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/atomic.hpp"
30 #include "runtime/handshake.hpp"
31 #include "runtime/interfaceSupport.inline.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 class HandshakeOperation: public StackObj {
41 public:
42 virtual void do_handshake(JavaThread* thread) = 0;
43 };
44
45 class HandshakeThreadsOperation: public HandshakeOperation {
46 static Semaphore _done;
47 HandshakeClosure* _handshake_cl;
48 bool _executed;
49 public:
50 HandshakeThreadsOperation(HandshakeClosure* cl) : _handshake_cl(cl), _executed(false) {}
51 void do_handshake(JavaThread* thread);
52 bool thread_has_completed() { return _done.trywait(); }
53 bool executed() const { return _executed; }
54 const char* name() { return _handshake_cl->name(); }
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 bool evaluate_at_safepoint() const { return false; }
69
70 bool evaluate_concurrently() const { return false; }
71
72 protected:
73 HandshakeThreadsOperation* const _op;
74
75 VM_Handshake(HandshakeThreadsOperation* op) :
76 _handshake_timeout(TimeHelper::millis_to_counter(HandshakeTimeout)), _op(op) {}
77
78 void set_handshake(JavaThread* target) {
79 target->set_handshake_operation(_op);
80 }
81
82 // This method returns true for threads completed their operation
83 // and true for threads canceled their operation.
84 // A cancellation can happen if the thread is exiting.
85 bool poll_for_completed_thread() { return _op->thread_has_completed(); }
86
87 bool handshake_has_timed_out(jlong start_time);
88 static void handle_timeout();
89 };
90
91 bool VM_Handshake::handshake_has_timed_out(jlong start_time) {
92 // Check if handshake operation has timed out
93 if (_handshake_timeout > 0) {
94 return os::elapsed_counter() >= (start_time + _handshake_timeout);
95 }
96 return false;
97 }
98
99 void VM_Handshake::handle_timeout() {
100 LogStreamHandle(Warning, handshake) log_stream;
101 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
102 if (thr->has_handshake()) {
103 log_stream.print("Thread " PTR_FORMAT " has not cleared its handshake op", p2i(thr));
104 thr->print_thread_state_on(&log_stream);
105 }
106 }
107 log_stream.flush();
108 fatal("Handshake operation timed out");
109 }
110
111 static void log_handshake_info(jlong start_time_ns, const char* name, int targets, int vmt_executed, const char* extra = NULL) {
112 if (start_time_ns != 0) {
113 jlong completion_time = os::javaTimeNanos() - start_time_ns;
114 log_info(handshake)("Handshake \"%s\", Targeted threads: %d, Executed by targeted threads: %d, Total completion time: " JLONG_FORMAT " ns%s%s",
115 name, targets,
116 targets - vmt_executed,
117 completion_time,
118 extra != NULL ? ", " : "",
119 extra != NULL ? extra : "");
120 }
121 }
122
123 class VM_HandshakeOneThread: public VM_Handshake {
124 JavaThread* _target;
125 public:
126 VM_HandshakeOneThread(HandshakeThreadsOperation* op, JavaThread* target) :
127 VM_Handshake(op), _target(target) {}
128
129 void doit() {
130 DEBUG_ONLY(_op->check_state();)
131
132 jlong start_time_ns = 0;
133 if (log_is_enabled(Info, handshake)) {
134 start_time_ns = os::javaTimeNanos();
135 }
136
137 ThreadsListHandle tlh;
138 if (tlh.includes(_target)) {
139 set_handshake(_target);
140 } else {
141 log_handshake_info(start_time_ns, _op->name(), 0, 0, "(thread dead)");
142 return;
143 }
144
145 log_trace(handshake)("JavaThread " INTPTR_FORMAT " signaled, begin attempt to process by VMThtread", p2i(_target));
146 jlong timeout_start_time = os::elapsed_counter();
147 bool by_vm_thread = false;
148 do {
149 if (handshake_has_timed_out(timeout_start_time)) {
150 handle_timeout();
151 }
152
153 // We need to re-think this with SMR ThreadsList.
154 // There is an assumption in the code that the Threads_lock should be
155 // locked during certain phases.
