1 /*
2 * Copyright (c) 2017, 2019, 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.
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23 */
24
25 #ifndef SHARE_RUNTIME_THREADSMR_HPP
26 #define SHARE_RUNTIME_THREADSMR_HPP
27
28 #include "memory/allocation.hpp"
29 #include "runtime/timer.hpp"
30
31 class JavaThread;
32 class Monitor;
33 class outputStream;
34 class Thread;
35 class ThreadClosure;
36
37 // Thread Safe Memory Reclamation (Thread-SMR) support.
38 //
39 // ThreadsListHandles are used to safely perform operations on one or more
40 // threads without the risk of the thread or threads exiting during the
41 // operation. It is no longer necessary to hold the Threads_lock to safely
42 // perform an operation on a target thread.
43 //
44 // There are several different ways to refer to java.lang.Thread objects
45 // so we have a few ways to get a protected JavaThread *:
46 //
47 // JNI jobject example:
48 // jobject jthread = ...;
49 // :
50 // ThreadsListHandle tlh;
51 // JavaThread* jt = NULL;
52 // bool is_alive = tlh.cv_internal_thread_to_JavaThread(jthread, &jt, NULL);
53 // if (is_alive) {
54 // : // do stuff with 'jt'...
55 // }
56 //
57 // JVM/TI jthread example:
58 // jthread thread = ...;
59 // :
60 // JavaThread* jt = NULL;
61 // ThreadsListHandle tlh;
62 // jvmtiError err = JvmtiExport::cv_external_thread_to_JavaThread(tlh.list(), thread, &jt, NULL);
63 // if (err != JVMTI_ERROR_NONE) {
64 // return err;
65 // }
66 // : // do stuff with 'jt'...
67 //
68 // JVM/TI oop example (this one should be very rare):
69 // oop thread_obj = ...;
70 // :
71 // JavaThread *jt = NULL;
72 // ThreadsListHandle tlh;
73 // jvmtiError err = JvmtiExport::cv_oop_to_JavaThread(tlh.list(), thread_obj, &jt);
74 // if (err != JVMTI_ERROR_NONE) {
75 // return err;
76 // }
77 // : // do stuff with 'jt'...
78 //
79 // A JavaThread * that is included in the ThreadsList that is held by
80 // a ThreadsListHandle is protected as long as the ThreadsListHandle
81 // remains in scope. The target JavaThread * may have logically exited,
82 // but that target JavaThread * will not be deleted until it is no
83 // longer protected by a ThreadsListHandle.
84
85
86 // SMR Support for the Threads class.
87 //
88 class ThreadsSMRSupport : AllStatic {
89 friend class VMStructs;
90 friend class SafeThreadsListPtr; // for _nested_thread_list_max, delete_notify(), release_stable_list_wake_up() access
91
92 // The coordination between ThreadsSMRSupport::release_stable_list() and
93 // ThreadsSMRSupport::smr_delete() uses the delete_lock in order to
94 // reduce the traffic on the Threads_lock.
95 static Monitor* delete_lock() { return ThreadsSMRDelete_lock; }
96
97 // The '_cnt', '_max' and '_times" fields are enabled via
98 // -XX:+EnableThreadSMRStatistics (see thread.cpp for a
99 // description about each field):
100 static uint _delete_lock_wait_cnt;
101 static uint _delete_lock_wait_max;
102 // The delete_notify flag is used for proper double-check
103 // locking in order to reduce the traffic on the system wide
104 // Thread-SMR delete_lock.
