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 int64_t _pending_threads;
44 bool _executed;
45 bool _is_direct;
46 public:
47 HandshakeOperation(HandshakeClosure* cl) : _handshake_cl(cl), _pending_threads(1), _executed(false), _is_direct(false) {}
48 void do_handshake(JavaThread* thread);
49 bool is_completed() {
50 assert(_pending_threads >= 0, "_pending_threads cannot be negative");
51 return _pending_threads == 0;
52 }
53 void add_target_count(int count) { Atomic::add(&_pending_threads, count); }
54 bool executed() const { return _executed; }
55 const char* name() { return _handshake_cl->name(); }
56
57 void set_isdirect() { _is_direct = true; }
58 bool is_direct() { return _is_direct; }
59
60 #ifdef ASSERT
61 void check_state() {
62 assert(_pending_threads == 0, "Must be zero");
63 }
64 #endif
65 };
66
67 class VM_Handshake: public VM_Operation {
68 const jlong _handshake_timeout;
69 public:
70 bool evaluate_at_safepoint() const { return false; }
71
72 protected:
73 HandshakeOperation* const _op;
74
75 VM_Handshake(HandshakeOperation* op) :
76 _handshake_timeout(TimeHelper::millis_to_counter(HandshakeTimeout)), _op(op) {}
77
78 bool handshake_has_timed_out(jlong start_time);
79 static void handle_timeout();
80 };
81
82 bool VM_Handshake::handshake_has_timed_out(jlong start_time) {
83 // Check if handshake operation has timed out
84 if (_handshake_timeout > 0) {
85 return os::elapsed_counter() >= (start_time + _handshake_timeout);
86 }
87 return false;
88 }
89
90 void VM_Handshake::handle_timeout() {
91 LogStreamHandle(Warning, handshake) log_stream;
92 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
93 if (thr->has_handshake()) {
94 log_stream.print("Thread " PTR_FORMAT " has not cleared its handshake op", p2i(thr));
95 thr->print_thread_state_on(&log_stream);
96 }
97 }
98 log_stream.flush();
99 fatal("Handshake operation timed out");
100 }
101
102 static void log_handshake_info(jlong start_time_ns, const char* name, int targets, int vmt_executed, const char* extra = NULL) {
103 if (start_time_ns != 0) {
104 jlong completion_time = os::javaTimeNanos() - start_time_ns;
105 log_info(handshake)("Handshake \"%s\", Targeted threads: %d, Executed by targeted threads: %d, Total completion time: " JLONG_FORMAT " ns%s%s",
106 name, targets,
107 targets - vmt_executed,
108 completion_time,
109 extra != NULL ? ", " : "",
110 extra != NULL ? extra : "");
111 }
112 }
113
114 class VM_HandshakeOneThread: public VM_Handshake {
115 JavaThread* _target;
116 public:
117 VM_HandshakeOneThread(HandshakeOperation* op, JavaThread* target) :
118 VM_Handshake(op), _target(target) {}
119
120 void doit() {
121 jlong start_time_ns = 0;
122 if (log_is_enabled(Info, handshake)) {
123 start_time_ns = os::javaTimeNanos();
124 }
125
126 ThreadsListHandle tlh;
127 if (tlh.includes(_target)) {
128 _target->set_handshake_operation(_op);
129 } else {
130 log_handshake_info(start_time_ns, _op->name(), 0, 0, "(thread dead)");
131 return;
132 }
133
134 log_trace(handshake)("JavaThread " INTPTR_FORMAT " signaled, begin attempt to process by VMThtread", p2i(_target));
135 jlong timeout_start_time = os::elapsed_counter();
136 bool by_vm_thread = false;
137 do {
138 if (handshake_has_timed_out(timeout_start_time)) {
139 handle_timeout();
140 }
141 by_vm_thread = _target->handshake_try_process(_op);
142 } while (!_op->is_completed());
143 DEBUG_ONLY(_op->check_state();)
144 log_handshake_info(start_time_ns, _op->name(), 1, by_vm_thread ? 1 : 0);
145 }
146
147 VMOp_Type type() const { return VMOp_HandshakeOneThread; }
148
149 bool executed() const { return _op->executed(); }
150 };
151
152 class VM_HandshakeAllThreads: public VM_Handshake {
153 public:
154 VM_HandshakeAllThreads(HandshakeOperation* op) : VM_Handshake(op) {}
155
156 void doit() {
157 jlong start_time_ns = 0;
158 if (log_is_enabled(Info, handshake)) {
159 start_time_ns = os::javaTimeNanos();
160 }
161 int handshake_executed_by_vm_thread = 0;
162
163 JavaThreadIteratorWithHandle jtiwh;
164 int number_of_threads_issued = 0;
165 for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
166 thr->set_handshake_operation(_op);
167 number_of_threads_issued++;
168 }
169
170 if (number_of_threads_issued < 1) {
171 log_handshake_info(start_time_ns, _op->name(), 0, 0);
172 return;
173 }
174 _op->add_target_count(number_of_threads_issued - 1);
175
176 log_trace(handshake)("Threads signaled, begin processing blocked threads by VMThread");
177 const jlong start_time = os::elapsed_counter();
178 do {
179 // Check if handshake operation has timed out
180 if (handshake_has_timed_out(start_time)) {
181 handle_timeout();
182 }
183
184 // Have VM thread perform the handshake operation for blocked threads.
