1 /*
2 * Copyright (c) 2017, 2020, 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
41 class HandshakeOperation: public StackObj {
42 HandshakeClosure* _handshake_cl;
43 int32_t _pending_threads;
44 bool _executed;
45 bool _is_direct;
46 public:
47 HandshakeOperation(HandshakeClosure* cl, bool is_direct = false) :
48 _handshake_cl(cl),
49 _pending_threads(1),
50 _executed(false),
51 _is_direct(is_direct) {}
52
53 void do_handshake(JavaThread* thread);
54 bool is_completed() {
55 int32_t val = Atomic::load(&_pending_threads);
56 assert(val >= 0, "_pending_threads=%d cannot be negative", val);
57 return val == 0;
58 }
59 void add_target_count(int count) { Atomic::add(&_pending_threads, count, memory_order_relaxed); }
60 bool executed() const { return _executed; }
61 const char* name() { return _handshake_cl->name(); }
62
63 bool is_direct() { return _is_direct; }
64 };
65
66 // Performing handshakes requires a custom yielding strategy because without it
67 // there is a clear performance regression vs plain spinning. We keep track of
68 // when we last saw progress by looking at why each targeted thread has not yet
69 // completed its handshake. After spinning for a while with no progress we will
70 // yield, but as long as there is progress, we keep spinning. Thus we avoid
71 // yielding when there is potential work to be done or the handshake is close
72 // to being finished.
73 class HandshakeSpinYield : public StackObj {
74 private:
75 jlong _start_time_ns;
76 jlong _last_spin_start_ns;
77 jlong _spin_time_ns;
78
79 int _result_count[2][HandshakeState::_number_states];
80 int _prev_result_pos;
81
82 int prev_result_pos() { return _prev_result_pos & 0x1; }
83 int current_result_pos() { return (_prev_result_pos + 1) & 0x1; }
84
85 void wait_raw(jlong now) {
86 // We start with fine-grained nanosleeping until a millisecond has
87 // passed, at which point we resort to plain naked_short_sleep.
88 if (now - _start_time_ns < NANOSECS_PER_MILLISEC) {
89 os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
90 } else {
91 os::naked_short_sleep(1);
92 }
93 }
94
95 void wait_blocked(JavaThread* self, jlong now) {
96 ThreadBlockInVM tbivm(self);
97 wait_raw(now);
98 }
99
100 bool state_changed() {
101 for (int i = 0; i < HandshakeState::_number_states; i++) {
102 if (_result_count[0][i] != _result_count[1][i]) {
103 return true;
104 }
105 }
106 return false;
107 }
108
109 void reset_state() {
110 _prev_result_pos++;
111 for (int i = 0; i < HandshakeState::_number_states; i++) {
112 _result_count[current_result_pos()][i] = 0;
113 }
114 }
115
116 public:
117 HandshakeSpinYield(jlong start_time) :
118 _start_time_ns(start_time), _last_spin_start_ns(start_time),
119 _spin_time_ns(0), _result_count(), _prev_result_pos(0) {
120
121 const jlong max_spin_time_ns = 100 /* us */ * (NANOUNITS / MICROUNITS);
122 int free_cpus = os::active_processor_count() - 1;
123 _spin_time_ns = (5 /* us */ * (NANOUNITS / MICROUNITS)) * free_cpus; // zero on UP
124 _spin_time_ns = _spin_time_ns > max_spin_time_ns ? max_spin_time_ns : _spin_time_ns;
125 }
126
127 void add_result(HandshakeState::ProcessResult pr) {
128 _result_count[current_result_pos()][pr]++;
129 }
130
131 void process() {
132 jlong now = os::javaTimeNanos();
133 if (state_changed()) {
134 reset_state();
135 // We spin for x amount of time since last state change.
136 _last_spin_start_ns = now;
137 return;
138 }
139 jlong wait_target = _last_spin_start_ns + _spin_time_ns;
140 if (wait_target < now) {
141 // On UP this is always true.