105 static volatile uint _delete_notify;
106 static volatile uint _deleted_thread_cnt;
107 static volatile uint _deleted_thread_time_max;
108 static volatile uint _deleted_thread_times;
109 static ThreadsList _bootstrap_list;
110 static ThreadsList* volatile _java_thread_list;
111 static uint64_t _java_thread_list_alloc_cnt;
112 static uint64_t _java_thread_list_free_cnt;
113 static uint _java_thread_list_max;
114 static uint _nested_thread_list_max;
115 static volatile uint _tlh_cnt;
116 static volatile uint _tlh_time_max;
117 static volatile uint _tlh_times;
118 static ThreadsList* _to_delete_list;
119 static uint _to_delete_list_cnt;
120 static uint _to_delete_list_max;
121
122 static ThreadsList *acquire_stable_list_fast_path(Thread *self);
123 static ThreadsList *acquire_stable_list_nested_path(Thread *self);
124 static void add_deleted_thread_times(uint add_value);
125 static void add_tlh_times(uint add_value);
126 static void clear_delete_notify();
127 static bool delete_notify();
128 static void free_list(ThreadsList* threads);
129 static void inc_deleted_thread_cnt();
130 static void inc_java_thread_list_alloc_cnt();
131 static void inc_tlh_cnt();
132 static bool is_a_protected_JavaThread(JavaThread *thread);
133 static void release_stable_list_wake_up(bool is_nested);
134 static void set_delete_notify();
135 static void threads_do(ThreadClosure *tc);
136 static void threads_do(ThreadClosure *tc, ThreadsList *list);
137 static void update_deleted_thread_time_max(uint new_value);
138 static void update_java_thread_list_max(uint new_value);
139 static void update_tlh_time_max(uint new_value);
140 static void verify_hazard_ptr_scanned(Thread *self, ThreadsList *threads);
141 static ThreadsList* xchg_java_thread_list(ThreadsList* new_list);
142
143 public:
144 static void add_thread(JavaThread *thread);
145 static ThreadsList* get_java_thread_list();
146 static bool is_a_protected_JavaThread_with_lock(JavaThread *thread);
147 static bool is_bootstrap_list(ThreadsList* list);
148 static void remove_thread(JavaThread *thread);
149 static void smr_delete(JavaThread *thread);
150 static void update_tlh_stats(uint millis);
151
152 // Logging and printing support:
153 static void log_statistics();
154 static void print_info_elements_on(outputStream* st, ThreadsList* t_list);
155 static void print_info_on(outputStream* st);
156 static void print_info_on(const Thread* thread, outputStream* st);
157 };
158
159 // A fast list of JavaThreads.
160 //
161 class ThreadsList : public CHeapObj<mtThread> {
162 friend class VMStructs;
163 friend class SafeThreadsListPtr; // for {dec,inc}_nested_handle_cnt() access
164 friend class ThreadsSMRSupport; // for _nested_handle_cnt, {add,remove}_thread(), {,set_}next_list() access
165
166 const uint _length;
167 ThreadsList* _next_list;
168 JavaThread *const *const _threads;
169 volatile intx _nested_handle_cnt;
170
171 template <class T>
172 void threads_do_dispatch(T *cl, JavaThread *const thread) const;
173
174 ThreadsList *next_list() const { return _next_list; }
175 void set_next_list(ThreadsList *list) { _next_list = list; }
176
177 void inc_nested_handle_cnt();
178 void dec_nested_handle_cnt();
179
180 static ThreadsList* add_thread(ThreadsList* list, JavaThread* java_thread);
181 static ThreadsList* remove_thread(ThreadsList* list, JavaThread* java_thread);
182
183 public:
184 ThreadsList(int entries);
185 ~ThreadsList();
186
187 template <class T>
188 void threads_do(T *cl) const;
189
190 uint length() const { return _length; }
191
192 JavaThread *const thread_at(uint i) const { return _threads[i]; }
193
194 JavaThread *const *threads() const { return _threads; }
195
196 // Returns -1 if target is not found.
197 int find_index_of_JavaThread(JavaThread* target);
198 JavaThread* find_JavaThread_from_java_tid(jlong java_tid) const;
199 bool includes(const JavaThread * const p) const;
200 };
201
202 // An abstract safe ptr to a ThreadsList comprising either a stable hazard ptr
203 // for leaves, or a retained reference count for nested uses. The user of this
204 // API does not need to know which mechanism is providing the safety.
205 class SafeThreadsListPtr {
206 friend class ThreadsListSetter;
207
208 SafeThreadsListPtr* _previous;
209 Thread* _thread;
210 ThreadsList* _list;
211 bool _has_ref_count;
212 bool _needs_release;
213
214 void acquire_stable_list();
215 void acquire_stable_list_fast_path();
216 void acquire_stable_list_nested_path();
217
218 void release_stable_list();
219
220 void verify_hazard_ptr_scanned();
221
222 public:
223 // Constructor that attaches the list onto a thread.
