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
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.inline.hpp"
31 #include "runtime/orderAccess.hpp"
32 #include "runtime/osThread.hpp"
33 #include "runtime/semaphore.inline.hpp"
34 #include "runtime/task.hpp"
35 #include "runtime/timerTrace.hpp"
36 #include "runtime/thread.hpp"
37 #include "runtime/vmThread.hpp"
38 #include "utilities/formatBuffer.hpp"
39 #include "utilities/preserveException.hpp"
40
41 class HandshakeOperation: public StackObj {
42 public:
43 virtual void do_handshake(JavaThread* thread) = 0;
44 };
45
46 class HandshakeThreadsOperation: public HandshakeOperation {
47 static Semaphore _done;
48 ThreadClosure* _thread_cl;
49
50 public:
51 HandshakeThreadsOperation(ThreadClosure* cl) : _thread_cl(cl) {}
52 void do_handshake(JavaThread* thread);
53 bool thread_has_completed() { return _done.trywait(); }
54
55 #ifdef ASSERT
56 void check_state() {
57 assert(!_done.trywait(), "Must be zero");
58 }
59 #endif
60 };
61
62 Semaphore HandshakeThreadsOperation::_done(0);
63
64 class VM_Handshake: public VM_Operation {
65 const jlong _handshake_timeout;
66 public:
67 bool evaluate_at_safepoint() const { return false; }
68
69 bool evaluate_concurrently() const { return false; }
70
71 protected:
72 HandshakeThreadsOperation* const _op;
73
74 VM_Handshake(HandshakeThreadsOperation* op) :
75 _handshake_timeout(TimeHelper::millis_to_counter(HandshakeTimeout)), _op(op) {}
76
77 void set_handshake(JavaThread* target) {
78 target->set_handshake_operation(_op);
79 }
80
81 // This method returns true for threads completed their operation
82 // and true for threads canceled their operation.
83 // A cancellation can happen if the thread is exiting.
84 bool poll_for_completed_thread() { return _op->thread_has_completed(); }
85
86 bool handshake_has_timed_out(jlong start_time);
87 static void handle_timeout();
88 };
89
90 bool VM_Handshake::handshake_has_timed_out(jlong start_time) {
91 // Check if handshake operation has timed out
92 if (_handshake_timeout > 0) {
93 return os::elapsed_counter() >= (start_time + _handshake_timeout);
94 }
95 return false;
96 }
97
98 void VM_Handshake::handle_timeout() {
99 LogStreamHandle(Warning, handshake) log_stream;
100 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
101 if (thr->has_handshake()) {
102 log_stream.print("Thread " PTR_FORMAT " has not cleared its handshake op", p2i(thr));
103 thr->print_thread_state_on(&log_stream);
104 }
105 }
106 log_stream.flush();
107 fatal("Handshake operation timed out");
108 }
109
110 class VM_HandshakeOneThread: public VM_Handshake {
111 JavaThread* _target;
112 bool _thread_alive;
113 public:
114 VM_HandshakeOneThread(HandshakeThreadsOperation* op, JavaThread* target) :
115 VM_Handshake(op), _target(target), _thread_alive(false) {}
116
117 void doit() {
118 DEBUG_ONLY(_op->check_state();)
119 TraceTime timer("Performing single-target operation (vmoperation doit)", TRACETIME_LOG(Info, handshake));
120
121 ThreadsListHandle tlh;
122 if (tlh.includes(_target)) {
123 set_handshake(_target);
124 _thread_alive = true;
125 } else {
126 return;
127 }
128
129 if (!UseMembar) {
130 os::serialize_thread_states();
131 }
132
133 log_trace(handshake)("Thread signaled, begin processing by VMThtread");
134 jlong start_time = os::elapsed_counter();
135 do {
136 if (handshake_has_timed_out(start_time)) {
137 handle_timeout();
138 }
139
140 // We need to re-think this with SMR ThreadsList.
141 // There is an assumption in the code that the Threads_lock should be
142 // locked during certain phases.
