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 cannot be negative");
57 return val == 0;
58 }
59 void add_target_count(int count) { Atomic::add(&_pending_threads, count); }
60 bool executed() const { return _executed; }
61 const char* name() { return _handshake_cl->name(); }
62
63 bool is_direct() { return _is_direct; }
64
65 #ifdef ASSERT
66 void check_state() {
67 assert(_pending_threads == 0, "Must be zero");
68 }
69 #endif
70 };
71
72 class VM_Handshake: public VM_Operation {
73 const jlong _handshake_timeout;
74 public:
75 bool evaluate_at_safepoint() const { return false; }
76
77 protected:
78 HandshakeOperation* const _op;
79
80 VM_Handshake(HandshakeOperation* op) :
81 _handshake_timeout(TimeHelper::millis_to_counter(HandshakeTimeout)), _op(op) {}
82
83 bool handshake_has_timed_out(jlong start_time);
84 static void handle_timeout();
85 };
86
87 bool VM_Handshake::handshake_has_timed_out(jlong start_time) {
88 // Check if handshake operation has timed out
89 if (_handshake_timeout > 0) {
90 return os::elapsed_counter() >= (start_time + _handshake_timeout);
91 }
92 return false;
93 }
94
95 void VM_Handshake::handle_timeout() {
96 LogStreamHandle(Warning, handshake) log_stream;
97 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
98 if (thr->has_handshake()) {
99 log_stream.print("Thread " PTR_FORMAT " has not cleared its handshake op", p2i(thr));
100 thr->print_thread_state_on(&log_stream);
101 }
102 }
103 log_stream.flush();
104 fatal("Handshake operation timed out");
105 }
106
107 static void log_handshake_info(jlong start_time_ns, const char* name, int targets, int vmt_executed, const char* extra = NULL) {
108 if (start_time_ns != 0) {
109 jlong completion_time = os::javaTimeNanos() - start_time_ns;
110 log_info(handshake)("Handshake \"%s\", Targeted threads: %d, Executed by targeted threads: %d, Total completion time: " JLONG_FORMAT " ns%s%s",
111 name, targets,
112 targets - vmt_executed,
113 completion_time,
114 extra != NULL ? ", " : "",
115 extra != NULL ? extra : "");
116 }
117 }
118
119 class VM_HandshakeOneThread: public VM_Handshake {
120 JavaThread* _target;
121 public:
122 VM_HandshakeOneThread(HandshakeOperation* op, JavaThread* target) :
123 VM_Handshake(op), _target(target) {}
124
125 void doit() {
126 jlong start_time_ns = 0;
127 if (log_is_enabled(Info, handshake)) {
128 start_time_ns = os::javaTimeNanos();
129 }
130
131 ThreadsListHandle tlh;
132 if (tlh.includes(_target)) {
133 _target->set_handshake_operation(_op);
134 } else {
135 log_handshake_info(start_time_ns, _op->name(), 0, 0, "(thread dead)");
136 return;
137 }
138
139 log_trace(handshake)("JavaThread " INTPTR_FORMAT " signaled, begin attempt to process by VMThtread", p2i(_target));
140 jlong timeout_start_time = os::elapsed_counter();
141 bool by_vm_thread = false;
142 do {
143 if (handshake_has_timed_out(timeout_start_time)) {
144 handle_timeout();
145 }
146 by_vm_thread = _target->handshake_try_process(_op);
147 } while (!_op->is_completed());
148 DEBUG_ONLY(_op->check_state();)
149 log_handshake_info(start_time_ns, _op->name(), 1, by_vm_thread ? 1 : 0);
150 }
151
152 VMOp_Type type() const { return VMOp_HandshakeOneThread; }
153
154 bool executed() const { return _op->executed(); }
155 };
156
157 class VM_HandshakeAllThreads: public VM_Handshake {
158 public:
159 VM_HandshakeAllThreads(HandshakeOperation* op) : VM_Handshake(op) {}
160
161 void doit() {
162 jlong start_time_ns = 0;
163 if (log_is_enabled(Info, handshake)) {
164 start_time_ns = os::javaTimeNanos();
165 }
166 int handshake_executed_by_vm_thread = 0;
167
168 JavaThreadIteratorWithHandle jtiwh;
169 int number_of_threads_issued = 0;
170 for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
171 thr->set_handshake_operation(_op);
172 number_of_threads_issued++;
173 }
174
175 if (number_of_threads_issued < 1) {
176 log_handshake_info(start_time_ns, _op->name(), 0, 0);
177 return;
178 }
179 // _op was created with a count == 1 so don't double count.