185 // Observing a blocked state may of course be transient but the processing is guarded
186 // by semaphores and we optimistically begin by working on the blocked threads
187 jtiwh.rewind();
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_try_process.
191 if (thr->handshake_try_process(_op)) {
192 handshake_executed_by_vm_thread++;
193 }
194 }
195 } while (!_op->is_completed());
196 DEBUG_ONLY(_op->check_state();)
197
198 log_handshake_info(start_time_ns, _op->name(), number_of_threads_issued, handshake_executed_by_vm_thread);
199 }
200
201 VMOp_Type type() const { return VMOp_HandshakeAllThreads; }
202 };
203
204 class VM_HandshakeFallbackOperation : public VM_Operation {
205 HandshakeClosure* _handshake_cl;
206 Thread* _target_thread;
207 bool _all_threads;
208 bool _executed;
209 public:
210 VM_HandshakeFallbackOperation(HandshakeClosure* cl) :
211 _handshake_cl(cl), _target_thread(NULL), _all_threads(true), _executed(false) {}
212 VM_HandshakeFallbackOperation(HandshakeClosure* cl, Thread* target) :
213 _handshake_cl(cl), _target_thread(target), _all_threads(false), _executed(false) {}
214
215 void doit() {
216 log_trace(handshake)("VMThread executing VM_HandshakeFallbackOperation, operation: %s", name());
217 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
218 if (_all_threads || t == _target_thread) {
219 if (t == _target_thread) {
220 _executed = true;
221 }
222 _handshake_cl->do_thread(t);
223 }
224 }
225 }
226
227 VMOp_Type type() const { return VMOp_HandshakeFallback; }
228 bool executed() const { return _executed; }
229 };
230
231 void HandshakeOperation::do_handshake(JavaThread* thread) {
232 jlong start_time_ns = 0;
233 if (log_is_enabled(Debug, handshake, task)) {
234 start_time_ns = os::javaTimeNanos();
235 }
236
237 // Only actually execute the operation for non terminated threads.
238 if (!thread->is_terminated()) {
239 _handshake_cl->do_thread(thread);
240 _executed = true;
241 }
242
243 if (start_time_ns != 0) {
244 jlong completion_time = os::javaTimeNanos() - start_time_ns;
245 log_debug(handshake, task)("Operation: %s for thread " PTR_FORMAT ", is_vm_thread: %s, completed in " JLONG_FORMAT " ns",
246 name(), p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread()), completion_time);
247 }
248
249 // Inform VMThread/Handshaker that we have completed the operation
250 Atomic::dec(&_pending_threads);
251
252 // It is no longer safe to refer to 'this' as the VMThread/Handshaker may have destroyed this operation
253 }
254
255 void Handshake::execute(HandshakeClosure* thread_cl) {
256 if (SafepointMechanism::uses_thread_local_poll()) {
257 HandshakeOperation cto(thread_cl);
258 VM_HandshakeAllThreads handshake(&cto);
259 VMThread::execute(&handshake);
260 } else {
261 VM_HandshakeFallbackOperation op(thread_cl);
262 VMThread::execute(&op);
263 }
264 }
265
266 bool Handshake::execute(HandshakeClosure* thread_cl, JavaThread* target, bool is_direct_handshake) {
267 if (SafepointMechanism::uses_thread_local_poll()) {
268 HandshakeOperation ho(thread_cl);
269 if (is_direct_handshake) {
270 direct_handshake(target, &ho);
271 } else {
272 VM_HandshakeOneThread op(&ho, target);
273 VMThread::execute(&op);
274 }
275 return ho.executed();
276 } else {
277 VM_HandshakeFallbackOperation op(thread_cl, target);
278 VMThread::execute(&op);
279 return op.executed();
280 }
281 }
282
283 void Handshake::direct_handshake(JavaThread* target, HandshakeOperation *op) {
284 JavaThread *self = (JavaThread*)Thread::current();
285 op->set_isdirect();
286
287 jlong start_time_ns = 0;
288 if (log_is_enabled(Info, handshake)) {
289 start_time_ns = os::javaTimeNanos();
290 }
291
292 ThreadsListHandle tlh;
293 if (tlh.includes(target)) {
294 target->set_handshake_operation(op);
295 } else {
296 log_handshake_info(start_time_ns, op->name(), 0, 0, "(thread dead)");
297 return;
298 }
299
300 bool by_handshaker = false;
301 while (!op->is_completed()) {
302 by_handshaker = target->handshake_try_process(op);
303 // Check for pending handshakes to avoid possible deadlocks where our
304 // target is trying to handshake us.
