1 /*
2 * Copyright (c) 2017, 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 #include "precompiled.hpp"
26 #include "logging/log.hpp"
27 #include "logging/logStream.hpp"
28 #include "memory/resourceArea.hpp"
29 #include "runtime/handshake.hpp"
30 #include "runtime/interfaceSupport.hpp"
31 #include "runtime/osThread.hpp"
32 #include "runtime/semaphore.hpp"
33 #include "runtime/task.hpp"
34 #include "runtime/timerTrace.hpp"
35 #include "runtime/thread.hpp"
36 #include "runtime/vmThread.hpp"
37 #include "utilities/formatBuffer.hpp"
38 #include "utilities/preserveException.hpp"
39
40 class HandshakeOperation: public StackObj {
41 public:
42 virtual void do_handshake(JavaThread* thread) = 0;
43 virtual void cancel_handshake(JavaThread* thread) = 0;
44 };
45
46 class HandshakeThreadsOperation: public HandshakeOperation {
47 Semaphore _done;
48 ThreadClosure* _thread_cl;
49
50 public:
51 HandshakeThreadsOperation(ThreadClosure* cl) : _done(0), _thread_cl(cl) {}
52 void do_handshake(JavaThread* thread);
53 void cancel_handshake(JavaThread* thread) { _done.signal(); };
54
55 bool thread_has_completed() { return _done.trywait(); }
56 };
57
58 class VM_Handshake: public VM_Operation {
59 HandshakeThreadsOperation* const _op;
60 const jlong _handshake_timeout;
61 public:
62 bool evaluate_at_safepoint() const { return false; }
63
64 bool evaluate_concurrently() const { return false; }
65
66 protected:
67
68 VM_Handshake(HandshakeThreadsOperation* op) :
69 _op(op),
70 _handshake_timeout(TimeHelper::millis_to_counter(HandshakeTimeout)) {}
71
72 void set_handshake(JavaThread* target) {
73 target->set_handshake_operation(_op);
74 }
75
76 // This method returns true for threads completed their operation
77 // and true for threads canceled their operation.
78 // A cancellation can happen if the thread is exiting.
79 bool poll_for_completed_thread() { return _op->thread_has_completed(); }
80
81 bool handshake_has_timed_out(jlong start_time);
82 static void handle_timeout();
83 };
84
85 bool VM_Handshake::handshake_has_timed_out(jlong start_time) {
86 // Check if handshake operation has timed out
87 if (_handshake_timeout > 0) {
88 return os::elapsed_counter() >= (start_time + _handshake_timeout);
89 }
90 return false;
91 }
92
93 void VM_Handshake::handle_timeout() {
94 LogStreamHandle(Warning, handshake) log_stream;
95 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
96 if (thr->has_handshake()) {
97 log_stream.print("Thread " PTR_FORMAT " has not cleared its handshake op", p2i(thr));
98 thr->print_thread_state_on(&log_stream);
99 }
100 }
101 log_stream.flush();
102 fatal("Handshake operation timed out");
103 }
104
105
106 class VM_HandshakeOneThread: public VM_Handshake {
107 JavaThread* _target;
108 bool _thread_alive;
109 public:
110 VM_HandshakeOneThread(HandshakeThreadsOperation* op, JavaThread* target) :
111 VM_Handshake(op), _target(target), _thread_alive(false) {}
112
113 void doit() {
114 TraceTime timer("Performing single-target operation (vmoperation doit)", TRACETIME_LOG(Info, handshake));
115
116 {
117 ThreadsListHandle tlh;
118 if (tlh.includes(_target)) {
119 set_handshake(_target);
120 _thread_alive = true;
121 }
122 }
123
124 if (!_thread_alive) {
125 return;
126 }
127
128 if (!UseMembar) {
129 os::serialize_thread_states();
130 }
131
132 log_trace(handshake)("Thread signaled, begin processing by VMThtread");
133 jlong start_time = os::elapsed_counter();
134 do {
135 if (handshake_has_timed_out(start_time)) {
136 handle_timeout();
137 }
138
139 // We need to re-think this with SMR ThreadsList.
140 // There is an assumption in the code that the Threads_lock should be
141 // locked during certain phases.