180 _op->add_target_count(number_of_threads_issued - 1);
181
182 log_trace(handshake)("Threads signaled, begin processing blocked threads by VMThread");
183 const jlong start_time = os::elapsed_counter();
184 do {
185 // Check if handshake operation has timed out
186 if (handshake_has_timed_out(start_time)) {
187 handle_timeout();
188 }
189
190 // Have VM thread perform the handshake operation for blocked threads.
191 // Observing a blocked state may of course be transient but the processing is guarded
192 // by semaphores and we optimistically begin by working on the blocked threads
193 jtiwh.rewind();
194 for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
195 // A new thread on the ThreadsList will not have an operation,
196 // hence it is skipped in handshake_try_process.
197 if (thr->handshake_try_process(_op)) {
198 handshake_executed_by_vm_thread++;
199 }
200 }
201 } while (!_op->is_completed());
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 void HandshakeOperation::do_handshake(JavaThread* thread) {
211 jlong start_time_ns = 0;
212 if (log_is_enabled(Debug, handshake, task)) {
213 start_time_ns = os::javaTimeNanos();
214 }
215
216 // Only actually execute the operation for non terminated threads.
217 if (!thread->is_terminated()) {
218 _handshake_cl->do_thread(thread);
219 _executed = true;
220 }
221
222 if (start_time_ns != 0) {
223 jlong completion_time = os::javaTimeNanos() - start_time_ns;
224 log_debug(handshake, task)("Operation: %s for thread " PTR_FORMAT ", is_vm_thread: %s, completed in " JLONG_FORMAT " ns",
225 name(), p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread()), completion_time);
226 }
227
228 // Inform VMThread/Handshaker that we have completed the operation
229 Atomic::dec(&_pending_threads);
230
231 // It is no longer safe to refer to 'this' as the VMThread/Handshaker may have destroyed this operation
232 }
233
234 void Handshake::execute(HandshakeClosure* thread_cl) {
235 HandshakeOperation cto(thread_cl);
236 VM_HandshakeAllThreads handshake(&cto);
237 VMThread::execute(&handshake);
238 }
239
240 bool Handshake::execute(HandshakeClosure* thread_cl, JavaThread* target) {
241 HandshakeOperation cto(thread_cl);
242 VM_HandshakeOneThread handshake(&cto, target);
243 VMThread::execute(&handshake);
244 return handshake.executed();
245 }
246
247 bool Handshake::execute_direct(HandshakeClosure* thread_cl, JavaThread* target) {
248 JavaThread* self = JavaThread::current();
249 HandshakeOperation op(thread_cl, /*is_direct*/ true);
250
251 jlong start_time_ns = 0;
252 if (log_is_enabled(Info, handshake)) {
253 start_time_ns = os::javaTimeNanos();
254 }
255
256 ThreadsListHandle tlh;
257 if (tlh.includes(target)) {
258 target->set_handshake_operation(&op);
259 } else {
260 log_handshake_info(start_time_ns, op.name(), 0, 0, "(thread dead)");
261 return false;
262 }
263
264 bool by_handshaker = false;
265 while (!op.is_completed()) {
266 by_handshaker = target->handshake_try_process(&op);
267 // Check for pending handshakes to avoid possible deadlocks where our
268 // target is trying to handshake us.