156 {
157 MutexLocker ml(Threads_lock);
158 by_vm_thread = _target->handshake_try_process_by_vmThread();
159 }
160 } while (!poll_for_completed_thread());
161 DEBUG_ONLY(_op->check_state();)
162 log_handshake_info(start_time_ns, _op->name(), 1, by_vm_thread ? 1 : 0);
163 }
164
165 VMOp_Type type() const { return VMOp_HandshakeOneThread; }
166
167 bool executed() const { return _op->executed(); }
168 };
169
170 class VM_HandshakeAllThreads: public VM_Handshake {
171 public:
172 VM_HandshakeAllThreads(HandshakeThreadsOperation* op) : VM_Handshake(op) {}
173
174 void doit() {
175 DEBUG_ONLY(_op->check_state();)
176
177 jlong start_time_ns = 0;
178 if (log_is_enabled(Info, handshake)) {
179 start_time_ns = os::javaTimeNanos();
180 }
181 int handshake_executed_by_vm_thread = 0;
182
183 JavaThreadIteratorWithHandle jtiwh;
184 int number_of_threads_issued = 0;
185 for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
186 set_handshake(thr);
187 number_of_threads_issued++;
188 }
189
190 if (number_of_threads_issued < 1) {
191 log_handshake_info(start_time_ns, _op->name(), 0, 0);
192 return;
193 }
194
195 log_trace(handshake)("Threads signaled, begin processing blocked threads by VMThread");
196 const jlong start_time = os::elapsed_counter();
197 int number_of_threads_completed = 0;
198 do {
199 // Check if handshake operation has timed out
200 if (handshake_has_timed_out(start_time)) {
201 handle_timeout();
202 }
203
204 // Have VM thread perform the handshake operation for blocked threads.
205 // Observing a blocked state may of course be transient but the processing is guarded
206 // by semaphores and we optimistically begin by working on the blocked threads
207 {
208 // We need to re-think this with SMR ThreadsList.
209 // There is an assumption in the code that the Threads_lock should
210 // be locked during certain phases.
211 jtiwh.rewind();
212 MutexLocker ml(Threads_lock);
213 for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
214 // A new thread on the ThreadsList will not have an operation,
215 // hence it is skipped in handshake_process_by_vmthread.
216 if (thr->handshake_try_process_by_vmThread()) {
217 handshake_executed_by_vm_thread++;
218 }
219 }
220 }
221
222 while (poll_for_completed_thread()) {
223 // Includes canceled operations by exiting threads.
224 number_of_threads_completed++;
225 }
226
227 } while (number_of_threads_issued > number_of_threads_completed);
228 assert(number_of_threads_issued == number_of_threads_completed, "Must be the same");
229 DEBUG_ONLY(_op->check_state();)
230
231 log_handshake_info(start_time_ns, _op->name(), number_of_threads_issued, handshake_executed_by_vm_thread);
232 }
233
234 VMOp_Type type() const { return VMOp_HandshakeAllThreads; }
235 };
236
237 class VM_HandshakeFallbackOperation : public VM_Operation {
238 HandshakeClosure* _handshake_cl;
239 Thread* _target_thread;
240 bool _all_threads;
241 bool _executed;
242 public:
243 VM_HandshakeFallbackOperation(HandshakeClosure* cl) :
244 _handshake_cl(cl), _target_thread(NULL), _all_threads(true), _executed(false) {}
245 VM_HandshakeFallbackOperation(HandshakeClosure* cl, Thread* target) :
246 _handshake_cl(cl), _target_thread(target), _all_threads(false), _executed(false) {}
247
248 void doit() {
249 log_trace(handshake)("VMThread executing VM_HandshakeFallbackOperation, operation: %s", name());
250 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
251 if (_all_threads || t == _target_thread) {
252 if (t == _target_thread) {
253 _executed = true;
254 }
255 _handshake_cl->do_thread(t);
256 }
257 }
258 }
259
260 VMOp_Type type() const { return VMOp_HandshakeFallback; }
261 bool executed() const { return _executed; }
262 };
263
264 void HandshakeThreadsOperation::do_handshake(JavaThread* thread) {
265 jlong start_time_ns = 0;
266 if (log_is_enabled(Debug, handshake, task)) {
267 start_time_ns = os::javaTimeNanos();
268 }
269
270 // Only actually execute the operation for non terminated threads.