142 MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
143 ThreadsListHandle tlh;
144 if (tlh.includes(_target)) {
145 // Warning _target's address might be re-used.
146 // handshake_process_by_vmthread will check the semaphore for us again.
147 // Since we can't have more then one handshake in flight a reuse of
148 // _target's address should be okay since the new thread will not have
149 // an operation.
150 _target->handshake_process_by_vmthread();
151 } else {
152 // We can't warn here since the thread does cancel_handshake after
153 // it has been removed from the ThreadsList. So we should just keep
154 // looping here until while below returns false. If we have a bug,
155 // then we hang here, which is good for debugging.
156 }
157 } while (!poll_for_completed_thread());
158 }
159
160 VMOp_Type type() const { return VMOp_HandshakeOneThread; }
161
162 bool thread_alive() const { return _thread_alive; }
163 };
164
165 class VM_HandshakeAllThreads: public VM_Handshake {
166 public:
167 VM_HandshakeAllThreads(HandshakeThreadsOperation* op) : VM_Handshake(op) {}
168
169 void doit() {
170 TraceTime timer("Performing operation (vmoperation doit)", TRACETIME_LOG(Info, handshake));
171
172 int number_of_threads_issued = 0;
173 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
174 set_handshake(thr);
175 number_of_threads_issued++;
176 }
177
178 if (number_of_threads_issued < 1) {
179 log_debug(handshake)("No threads to handshake.");
180 return;
181 }
182
183 if (!UseMembar) {
184 os::serialize_thread_states();
185 }
186
187 log_debug(handshake)("Threads signaled, begin processing blocked threads by VMThtread");
188 const jlong start_time = os::elapsed_counter();
189 int number_of_threads_completed = 0;
190 do {
191 // Check if handshake operation has timed out
192 if (handshake_has_timed_out(start_time)) {
193 handle_timeout();
194 }
195
196 // Have VM thread perform the handshake operation for blocked threads.
197 // Observing a blocked state may of course be transient but the processing is guarded
198 // by semaphores and we optimistically begin by working on the blocked threads
199 {
200 // We need to re-think this with SMR ThreadsList.
201 // There is an assumption in the code that the Threads_lock should
202 // be locked during certain phases.
203 MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
204 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
205 // A new thread on the ThreadsList will not have an operation,
206 // hence it is skipped in handshake_process_by_vmthread.
207 thr->handshake_process_by_vmthread();
208 }
209 }
210
211 while (poll_for_completed_thread()) {
212 // Includes canceled operations by exiting threads.
213 number_of_threads_completed++;
214 }
215
216 } while (number_of_threads_issued != number_of_threads_completed);
217 }
218
219 VMOp_Type type() const { return VMOp_HandshakeAllThreads; }
220 };
221
222 class VM_HandshakeFallbackOperation : public VM_Operation {
223 ThreadClosure* _thread_cl;
224 Thread* _target_thread;
225 bool _all_threads;
226 bool _thread_alive;
227 public:
228 VM_HandshakeFallbackOperation(ThreadClosure* cl) :
229 _thread_cl(cl), _target_thread(NULL), _all_threads(true), _thread_alive(true) {}
230 VM_HandshakeFallbackOperation(ThreadClosure* cl, Thread* target) :
231 _thread_cl(cl), _target_thread(target), _all_threads(false), _thread_alive(false) {}
232
233 void doit() {
234 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
235 if (_all_threads || t == _target_thread) {
236 if (t == _target_thread) {
237 _thread_alive = true;
238 }
239 _thread_cl->do_thread(t);
240 }
241 }
242 }
243
244 VMOp_Type type() const { return VMOp_HandshakeFallback; }
245 bool thread_alive() const { return _thread_alive; }
246 };
247
248 #undef ALL_JAVA_THREADS
249
250 void HandshakeThreadsOperation::do_handshake(JavaThread* thread) {
251 ResourceMark rm;
