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