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 _active_handshaker(NULL) 388 { 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 _active_handshaker = Thread::current(); 517 op->do_handshake(_handshakee); 518 _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 }