252 FormatBufferResource message("Operation for thread " PTR_FORMAT ", is_vm_thread: %s",
253 p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread()));
254 TraceTime timer(message, TRACETIME_LOG(Debug, handshake, task));
255 _thread_cl->do_thread(thread);
256
257 // Use the semaphore to inform the VM thread that we have completed the operation
258 _done.signal();
259 }
260
261 void Handshake::execute(ThreadClosure* thread_cl) {
262 if (ThreadLocalHandshakes) {
263 HandshakeThreadsOperation cto(thread_cl);
264 VM_HandshakeAllThreads handshake(&cto);
265 VMThread::execute(&handshake);
266 } else {
267 VM_HandshakeFallbackOperation op(thread_cl);
268 VMThread::execute(&op);
269 }
270 }
271
272 bool Handshake::execute(ThreadClosure* thread_cl, JavaThread* target) {
273 if (ThreadLocalHandshakes) {
274 HandshakeThreadsOperation cto(thread_cl);
275 VM_HandshakeOneThread handshake(&cto, target);
276 VMThread::execute(&handshake);
277 return handshake.thread_alive();
278 } else {
279 VM_HandshakeFallbackOperation op(thread_cl, target);
280 VMThread::execute(&op);
281 return op.thread_alive();
282 }
283 }
284
285 HandshakeState::HandshakeState() : _operation(NULL), _semaphore(1), _vmthread_holds_semaphore(false), _thread_in_process_handshake(false) {}
286
287 void HandshakeState::set_operation(JavaThread* target, HandshakeOperation* op) {
288 _operation = op;
289 SafepointMechanism::arm_local_poll(target);
290 }
291
292 void HandshakeState::clear_handshake(JavaThread* target) {
293 _operation = NULL;
294 SafepointMechanism::disarm_local_poll(target);
295 }
296
297 void HandshakeState::process_self_inner(JavaThread* thread) {
298 assert(Thread::current() == thread, "should call from thread");
299 CautiouslyPreserveExceptionMark pem(thread);
300 ThreadInVMForHandshake tivm(thread);
301 if (!_semaphore.trywait()) {
302 ThreadBlockInVM tbivm(thread);
303 _semaphore.wait();
304 }
305 if (has_operation()) {
306 HandshakeOperation* op = _operation;
307 clear_handshake(thread);
308 if (op != NULL) {
309 op->do_handshake(thread);
310 }
311 }
312 _semaphore.signal();
313 }
314
315 void HandshakeState::cancel_inner(JavaThread* thread) {
316 assert(Thread::current() == thread, "should call from thread");
317 assert(thread->thread_state() == _thread_in_vm, "must be in vm state");
318 #ifdef DEBUG
319 {
320 ThreadsListHandle tlh;
321 assert(!tlh.includes(_target), "java thread must not be on threads list");
322 }
323 #endif
324 HandshakeOperation* op = _operation;
325 clear_handshake(thread);
326 if (op != NULL) {
327 op->cancel_handshake(thread);
328 }
329 }
330
331 bool HandshakeState::vmthread_can_process_handshake(JavaThread* target) {
332 return SafepointSynchronize::safepoint_safe(target, target->thread_state());
333 }
334
335 bool HandshakeState::claim_handshake_for_vmthread() {
336 if (_semaphore.trywait()) {
337 if (has_operation()) {
338 _vmthread_holds_semaphore = true;
339 } else {
340 _semaphore.signal();
341 }
342 }
343 return _vmthread_holds_semaphore;
344 }
345
346 void HandshakeState::process_by_vmthread(JavaThread* target) {
347 assert(Thread::current()->is_VM_thread(), "should call from vm thread");
348
349 if (!has_operation()) {
350 // JT has already cleared its handshake
351 return;
352 }
353
354 if (!vmthread_can_process_handshake(target)) {
355 // JT is observed in an unsafe state, it must notice the handshake itself
356 return;
357 }
358
359 // If we own the semaphore at this point and while owning the semaphore
360 // can observe a safe state the thread cannot possibly continue without
361 // getting caught by the semaphore.
362 if (claim_handshake_for_vmthread() && vmthread_can_process_handshake(target)) {
363 guarantee(!_semaphore.trywait(), "we should already own the semaphore");
364
365 _operation->do_handshake(target);
366 clear_handshake(target);
367 _vmthread_holds_semaphore = false;
368 // Release the thread
369 _semaphore.signal();
370 }
371 }