224 SafeThreadsListPtr(Thread *thread, bool acquire) :
225 _previous(NULL),
226 _thread(thread),
227 _list(NULL),
228 _has_ref_count(false),
229 _needs_release(false)
230 {
231 if (acquire) {
232 acquire_stable_list();
233 }
234 }
235
236 // Constructor that transfers ownership of the pointer.
237 SafeThreadsListPtr(SafeThreadsListPtr& other) :
238 _previous(other._previous),
239 _thread(other._thread),
240 _list(other._list),
241 _has_ref_count(other._has_ref_count),
242 _needs_release(other._needs_release)
243 {
244 other._needs_release = false;
245 }
246
247 ~SafeThreadsListPtr() {
248 if (_needs_release) {
249 release_stable_list();
250 }
251 }
252
253 ThreadsList* list() const { return _list; }
254 SafeThreadsListPtr* previous() const { return _previous; }
255 void print_on(outputStream* st);
256 };
257
258 // A helper to optionally set the hazard ptr in ourself. This helper can
259 // be used by ourself or by another thread. If the hazard ptr is set(),
260 // then the destructor will release it.
261 //
262 class ThreadsListSetter : public StackObj {
263 private:
264 SafeThreadsListPtr _list_ptr;
265
266 public:
267 ThreadsListSetter() : _list_ptr(Thread::current(), /* acquire */ false) {}
268 ThreadsList* list() { return _list_ptr.list(); }
269 void set() { _list_ptr.acquire_stable_list(); }
270 bool is_set() { return _list_ptr._needs_release; }
271 };
272
273 // This stack allocated ThreadsListHandle keeps all JavaThreads in the
274 // ThreadsList from being deleted until it is safe.
275 //
276 class ThreadsListHandle : public StackObj {
277 SafeThreadsListPtr _list_ptr;
278 elapsedTimer _timer; // Enabled via -XX:+EnableThreadSMRStatistics.
279
280 public:
281 ThreadsListHandle(Thread *self = Thread::current());
282 ~ThreadsListHandle();
283
284 ThreadsList *list() const {
285 return _list_ptr.list();
286 }
287
288 template <class T>
289 void threads_do(T *cl) const {
290 return list()->threads_do(cl);
291 }
292
293 bool cv_internal_thread_to_JavaThread(jobject jthread, JavaThread ** jt_pp, oop * thread_oop_p);
294
295 bool includes(JavaThread* p) {
296 return list()->includes(p);
297 }
298
299 uint length() const {
300 return list()->length();
301 }
302
303 JavaThread *thread_at(uint i) const {
304 return list()->thread_at(i);
305 }
306 };
307
308 // This stack allocated JavaThreadIterator is used to walk the
309 // specified ThreadsList using the following style:
310 //
311 // JavaThreadIterator jti(t_list);
312 // for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) {
313 // ...
314 // }
315 //
316 class JavaThreadIterator : public StackObj {
317 ThreadsList * _list;
318 uint _index;
319
320 public:
321 JavaThreadIterator(ThreadsList *list) : _list(list), _index(0) {
322 assert(list != NULL, "ThreadsList must not be NULL.");
323 }
324
325 JavaThread *first() {
326 _index = 0;
327 return _list->thread_at(_index);
328 }
329
330 uint length() const {
331 return _list->length();
332 }
333
334 ThreadsList *list() const {
335 return _list;
336 }
337
338 JavaThread *next() {
339 if (++_index >= length()) {
340 return NULL;
341 }
342 return _list->thread_at(_index);
343 }
344 };
345
346 // This stack allocated ThreadsListHandle and JavaThreadIterator combo
347 // is used to walk the ThreadsList in the included ThreadsListHandle
348 // using the following style:
349 //
350 // for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
351 // ...
352 // }
353 //
354 class JavaThreadIteratorWithHandle : public StackObj {
355 ThreadsListHandle _tlh;
356 uint _index;
357
358 public:
359 JavaThreadIteratorWithHandle() : _index(0) {}
360
361 uint length() const {
362 return _tlh.length();
363 }
364
365 ThreadsList *list() const {
366 return _tlh.list();
367 }
368
369 JavaThread *next() {
370 if (_index >= length()) {
371 return NULL;
372 }
373 return _tlh.list()->thread_at(_index++);
374 }
375
376 void rewind() {
377 _index = 0;
378 }
379 };
380
381 #endif // SHARE_RUNTIME_THREADSMR_HPP