // Threads not synchronized at a safepoint
61 // Keep this value 0. See the coment in do_call_back()
62 _synchronizing = 1, // Synchronizing in progress
63 _synchronized = 2 // All Java threads are stopped at a safepoint. Only VM thread is running
64 };
65
66 enum SafepointingThread {
67 _null_thread = 0,
68 _vm_thread = 1,
69 _other_thread = 2
70 };
71
72 enum SafepointTimeoutReason {
73 _spinning_timeout = 0,
74 _blocking_timeout = 1
75 };
76
77 typedef struct {
78 float _time_stamp; // record when the current safepoint occurs in seconds
79 int _vmop_type; // type of VM operation triggers the safepoint
80 int _nof_total_threads; // total number of Java threads
81 int _nof_initial_running_threads; // total number of initially seen running threads
82 int _nof_threads_wait_to_block; // total number of threads waiting for to block
83 bool _page_armed; // true if polling page is armed, false otherwise
84 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap
85 jlong _time_to_spin; // total time in millis spent in spinning
86 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block
87 jlong _time_to_do_cleanups; // total time in millis spent in performing cleanups
88 jlong _time_to_sync; // total time in millis spent in getting to _synchronized
89 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself
90 } SafepointStats;
91
92 private:
93 static volatile SynchronizeState _state; // Threads might read this flag directly, without acquireing the Threads_lock
94 static volatile int _waiting_to_block; // number of threads we are waiting for to block
95
96 // This counter is used for fast versions of jni_Get<Primitive>Field.
97 // An even value means there is no ongoing safepoint operations.
98 // The counter is incremented ONLY at the beginning and end of each
99 // safepoint. The fact that Threads_lock is held throughout each pair of
100 // increments (at the beginning and end of each safepoint) guarantees
101 // race freedom.
102 public:
103 static volatile int _safepoint_counter;
104 private:
105 static long _end_of_last_safepoint; // Time of last safepoint in milliseconds
106
107 // statistics
108 static jlong _safepoint_begin_time; // time when safepoint begins
109 static SafepointStats* _safepoint_stats; // array of SafepointStats struct
110 static int _cur_stat_index; // current index to the above array
111 static julong _safepoint_reasons[]; // safepoint count for each VM op
112 static julong _coalesced_vmop_count; // coalesced vmop count
113 static jlong _max_sync_time; // maximum sync time in nanos
114 static jlong _max_vmop_time; // maximum vm operation time in nanos
115 static float _ts_of_current_safepoint; // time stamp of current safepoint in seconds
116
117 static void begin_statistics(int nof_threads, int nof_running);
118 static void update_statistics_on_spin_end();
119 static void update_statistics_on_sync_end(jlong end_time);
120 static void update_statistics_on_cleanup_end(jlong end_time);
121 static void end_statistics(jlong end_time);
122 static void print_statistics();
123 inline static void inc_page_trap_count() {
124 Atomic::inc(&_safepoint_stats[_cur_stat_index]._nof_threads_hit_page_trap);
125 }
126
127 // For debug long safepoint
128 static void print_safepoint_timeout(SafepointTimeoutReason timeout_reason);
129
130 public:
131
132 // Main entry points
133
134 // Roll all threads forward to safepoint. Must be called by the
135 // VMThread or CMS_thread.
136 static void begin();
137 static void end(); // Start all suspended threads again...
138
139 static bool safepoint_safe(JavaThread *thread, JavaThreadState state);
140
141 // Query
142 inline static bool is_at_safepoint() { return _state == _synchronized; }
143 inline static bool is_synchronizing() { return _state == _synchronizing; }
144
145 inline static bool do_call_back() {
146 return (_state != _not_synchronized);
147 }
148
149 // Called when a thread volantary blocks
150 static void block(JavaThread *thread);
151 static void signal_thread_at_safepoint() { _waiting_to_block--; }
152
153 // Exception handling for page polling
154 static void handle_polling_page_exception(JavaThread *thread);
155
156 // VM Thread interface for determining safepoint rate
157 static long last_non_safepoint_interval() {
158 return os::javaTimeMillis() - _end_of_last_safepoint;
159 }
160 static long end_of_last_safepoint() {
161 return _end_of_last_safepoint;
162 }
163 static bool is_cleanup_needed();
164 static void do_cleanup_tasks();
165
166 // debugging
167 static void print_state() PRODUCT_RETURN;
168 static void safepoint_msg(const char* format, ...) PRODUCT_RETURN;
169
170 static void deferred_initialize_stat();
171 static void print_stat_on_exit();
172 inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
173
174 static void set_is_at_safepoint() { _state = _synchronized; }
175 static void set_is_not_at_safepoint() { _state = _not_synchronized; }
176
177 // assembly support
178 static address address_of_state() { return (address)&_state; }
179
180 static address safepoint_counter_addr() { return (address)&_safepoint_counter; }
181 };
182
183 // State class for a thread suspended at a safepoint
184 class ThreadSafepointState: public CHeapObj {
185 public:
186 // These states are maintained by VM thread while threads are being brought
187 // to a safepoint. After SafepointSynchronize::end(), they are reset to
188 // _running.
189 enum suspend_type {
190 _running = 0, // Thread state not yet determined (i.e., not at a safepoint yet)
191 _at_safepoint = 1, // Thread at a safepoint (f.ex., when blocked on a lock)
192 _call_back = 2 // Keep executing and wait for callback (if thread is in interpreted or vm)
193 };
194 private:
195 volatile bool _at_poll_safepoint; // At polling page safepoint (NOT a poll return safepoint)
196 // Thread has called back the safepoint code (for debugging)
197 bool _has_called_back;
198
199 JavaThread * _thread;
200 volatile suspend_type _type;
201 JavaThreadState _orig_thread_state;
202
203
204 public:
205 ThreadSafepointState(JavaThread *thread);
206
207 // examine/roll-forward/restart
208 void examine_state_of_thread();
209 void roll_forward(suspend_type type);
210 void restart();
211
212 // Query
213 JavaThread* thread() const { return _thread; }
214 suspend_type type() const { return _type; }
215 bool is_running() const { return (_type==_running); }
216 JavaThreadState orig_thread_state() const { return _orig_thread_state; }
217
218 // Support for safepoint timeout (debugging)
219 bool has_called_back() const { return _has_called_back; }
220 void set_has_called_back(bool val) { _has_called_back = val; }
221 bool is_at_poll_safepoint() { return _at_poll_safepoint; }
222 void set_at_poll_safepoint(bool val) { _at_poll_safepoint = val; }
223
224 void handle_polling_page_exception();
225
226 // debugging
227 void print_on(outputStream* st) const;
228 void print() const { print_on(tty); }
229
230 // Initialize
231 static void create(JavaThread *thread);
232 static void destroy(JavaThread *thread);
233
234 void safepoint_msg(const char* format, ...) {
235 if (ShowSafepointMsgs) {
236 va_list ap;
237 va_start(ap, format);
238 tty->vprint_cr(format, ap);
239 va_end(ap);
240 }
241 }
242 };
243
244
245
246 #endif // SHARE_VM_RUNTIME_SAFEPOINT_HPP