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