1 /*
2 * Copyright (c) 2017, 2018, 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
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23 */
24
25 #ifndef SHARE_VM_RUNTIME_THREADSMR_HPP
26 #define SHARE_VM_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 SafeThreadsListPtr; // for _nested_thread_list_max, delete_notify(), release_stable_list_wake_up() access
90
91 // The coordination between ThreadsSMRSupport::release_stable_list() and
92 // ThreadsSMRSupport::smr_delete() uses the delete_lock in order to
93 // reduce the traffic on the Threads_lock.
94 static Monitor* _delete_lock;
95 // The '_cnt', '_max' and '_times" fields are enabled via
96 // -XX:+EnableThreadSMRStatistics (see thread.cpp for a
97 // description about each field):
98 static uint _delete_lock_wait_cnt;
99 static uint _delete_lock_wait_max;
100 // The delete_notify flag is used for proper double-check
101 // locking in order to reduce the traffic on the system wide
102 // Thread-SMR delete_lock.
103 static volatile uint _delete_notify;
104 static volatile uint _deleted_thread_cnt;
105 static volatile uint _deleted_thread_time_max;
106 static volatile uint _deleted_thread_times;
107 static ThreadsList* volatile _java_thread_list;
108 static uint64_t _java_thread_list_alloc_cnt;
109 static uint64_t _java_thread_list_free_cnt;
110 static uint _java_thread_list_max;
111 static uint _nested_thread_list_max;
112 static volatile uint _tlh_cnt;
113 static volatile uint _tlh_time_max;
114 static volatile uint _tlh_times;
115 static ThreadsList* _to_delete_list;
116 static uint _to_delete_list_cnt;
117 static uint _to_delete_list_max;
118
119 static ThreadsList *acquire_stable_list_fast_path(Thread *self);
120 static ThreadsList *acquire_stable_list_nested_path(Thread *self);
121 static void add_deleted_thread_times(uint add_value);
122 static void add_tlh_times(uint add_value);
123 static void clear_delete_notify();
124 static Monitor* delete_lock() { return _delete_lock; }
125 static bool delete_notify();
126 static void free_list(ThreadsList* threads);
127 static void inc_deleted_thread_cnt();
128 static void inc_java_thread_list_alloc_cnt();
129 static void inc_tlh_cnt();
130 static bool is_a_protected_JavaThread(JavaThread *thread);
131 static void release_stable_list_wake_up(bool is_nested);
132 static void set_delete_notify();
133 static void threads_do(ThreadClosure *tc);
134 static void threads_do(ThreadClosure *tc, ThreadsList *list);
135 static void update_deleted_thread_time_max(uint new_value);
136 static void update_java_thread_list_max(uint new_value);
137 static void update_tlh_time_max(uint new_value);
138 static void verify_hazard_ptr_scanned(Thread *self, ThreadsList *threads);
139 static ThreadsList* xchg_java_thread_list(ThreadsList* new_list);
140
141 public:
142 static void add_thread(JavaThread *thread);
143 static ThreadsList* get_java_thread_list();
144 static bool is_a_protected_JavaThread_with_lock(JavaThread *thread);
145 static void remove_thread(JavaThread *thread);
146 static void smr_delete(JavaThread *thread);
147 static void update_tlh_stats(uint millis);
148
149 // Logging and printing support:
150 static void log_statistics();
151 static void print_info_elements_on(outputStream* st, ThreadsList* t_list);
152 static void print_info_on(outputStream* st);
153 static void print_info_on(const Thread* thread, outputStream* st);
154 };
155
156 // A fast list of JavaThreads.
157 //
158 class ThreadsList : public CHeapObj<mtThread> {
159 friend class SafeThreadsListPtr; // for {dec,inc}_nested_handle_cnt() access
160 friend class ThreadsSMRSupport; // for _nested_handle_cnt, {add,remove}_thread(), {,set_}next_list() access
161
162 const uint _length;
163 ThreadsList* _next_list;
164 JavaThread *const *const _threads;
165 volatile intx _nested_handle_cnt;
166
167 template <class T>
168 void threads_do_dispatch(T *cl, JavaThread *const thread) const;
169
170 ThreadsList *next_list() const { return _next_list; }
171 void set_next_list(ThreadsList *list) { _next_list = list; }
172
173 void inc_nested_handle_cnt();
174 void dec_nested_handle_cnt();
175
176 static ThreadsList* add_thread(ThreadsList* list, JavaThread* java_thread);
177 static ThreadsList* remove_thread(ThreadsList* list, JavaThread* java_thread);
178
179 public:
180 ThreadsList(int entries);
181 ~ThreadsList();
182
183 template <class T>
184 void threads_do(T *cl) const;
185
186 uint length() const { return _length; }
187
188 JavaThread *const thread_at(uint i) const { return _threads[i]; }
189
190 JavaThread *const *threads() const { return _threads; }
191
192 // Returns -1 if target is not found.