143 {
144 MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
145 _target->handshake_process_by_vmthread();
146 }
147 } while (!poll_for_completed_thread());
148 DEBUG_ONLY(_op->check_state();)
149 }
150
151 VMOp_Type type() const { return VMOp_HandshakeOneThread; }
152
153 bool thread_alive() const { return _thread_alive; }
154 };
155
156 class VM_HandshakeAllThreads: public VM_Handshake {
157 public:
158 VM_HandshakeAllThreads(HandshakeThreadsOperation* op) : VM_Handshake(op) {}
159
160 void doit() {
161 DEBUG_ONLY(_op->check_state();)
162 TraceTime timer("Performing operation (vmoperation doit)", TRACETIME_LOG(Info, handshake));
163
164 JavaThreadIteratorWithHandle jtiwh;
165 int number_of_threads_issued = 0;
166 for ( ; JavaThread *thr = jtiwh.next(); ) {
167 set_handshake(thr);
168 number_of_threads_issued++;
169 }
170
171 if (number_of_threads_issued < 1) {
172 log_debug(handshake)("No threads to handshake.");
173 return;
174 }
175
176 if (!UseMembar) {
177 os::serialize_thread_states();
178 }
179
180 log_debug(handshake)("Threads signaled, begin processing blocked threads by VMThtread");
181 const jlong start_time = os::elapsed_counter();
182 int number_of_threads_completed = 0;
183 do {
184 // Check if handshake operation has timed out
185 if (handshake_has_timed_out(start_time)) {
186 handle_timeout();
187 }
188
189 // Have VM thread perform the handshake operation for blocked threads.
190 // Observing a blocked state may of course be transient but the processing is guarded
191 // by semaphores and we optimistically begin by working on the blocked threads
192 {
193 // We need to re-think this with SMR ThreadsList.
194 // There is an assumption in the code that the Threads_lock should
195 // be locked during certain phases.
196 jtiwh.rewind();
197 MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
198 for ( ; JavaThread *thr = jtiwh.next(); ) {
199 // A new thread on the ThreadsList will not have an operation,
200 // hence it is skipped in handshake_process_by_vmthread.
201 thr->handshake_process_by_vmthread();
202 }
203 }
204
205 while (poll_for_completed_thread()) {
206 // Includes canceled operations by exiting threads.
207 number_of_threads_completed++;
208 }
209
210 } while (number_of_threads_issued > number_of_threads_completed);
211 assert(number_of_threads_issued == number_of_threads_completed, "Must be the same");
212 DEBUG_ONLY(_op->check_state();)
213 }
214
215 VMOp_Type type() const { return VMOp_HandshakeAllThreads; }
216 };
217
218 class VM_HandshakeFallbackOperation : public VM_Operation {
219 ThreadClosure* _thread_cl;
220 Thread* _target_thread;
221 bool _all_threads;
222 bool _thread_alive;
223 public:
224 VM_HandshakeFallbackOperation(ThreadClosure* cl) :
225 _thread_cl(cl), _target_thread(NULL), _all_threads(true), _thread_alive(true) {}
226 VM_HandshakeFallbackOperation(ThreadClosure* cl, Thread* target) :
227 _thread_cl(cl), _target_thread(target), _all_threads(false), _thread_alive(false) {}
228
229 void doit() {
230 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
231 if (_all_threads || t == _target_thread) {
232 if (t == _target_thread) {
233 _thread_alive = true;
234 }
235 _thread_cl->do_thread(t);
236 }
237 }
238 }
239
240 VMOp_Type type() const { return VMOp_HandshakeFallback; }
241 bool thread_alive() const { return _thread_alive; }
242 };
243
244 void HandshakeThreadsOperation::do_handshake(JavaThread* thread) {
245 ResourceMark rm;
246 FormatBufferResource message("Operation for thread " PTR_FORMAT ", is_vm_thread: %s",
247 p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread()));
248 TraceTime timer(message, TRACETIME_LOG(Debug, handshake, task));
249
250 // Only actually execute the operation for non terminated threads.
