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