142 Thread* self = Thread::current();
143 if (self->is_Java_thread()) {
144 wait_blocked((JavaThread*)self, now);
145 } else {
146 wait_raw(now);
147 }
148 _last_spin_start_ns = os::javaTimeNanos();
149 }
150 reset_state();
151 }
152 };
153
154 class VM_Handshake: public VM_Operation {
155 const jlong _handshake_timeout;
156 public:
157 bool evaluate_at_safepoint() const { return false; }
158
159 protected:
160 HandshakeOperation* const _op;
161
162 VM_Handshake(HandshakeOperation* op) :
163 _handshake_timeout(TimeHelper::millis_to_counter(HandshakeTimeout)), _op(op) {}
164
165 bool handshake_has_timed_out(jlong start_time);
166 static void handle_timeout();
167 };
168
169 bool VM_Handshake::handshake_has_timed_out(jlong start_time) {
170 // Check if handshake operation has timed out
171 if (_handshake_timeout > 0) {
172 return os::javaTimeNanos() >= (start_time + _handshake_timeout);
173 }
174 return false;
175 }
176
177 void VM_Handshake::handle_timeout() {
178 LogStreamHandle(Warning, handshake) log_stream;
179 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
180 if (thr->has_handshake()) {
181 log_stream.print("Thread " PTR_FORMAT " has not cleared its handshake op", p2i(thr));
182 thr->print_thread_state_on(&log_stream);
183 }
184 }
185 log_stream.flush();
186 fatal("Handshake operation timed out");
187 }
188
189 static void log_handshake_info(jlong start_time_ns, const char* name, int targets, int vmt_executed, const char* extra = NULL) {
190 if (start_time_ns != 0) {
191 jlong completion_time = os::javaTimeNanos() - start_time_ns;
192 log_info(handshake)("Handshake \"%s\", Targeted threads: %d, Executed by targeted threads: %d, Total completion time: " JLONG_FORMAT " ns%s%s",
193 name, targets,
194 targets - vmt_executed,
195 completion_time,
196 extra != NULL ? ", " : "",
197 extra != NULL ? extra : "");
198 }
199 }
200
201 class VM_HandshakeOneThread: public VM_Handshake {
202 JavaThread* _target;
203 public:
204 VM_HandshakeOneThread(HandshakeOperation* op, JavaThread* target) :
205 VM_Handshake(op), _target(target) {}
206
207 void doit() {
208 jlong start_time_ns = os::javaTimeNanos();
209
210 ThreadsListHandle tlh;
211 if (tlh.includes(_target)) {
212 _target->set_handshake_operation(_op);
213 } else {
214 log_handshake_info(start_time_ns, _op->name(), 0, 0, "(thread dead)");
215 return;
216 }
217
218 log_trace(handshake)("JavaThread " INTPTR_FORMAT " signaled, begin attempt to process by VMThtread", p2i(_target));
219 HandshakeState::ProcessResult pr = HandshakeState::_no_operation;
220 HandshakeSpinYield hsy(start_time_ns);
221 do {
222 if (handshake_has_timed_out(start_time_ns)) {
223 handle_timeout();
224 }
225 pr = _target->handshake_try_process(_op);
226 hsy.add_result(pr);
227 hsy.process();
228 } while (!_op->is_completed());
229
230 // This pairs up with the release store in do_handshake(). It prevents future
231 // loads from floating above the load of _pending_threads in is_completed()
232 // and thus prevents reading stale data modified in the handshake closure
233 // by the Handshakee.
234 OrderAccess::acquire();
235
236 log_handshake_info(start_time_ns, _op->name(), 1, (pr == HandshakeState::_success) ? 1 : 0);
237 }
238
239 VMOp_Type type() const { return VMOp_HandshakeOneThread; }
240
241 bool executed() const { return _op->executed(); }
242 };
243
244 class VM_HandshakeAllThreads: public VM_Handshake {
245 public:
246 VM_HandshakeAllThreads(HandshakeOperation* op) : VM_Handshake(op) {}
247
248 void doit() {
249 jlong start_time_ns = os::javaTimeNanos();
250 int handshake_executed_by_vm_thread = 0;
251
252 JavaThreadIteratorWithHandle jtiwh;
253 int number_of_threads_issued = 0;
254 for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
255 thr->set_handshake_operation(_op);
256 number_of_threads_issued++;
257 }
258
259 if (number_of_threads_issued < 1) {
260 log_handshake_info(start_time_ns, _op->name(), 0, 0);
261 return;
262 }
263 // _op was created with a count == 1 so don't double count.
264 _op->add_target_count(number_of_threads_issued - 1);
265
266 log_trace(handshake)("Threads signaled, begin processing blocked threads by VMThread");
267 HandshakeSpinYield hsy(start_time_ns);
268 do {
269 // Check if handshake operation has timed out
270 if (handshake_has_timed_out(start_time_ns)) {
271 handle_timeout();
272 }
273
274 // Have VM thread perform the handshake operation for blocked threads.
275 // Observing a blocked state may of course be transient but the processing is guarded
276 // by semaphores and we optimistically begin by working on the blocked threads
277 jtiwh.rewind();
278 for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
279 // A new thread on the ThreadsList will not have an operation,
280 // hence it is skipped in handshake_try_process.