271 if (!thread->is_terminated()) {
272 _handshake_cl->do_thread(thread);
273 _executed = true;
274 }
275
276 // Use the semaphore to inform the VM thread that we have completed the operation
277 _done.signal();
278
279 if (start_time_ns != 0) {
280 jlong completion_time = os::javaTimeNanos() - start_time_ns;
281 log_debug(handshake, task)("Operation: %s for thread " PTR_FORMAT ", is_vm_thread: %s, completed in " JLONG_FORMAT " ns",
282 name(), p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread()), completion_time);
283 }
284 }
285
286 void Handshake::execute(HandshakeClosure* thread_cl) {
287 if (ThreadLocalHandshakes) {
288 HandshakeThreadsOperation cto(thread_cl);
289 VM_HandshakeAllThreads handshake(&cto);
290 VMThread::execute(&handshake);
291 } else {
292 VM_HandshakeFallbackOperation op(thread_cl);
293 VMThread::execute(&op);
294 }
295 }
296
297 bool Handshake::execute(HandshakeClosure* thread_cl, JavaThread* target) {
298 if (ThreadLocalHandshakes) {
299 HandshakeThreadsOperation cto(thread_cl);
300 VM_HandshakeOneThread handshake(&cto, target);
301 VMThread::execute(&handshake);
302 return handshake.executed();
303 } else {
304 VM_HandshakeFallbackOperation op(thread_cl, target);
305 VMThread::execute(&op);
306 return op.executed();
307 }
308 }
309
310 HandshakeState::HandshakeState() : _operation(NULL), _semaphore(1), _thread_in_process_handshake(false) {}
311
312 void HandshakeState::set_operation(JavaThread* target, HandshakeOperation* op) {
313 _operation = op;
314 SafepointMechanism::arm_local_poll_release(target);
315 }
316
317 void HandshakeState::clear_handshake(JavaThread* target) {
318 _operation = NULL;
319 SafepointMechanism::disarm_if_needed(target, true /* release */);
320 }
321
322 void HandshakeState::process_self_inner(JavaThread* thread) {
323 assert(Thread::current() == thread, "should call from thread");
324 assert(!thread->is_terminated(), "should not be a terminated thread");
325 assert(thread->thread_state() != _thread_blocked, "should not be in a blocked state");
326 assert(thread->thread_state() != _thread_in_native, "should not be in native");
327
328 do {
329 ThreadInVMForHandshake tivm(thread);
330 if (!_semaphore.trywait()) {
331 _semaphore.wait_with_safepoint_check(thread);
332 }
333 HandshakeOperation* op = Atomic::load_acquire(&_operation);
334 if (op != NULL) {
335 HandleMark hm(thread);
336 CautiouslyPreserveExceptionMark pem(thread);
337 // Disarm before execute the operation
338 clear_handshake(thread);
339 op->do_handshake(thread);
340 }
341 _semaphore.signal();
342 } while (has_operation());
343 }
344
345 bool HandshakeState::vmthread_can_process_handshake(JavaThread* target) {
346 // handshake_safe may only be called with polls armed.
347 // VM thread controls this by first claiming the handshake via claim_handshake_for_vmthread.
348 return SafepointSynchronize::handshake_safe(target);
349 }
350
351 static bool possibly_vmthread_can_process_handshake(JavaThread* target) {
352 // An externally suspended thread cannot be resumed while the
353 // Threads_lock is held so it is safe.
354 // Note that this method is allowed to produce false positives.
355 assert(Threads_lock->owned_by_self(), "Not holding Threads_lock.");
356 if (target->is_ext_suspended()) {
357 return true;
358 }
359 if (target->is_terminated()) {
360 return true;
361 }
362 switch (target->thread_state()) {
363 case _thread_in_native:
364 // native threads are safe if they have no java stack or have walkable stack
365 return !target->has_last_Java_frame() || target->frame_anchor()->walkable();
366
367 case _thread_blocked:
368 return true;
369
370 default:
371 return false;
372 }
373 }
374
375 bool HandshakeState::claim_handshake_for_vmthread() {
376 if (!_semaphore.trywait()) {
377 return false;
378 }
379 if (has_operation()) {
380 return true;
381 }
382 _semaphore.signal();
383 return false;
384 }
385
386 bool HandshakeState::try_process_by_vmThread(JavaThread* target) {
387 assert(Thread::current()->is_VM_thread(), "should call from vm thread");
388 // Threads_lock must be held here, but that is assert()ed in
389 // possibly_vmthread_can_process_handshake().
390
391 if (!has_operation()) {
392 // JT has already cleared its handshake
393 return false;
394 }
395
396 if (!possibly_vmthread_can_process_handshake(target)) {
397 // JT is observed in an unsafe state, it must notice the handshake itself
398 return false;
399 }
400
401 // Claim the semaphore if there still an operation to be executed.
402 if (!claim_handshake_for_vmthread()) {
403 return false;
404 }
405
406 // If we own the semaphore at this point and while owning the semaphore
407 // can observe a safe state the thread cannot possibly continue without
408 // getting caught by the semaphore.
409 bool executed = false;
410 if (vmthread_can_process_handshake(target)) {
411 guarantee(!_semaphore.trywait(), "we should already own the semaphore");
412 log_trace(handshake)("Processing handshake by VMThtread");
413 _operation->do_handshake(target);
414 // Disarm after VM thread have executed the operation.
415 clear_handshake(target);
416 executed = true;
417 }
418
419 // Release the thread
420 _semaphore.signal();
421
422 return executed;
423 }