305 if (SafepointMechanism::should_block(self)) {
306 ThreadBlockInVM tbivm(self);
307 }
308 }
309 DEBUG_ONLY(op->check_state();)
310 log_handshake_info(start_time_ns, op->name(), 1, by_handshaker ? 1 : 0);
311 }
312
313 HandshakeState::HandshakeState() : _operation(NULL), _operation_direct(NULL), _handshake_turn_sem(1), _processing_sem(1), _thread_in_process_handshake(false) {
314 DEBUG_ONLY(_active_handshaker = NULL;)
315 }
316
317 void HandshakeState::set_operation(HandshakeOperation* op) {
318 if (!op->is_direct()) {
319 _operation = op;
320 } else {
321 // Serialize direct handshakes so that only one proceeds at a time for a given target
322 _handshake_turn_sem.wait_with_safepoint_check((JavaThread*)Thread::current());
323 _operation_direct = op;
324 }
325 SafepointMechanism::arm_local_poll_release(_thread);
326 }
327
328 void HandshakeState::clear_handshake(bool is_direct) {
329 if (!is_direct) {
330 _operation = NULL;
331 } else {
332 _operation_direct = NULL;
333 _handshake_turn_sem.signal();
334 }
335 }
336
337 void HandshakeState::process_self_inner() {
338 assert(Thread::current() == _thread, "should call from thread");
339 assert(!_thread->is_terminated(), "should not be a terminated thread");
340 assert(_thread->thread_state() != _thread_blocked, "should not be in a blocked state");
341 assert(_thread->thread_state() != _thread_in_native, "should not be in native");
342
343 do {
344 ThreadInVMForHandshake tivm(_thread);
345 if (!_processing_sem.trywait()) {
346 _processing_sem.wait_with_safepoint_check(_thread);
347 }
348 bool is_direct_handshake = false;
349 HandshakeOperation* op = Atomic::load_acquire(&_operation);
350 if (op == NULL) {
351 op = Atomic::load_acquire(&_operation_direct);
352 is_direct_handshake = true;
353 }
354 if (op != NULL) {
355 HandleMark hm(_thread);
356 CautiouslyPreserveExceptionMark pem(_thread);
357 // Disarm before execute the operation
358 clear_handshake(is_direct_handshake);
359 op->do_handshake(_thread);
360 }
361 _processing_sem.signal();
362 } while (has_operation());
363 }
364
365 bool HandshakeState::can_process_handshake() {
366 // handshake_safe may only be called with polls armed.
367 // Handshaker controls this by first claiming the handshake via claim_handshake().
368 return SafepointSynchronize::handshake_safe(_thread);
369 }
370
371 bool HandshakeState::possibly_can_process_handshake() {
372 // Note that this method is allowed to produce false positives.
373 if (_thread->is_ext_suspended()) {
374 return true;
375 }
376 if (_thread->is_terminated()) {
377 return true;
378 }
379 switch (_thread->thread_state()) {
380 case _thread_in_native:
381 // native threads are safe if they have no java stack or have walkable stack
382 return !_thread->has_last_Java_frame() || _thread->frame_anchor()->walkable();
383
384 case _thread_blocked:
385 return true;
386
387 default:
388 return false;
389 }
390 }
391
392 bool HandshakeState::claim_handshake(bool is_direct) {
393 if (!_processing_sem.trywait()) {
394 return false;
395 }
396 if ((!is_direct && _operation != NULL) || (is_direct && _operation_direct != NULL)){
397 return true;
398 }
399 _processing_sem.signal();
400 return false;
401 }
402
403 bool HandshakeState::try_process(HandshakeOperation* op) {
404 bool is_direct = op->is_direct();
405
406 if ((!is_direct && _operation == NULL) || (is_direct && _operation_direct == NULL)){
407 // JT has already cleared its handshake
408 return false;
409 }
410
411 if (!possibly_can_process_handshake()) {
412 // JT is observed in an unsafe state, it must notice the handshake itself
413 return false;
414 }
415
416 // Claim the semaphore if there still an operation to be executed.
417 if (!claim_handshake(is_direct)) {
418 return false;
419 }
420
421 // Check if the handshake operation is the same as the one we meant to execute. The
422 // handshake could have been already processed by the handshakee and a new handshake
423 // by another JavaThread might be in progress.
424 if ( (is_direct && op != _operation_direct)) {
425 _processing_sem.signal();
426 return false;
427 }
428
429 // If we own the semaphore at this point and while owning the semaphore
430 // can observe a safe state the thread cannot possibly continue without
431 // getting caught by the semaphore.
432 bool executed = false;
433 if (can_process_handshake()) {
434 guarantee(!_processing_sem.trywait(), "we should already own the semaphore");
435 log_trace(handshake)("Processing handshake by %s", Thread::current()->is_VM_thread() ? "VMThread" : "Handshaker");
436 DEBUG_ONLY(_active_handshaker = Thread::current();)
437 op->do_handshake(_thread);
438 DEBUG_ONLY(_active_handshaker = NULL;)
439 // Disarm after we have executed the operation.
440 clear_handshake(is_direct);
441 executed = true;
442 }
443
444 // Release the thread
445 _processing_sem.signal();
446
447 return executed;
448 }