281 HandshakeState::ProcessResult pr = thr->handshake_try_process(_op);
282 if (pr == HandshakeState::_success) {
283 handshake_executed_by_vm_thread++;
284 }
285 hsy.add_result(pr);
286 }
287 hsy.process();
288 } while (!_op->is_completed());
289
290 // This pairs up with the release store in do_handshake(). It prevents future
291 // loads from floating above the load of _pending_threads in is_completed()
292 // and thus prevents reading stale data modified in the handshake closure
293 // by the Handshakee.
294 OrderAccess::acquire();
295
296 log_handshake_info(start_time_ns, _op->name(), number_of_threads_issued, handshake_executed_by_vm_thread);
297 }
298
299 VMOp_Type type() const { return VMOp_HandshakeAllThreads; }
300 };
301
302 void HandshakeOperation::do_handshake(JavaThread* thread) {
303 jlong start_time_ns = 0;
304 if (log_is_enabled(Debug, handshake, task)) {
305 start_time_ns = os::javaTimeNanos();
306 }
307
308 // Only actually execute the operation for non terminated threads.
309 if (!thread->is_terminated()) {
310 _handshake_cl->do_thread(thread);
311 _executed = true;
312 }
313
314 if (start_time_ns != 0) {
315 jlong completion_time = os::javaTimeNanos() - start_time_ns;
316 log_debug(handshake, task)("Operation: %s for thread " PTR_FORMAT ", is_vm_thread: %s, completed in " JLONG_FORMAT " ns",
317 name(), p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread()), completion_time);
318 }
319
320 // Inform VMThread/Handshaker that we have completed the operation.
321 // When this is executed by the Handshakee we need a release store
322 // here to make sure memory operations executed in the handshake
323 // closure are visible to the VMThread/Handshaker after it reads
324 // that the operation has completed.
325 Atomic::dec(&_pending_threads, memory_order_release);
326
327 // It is no longer safe to refer to 'this' as the VMThread/Handshaker may have destroyed this operation
328 }
329
330 void Handshake::execute(HandshakeClosure* thread_cl) {
331 HandshakeOperation cto(thread_cl);
332 VM_HandshakeAllThreads handshake(&cto);
333 VMThread::execute(&handshake);
334 }
335
336 bool Handshake::execute(HandshakeClosure* thread_cl, JavaThread* target) {
337 HandshakeOperation cto(thread_cl);
338 VM_HandshakeOneThread handshake(&cto, target);
339 VMThread::execute(&handshake);
340 return handshake.executed();
341 }
342
343 bool Handshake::execute_direct(HandshakeClosure* thread_cl, JavaThread* target) {
344 JavaThread* self = JavaThread::current();
345 HandshakeOperation op(thread_cl, /*is_direct*/ true);
346
347 jlong start_time_ns = os::javaTimeNanos();
348
349 ThreadsListHandle tlh;
350 if (tlh.includes(target)) {
351 target->set_handshake_operation(&op);
352 } else {
353 log_handshake_info(start_time_ns, op.name(), 0, 0, "(thread dead)");
354 return false;
355 }
356
357 HandshakeState::ProcessResult pr = HandshakeState::_no_operation;
358 HandshakeSpinYield hsy(start_time_ns);
359 while (!op.is_completed()) {
360 HandshakeState::ProcessResult pr = target->handshake_try_process(&op);
361 hsy.add_result(pr);
362 // Check for pending handshakes to avoid possible deadlocks where our
363 // target is trying to handshake us.
364 if (SafepointMechanism::should_block(self)) {
365 ThreadBlockInVM tbivm(self);
366 }
367 hsy.process();
368 }
369
370 // This pairs up with the release store in do_handshake(). It prevents future
371 // loads from floating above the load of _pending_threads in is_completed()
372 // and thus prevents reading stale data modified in the handshake closure
373 // by the Handshakee.