251 if (!thread->is_terminated()) {
252 _thread_cl->do_thread(thread);
253 }
254
255 // Use the semaphore to inform the VM thread that we have completed the operation
256 _done.signal();
257 }
258
259 void Handshake::execute(ThreadClosure* thread_cl) {
260 if (ThreadLocalHandshakes) {
261 HandshakeThreadsOperation cto(thread_cl);
262 VM_HandshakeAllThreads handshake(&cto);
263 VMThread::execute(&handshake);
264 } else {
265 VM_HandshakeFallbackOperation op(thread_cl);
266 VMThread::execute(&op);
267 }
268 }
269
270 bool Handshake::execute(ThreadClosure* thread_cl, JavaThread* target) {
271 if (ThreadLocalHandshakes) {
272 HandshakeThreadsOperation cto(thread_cl);
273 VM_HandshakeOneThread handshake(&cto, target);
274 VMThread::execute(&handshake);
275 return handshake.thread_alive();
276 } else {
277 VM_HandshakeFallbackOperation op(thread_cl, target);
278 VMThread::execute(&op);
279 return op.thread_alive();
280 }
281 }
282
283 HandshakeState::HandshakeState() : _operation(NULL), _semaphore(1), _thread_in_process_handshake(false) {}
284
285 void HandshakeState::set_operation(JavaThread* target, HandshakeOperation* op) {
286 _operation = op;
287 SafepointMechanism::arm_local_poll_release(target);
288 }
289
290 void HandshakeState::clear_handshake(JavaThread* target) {
291 _operation = NULL;
292 SafepointMechanism::disarm_local_poll_release(target);
293 }
294
295 void HandshakeState::process_self_inner(JavaThread* thread) {
296 assert(Thread::current() == thread, "should call from thread");
297 assert(!thread->is_terminated(), "should not be a terminated thread");
298
299 CautiouslyPreserveExceptionMark pem(thread);
300 ThreadInVMForHandshake tivm(thread);
301 if (!_semaphore.trywait()) {
302 _semaphore.wait_with_safepoint_check(thread);
303 }
304 HandshakeOperation* op = OrderAccess::load_acquire(&_operation);
305 if (op != NULL) {
306 // Disarm before execute the operation
307 clear_handshake(thread);
308 op->do_handshake(thread);
309 }
310 _semaphore.signal();
311 }
312
313 bool HandshakeState::vmthread_can_process_handshake(JavaThread* target) {
314 // SafepointSynchronize::safepoint_safe() does not consider an externally
315 // suspended thread to be safe. However, this function must be called with
316 // the Threads_lock held so an externally suspended thread cannot be
317 // resumed thus it is safe.
318 assert(Threads_lock->owned_by_self(), "Not holding Threads_lock.");
319 return SafepointSynchronize::safepoint_safe(target, target->thread_state()) ||
320 target->is_ext_suspended() || target->is_terminated();
321 }
322
323 static bool possibly_vmthread_can_process_handshake(JavaThread* target) {
324 // An externally suspended thread cannot be resumed while the
325 // Threads_lock is held so it is safe.
326 // Note that this method is allowed to produce false positives.
327 assert(Threads_lock->owned_by_self(), "Not holding Threads_lock.");
328 if (target->is_ext_suspended()) {
329 return true;
330 }
331 if (target->is_terminated()) {
332 return true;
333 }
334 switch (target->thread_state()) {
335 case _thread_in_native:
336 // native threads are safe if they have no java stack or have walkable stack
337 return !target->has_last_Java_frame() || target->frame_anchor()->walkable();
338
339 case _thread_blocked:
340 return true;
341
342 default:
343 return false;
344 }
345 }
346
347 bool HandshakeState::claim_handshake_for_vmthread() {
348 if (!_semaphore.trywait()) {
349 return false;
350 }
351 if (has_operation()) {
352 return true;
353 }
354 _semaphore.signal();
355 return false;
356 }
357
358 void HandshakeState::process_by_vmthread(JavaThread* target) {
359 assert(Thread::current()->is_VM_thread(), "should call from vm thread");
360 // Threads_lock must be held here, but that is assert()ed in
361 // possibly_vmthread_can_process_handshake().
362
363 if (!has_operation()) {
364 // JT has already cleared its handshake
365 return;
366 }
367
368 if (!possibly_vmthread_can_process_handshake(target)) {
369 // JT is observed in an unsafe state, it must notice the handshake itself
370 return;
371 }
372
373 // Claim the semaphore if there still an operation to be executed.
374 if (!claim_handshake_for_vmthread()) {
375 return;
376 }
377
378 // If we own the semaphore at this point and while owning the semaphore
379 // can observe a safe state the thread cannot possibly continue without
380 // getting caught by the semaphore.
381 if (vmthread_can_process_handshake(target)) {
382 guarantee(!_semaphore.trywait(), "we should already own the semaphore");
383 _operation->do_handshake(target);
384 // Disarm after VM thread have executed the operation.
385 clear_handshake(target);
386 // Release the thread
387 }
388
389 _semaphore.signal();
390 }