193 int find_index_of_JavaThread(JavaThread* target);
194 JavaThread* find_JavaThread_from_java_tid(jlong java_tid) const;
195 bool includes(const JavaThread * const p) const;
196 };
197
198 // An abstract safe ptr to a ThreadsList comprising either a stable hazard ptr
199 // for leaves, or a retained reference count for nested uses. The user of this
200 // API does not need to know which mechanism is providing the safety.
201 class SafeThreadsListPtr {
202 friend class ThreadsListSetter;
203
204 SafeThreadsListPtr* _previous;
205 Thread* _thread;
206 ThreadsList* _list;
207 bool _has_ref_count;
208 bool _needs_release;
209
210 void acquire_stable_list();
211 void acquire_stable_list_fast_path();
212 void acquire_stable_list_nested_path();
213
214 void release_stable_list();
215
216 void verify_hazard_ptr_scanned();
217
218 public:
219 // Constructor that attaches the list onto a thread.
220 SafeThreadsListPtr(Thread *thread, bool acquire) :
221 _previous(NULL),
222 _thread(thread),
223 _list(NULL),
224 _has_ref_count(false),
225 _needs_release(false)
226 {
227 if (acquire) {
228 acquire_stable_list();
229 }
230 }
231
232 // Constructor that transfers ownership of the pointer.
233 SafeThreadsListPtr(SafeThreadsListPtr& other) :
234 _previous(other._previous),
235 _thread(other._thread),
236 _list(other._list),
237 _has_ref_count(other._has_ref_count),
238 _needs_release(other._needs_release)
239 {
240 other._needs_release = false;
241 }
242
243 ~SafeThreadsListPtr() {
244 if (_needs_release) {
245 release_stable_list();
246 }
247 }
248
249 ThreadsList* list() const { return _list; }
250 SafeThreadsListPtr* previous() const { return _previous; }
251 void print_on(outputStream* st);
252 };
253
254 // A helper to optionally set the hazard ptr in ourself. This helper can
255 // be used by ourself or by another thread. If the hazard ptr is set(),
256 // then the destructor will release it.
257 //
258 class ThreadsListSetter : public StackObj {
259 private:
260 SafeThreadsListPtr _list_ptr;
261
262 public:
263 ThreadsListSetter() : _list_ptr(Thread::current(), /* acquire */ false) {}
264 ThreadsList* list() { return _list_ptr.list(); }
265 void set() { _list_ptr.acquire_stable_list(); }
266 bool is_set() { return _list_ptr._needs_release; }
267 };
268
269 // This stack allocated ThreadsListHandle keeps all JavaThreads in the
270 // ThreadsList from being deleted until it is safe.
271 //
272 class ThreadsListHandle : public StackObj {
273 SafeThreadsListPtr _list_ptr;
274 elapsedTimer _timer; // Enabled via -XX:+EnableThreadSMRStatistics.
275
276 public:
277 ThreadsListHandle(Thread *self = Thread::current());
278 ~ThreadsListHandle();
279
280 ThreadsList *list() const {
281 return _list_ptr.list();
282 }
283
284 template <class T>
285 void threads_do(T *cl) const {
286 return list()->threads_do(cl);
287 }
288
289 bool cv_internal_thread_to_JavaThread(jobject jthread, JavaThread ** jt_pp, oop * thread_oop_p);
290
291 bool includes(JavaThread* p) {
292 return list()->includes(p);
293 }
294
295 uint length() const {
296 return list()->length();
297 }
298 };
299
300 // This stack allocated JavaThreadIterator is used to walk the
301 // specified ThreadsList using the following style:
302 //
303 // JavaThreadIterator jti(t_list);
304 // for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) {
305 // ...
306 // }
307 //
308 class JavaThreadIterator : public StackObj {
309 ThreadsList * _list;
310 uint _index;
311
312 public:
313 JavaThreadIterator(ThreadsList *list) : _list(list), _index(0) {
314 assert(list != NULL, "ThreadsList must not be NULL.");
315 }
316
317 JavaThread *first() {
318 _index = 0;
319 return _list->thread_at(_index);
320 }
321
322 uint length() const {
323 return _list->length();
324 }
325
326 ThreadsList *list() const {
327 return _list;
328 }
329
330 JavaThread *next() {
331 if (++_index >= length()) {
332 return NULL;
333 }
334 return _list->thread_at(_index);
335 }
336 };
337
338 // This stack allocated ThreadsListHandle and JavaThreadIterator combo
339 // is used to walk the ThreadsList in the included ThreadsListHandle
340 // using the following style:
341 //
342 // for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
343 // ...
344 // }
345 //
346 class JavaThreadIteratorWithHandle : public StackObj {
347 ThreadsListHandle _tlh;
348 uint _index;
349
350 public:
351 JavaThreadIteratorWithHandle() : _index(0) {}
352
353 uint length() const {
354 return _tlh.length();
355 }
356
357 ThreadsList *list() const {
358 return _tlh.list();
359 }
360
361 JavaThread *next() {
362 if (_index >= length()) {
363 return NULL;
364 }
365 return _tlh.list()->thread_at(_index++);
366 }
367
368 void rewind() {
369 _index = 0;
370 }
371 };
372
373 #endif // SHARE_VM_RUNTIME_THREADSMR_HPP