374 OrderAccess::acquire();
375
376 log_handshake_info(start_time_ns, op.name(), 1, (pr == HandshakeState::_success) ? 1 : 0);
377
378 return op.executed();
379 }
380
381 HandshakeState::HandshakeState() :
382 _operation(NULL),
383 _operation_direct(NULL),
384 _handshake_turn_sem(1),
385 _processing_sem(1),
386 _thread_in_process_handshake(false)
387 {
388 DEBUG_ONLY(_active_handshaker = NULL;)
389 }
390
391 void HandshakeState::set_operation(HandshakeOperation* op) {
392 if (!op->is_direct()) {
393 assert(Thread::current()->is_VM_thread(), "should be the VMThread");
394 _operation = op;
395 } else {
396 assert(Thread::current()->is_Java_thread(), "should be a JavaThread");
397 // Serialize direct handshakes so that only one proceeds at a time for a given target
398 _handshake_turn_sem.wait_with_safepoint_check(JavaThread::current());
399 _operation_direct = op;
400 }
401 SafepointMechanism::arm_local_poll_release(_handshakee);
402 }
403
404 void HandshakeState::clear_handshake(bool is_direct) {
405 if (!is_direct) {
406 _operation = NULL;
407 } else {
408 _operation_direct = NULL;
409 _handshake_turn_sem.signal();
410 }
411 }
412
413 void HandshakeState::process_self_inner() {
414 assert(Thread::current() == _handshakee, "should call from _handshakee");
415 assert(!_handshakee->is_terminated(), "should not be a terminated thread");
416 assert(_handshakee->thread_state() != _thread_blocked, "should not be in a blocked state");
417 assert(_handshakee->thread_state() != _thread_in_native, "should not be in native");
418 JavaThread* self = _handshakee;
419
420 do {
421 ThreadInVMForHandshake tivm(self);
422 if (!_processing_sem.trywait()) {
423 _processing_sem.wait_with_safepoint_check(self);
424 }
425 if (has_operation()) {
426 HandleMark hm(self);
427 CautiouslyPreserveExceptionMark pem(self);
428 HandshakeOperation * op = _operation;
429 if (op != NULL) {
430 // Disarm before executing the operation
431 clear_handshake(/*is_direct*/ false);
432 op->do_handshake(self);
433 }
434 op = _operation_direct;
435 if (op != NULL) {
436 // Disarm before executing the operation
437 clear_handshake(/*is_direct*/ true);
438 op->do_handshake(self);
439 }
440 }
441 _processing_sem.signal();
442 } while (has_operation());
443 }
444
445 bool HandshakeState::can_process_handshake() {
446 // handshake_safe may only be called with polls armed.
447 // Handshaker controls this by first claiming the handshake via claim_handshake().
448 return SafepointSynchronize::handshake_safe(_handshakee);
449 }
450
451 bool HandshakeState::possibly_can_process_handshake() {
452 // Note that this method is allowed to produce false positives.
453 if (_handshakee->is_ext_suspended()) {
454 return true;
455 }
456 if (_handshakee->is_terminated()) {
457 return true;
458 }
459 switch (_handshakee->thread_state()) {
460 case _thread_in_native:
461 // native threads are safe if they have no java stack or have walkable stack
462 return !_handshakee->has_last_Java_frame() || _handshakee->frame_anchor()->walkable();
463
464 case _thread_blocked:
465 return true;
466
467 default:
468 return false;
469 }
470 }
471
472 bool HandshakeState::claim_handshake(bool is_direct) {
473 if (!_processing_sem.trywait()) {
474 return false;
475 }
476 if (has_specific_operation(is_direct)){
477 return true;
478 }
479 _processing_sem.signal();
480 return false;
481 }
482
483 HandshakeState::ProcessResult HandshakeState::try_process(HandshakeOperation* op) {
484 bool is_direct = op->is_direct();
485
486 if (!has_specific_operation(is_direct)){
487 // JT has already cleared its handshake
488 return _no_operation;
489 }
490
491 if (!possibly_can_process_handshake()) {
492 // JT is observed in an unsafe state, it must notice the handshake itself
493 return _not_safe;
494 }
495
496 // Claim the semaphore if there still an operation to be executed.
497 if (!claim_handshake(is_direct)) {
498 return _state_busy;
499 }
500
501 // Check if the handshake operation is the same as the one we meant to execute. The
502 // handshake could have been already processed by the handshakee and a new handshake
503 // by another JavaThread might be in progress.
504 if (is_direct && op != _operation_direct) {
505 _processing_sem.signal();
506 return _no_operation;
507 }
508
509 // If we own the semaphore at this point and while owning the semaphore
510 // can observe a safe state the thread cannot possibly continue without
511 // getting caught by the semaphore.
512 ProcessResult pr = _not_safe;
513 if (can_process_handshake()) {
514 guarantee(!_processing_sem.trywait(), "we should already own the semaphore");
515 log_trace(handshake)("Processing handshake by %s", Thread::current()->is_VM_thread() ? "VMThread" : "Handshaker");
516 DEBUG_ONLY(_active_handshaker = Thread::current();)
517 op->do_handshake(_handshakee);
518 DEBUG_ONLY(_active_handshaker = NULL;)
519 // Disarm after we have executed the operation.
520 clear_handshake(is_direct);
521 pr = _success;
522 }
523
524 // Release the thread
525 _processing_sem.signal();
526
527 return pr;
528 }