269 if (SafepointMechanism::should_block(self)) {
270 ThreadBlockInVM tbivm(self);
271 }
272 }
273 DEBUG_ONLY(op.check_state();)
274 log_handshake_info(start_time_ns, op.name(), 1, by_handshaker ? 1 : 0);
275
276 return op.executed();
277 }
278
279 HandshakeState::HandshakeState() :
280 _operation(NULL),
281 _operation_direct(NULL),
282 _handshake_turn_sem(1),
283 _processing_sem(1),
284 _thread_in_process_handshake(false)
285 {
286 DEBUG_ONLY(_active_handshaker = NULL;)
287 }
288
289 void HandshakeState::set_operation(HandshakeOperation* op) {
290 if (!op->is_direct()) {
291 assert(Thread::current()->is_VM_thread(), "should be the VMThread");
292 _operation = op;
293 } else {
294 assert(Thread::current()->is_Java_thread(), "should be a JavaThread");
295 // Serialize direct handshakes so that only one proceeds at a time for a given target
296 _handshake_turn_sem.wait_with_safepoint_check(JavaThread::current());
297 _operation_direct = op;
298 }
299 SafepointMechanism::arm_local_poll_release(_handshakee);
300 }
301
302 void HandshakeState::clear_handshake(bool is_direct) {
303 if (!is_direct) {
304 _operation = NULL;
305 } else {
306 _operation_direct = NULL;
307 _handshake_turn_sem.signal();
308 }
309 }
310
311 void HandshakeState::process_self_inner() {
312 assert(Thread::current() == _handshakee, "should call from _handshakee");
313 assert(!_handshakee->is_terminated(), "should not be a terminated thread");
314 assert(_handshakee->thread_state() != _thread_blocked, "should not be in a blocked state");
315 assert(_handshakee->thread_state() != _thread_in_native, "should not be in native");
316 JavaThread* self = _handshakee;
317
318 do {
319 ThreadInVMForHandshake tivm(self);
320 if (!_processing_sem.trywait()) {
321 _processing_sem.wait_with_safepoint_check(self);
322 }
323 if (has_operation()) {
324 HandleMark hm(self);
325 CautiouslyPreserveExceptionMark pem(self);
326 HandshakeOperation * op = _operation;
327 if (op != NULL) {
328 // Disarm before executing the operation
329 clear_handshake(/*is_direct*/ false);
330 op->do_handshake(self);
331 }
332 op = _operation_direct;
333 if (op != NULL) {
334 // Disarm before executing the operation
335 clear_handshake(/*is_direct*/ true);
336 op->do_handshake(self);
337 }
338 }
339 _processing_sem.signal();
340 } while (has_operation());
341 }
342
343 bool HandshakeState::can_process_handshake() {
344 // handshake_safe may only be called with polls armed.
345 // Handshaker controls this by first claiming the handshake via claim_handshake().
346 return SafepointSynchronize::handshake_safe(_handshakee);
347 }
348
349 bool HandshakeState::possibly_can_process_handshake() {
350 // Note that this method is allowed to produce false positives.
351 if (_handshakee->is_ext_suspended()) {
352 return true;
353 }
354 if (_handshakee->is_terminated()) {
355 return true;
356 }
357 switch (_handshakee->thread_state()) {
358 case _thread_in_native:
359 // native threads are safe if they have no java stack or have walkable stack
360 return !_handshakee->has_last_Java_frame() || _handshakee->frame_anchor()->walkable();
361
362 case _thread_blocked:
363 return true;
364
365 default:
366 return false;
367 }
368 }
369
370 bool HandshakeState::claim_handshake(bool is_direct) {
371 if (!_processing_sem.trywait()) {
372 return false;
373 }
374 if (has_specific_operation(is_direct)){
375 return true;
376 }
377 _processing_sem.signal();
378 return false;
379 }
380
381 bool HandshakeState::try_process(HandshakeOperation* op) {
382 bool is_direct = op->is_direct();
383
384 if (!has_specific_operation(is_direct)){
385 // JT has already cleared its handshake
386 return false;
387 }
388
389 if (!possibly_can_process_handshake()) {
390 // JT is observed in an unsafe state, it must notice the handshake itself
391 return false;
392 }
393
394 // Claim the semaphore if there still an operation to be executed.
395 if (!claim_handshake(is_direct)) {
396 return false;
397 }
398
399 // Check if the handshake operation is the same as the one we meant to execute. The
400 // handshake could have been already processed by the handshakee and a new handshake
401 // by another JavaThread might be in progress.
402 if ( (is_direct && op != _operation_direct)) {
403 _processing_sem.signal();
404 return false;
405 }
406
407 // If we own the semaphore at this point and while owning the semaphore
408 // can observe a safe state the thread cannot possibly continue without
409 // getting caught by the semaphore.
410 bool executed = false;
411 if (can_process_handshake()) {
412 guarantee(!_processing_sem.trywait(), "we should already own the semaphore");
413 log_trace(handshake)("Processing handshake by %s", Thread::current()->is_VM_thread() ? "VMThread" : "Handshaker");
414 DEBUG_ONLY(_active_handshaker = Thread::current();)
415 op->do_handshake(_handshakee);
416 DEBUG_ONLY(_active_handshaker = NULL;)
417 // Disarm after we have executed the operation.
418 clear_handshake(is_direct);
419 executed = true;
420 }
421
422 // Release the thread
423 _processing_sem.signal();
424
425 return executed;
426 }