1 /* 2 * Copyright (c) 2017, 2018, 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/handshake.hpp" 30 #include "runtime/interfaceSupport.inline.hpp" 31 #include "runtime/orderAccess.hpp" 32 #include "runtime/osThread.hpp" 33 #include "runtime/semaphore.inline.hpp" 34 #include "runtime/task.hpp" 35 #include "runtime/timerTrace.hpp" 36 #include "runtime/thread.hpp" 37 #include "runtime/vmThread.hpp" 38 #include "utilities/formatBuffer.hpp" 39 #include "utilities/preserveException.hpp" 40 41 class HandshakeOperation: public StackObj { 42 public: 43 virtual void do_handshake(JavaThread* thread) = 0; 44 virtual void cancel_handshake(JavaThread* thread) = 0; 45 }; 46 47 class HandshakeThreadsOperation: public HandshakeOperation { 48 static Semaphore _done; 49 ThreadClosure* _thread_cl; 50 51 public: 52 HandshakeThreadsOperation(ThreadClosure* cl) : _thread_cl(cl) {} 53 void do_handshake(JavaThread* thread); 54 void cancel_handshake(JavaThread* thread) { _done.signal(); }; 55 56 bool thread_has_completed() { return _done.trywait(); } 57 58 #ifdef ASSERT 59 void check_state() { 60 assert(!_done.trywait(), "Must be zero"); 61 } 62 #endif 63 }; 64 65 Semaphore HandshakeThreadsOperation::_done(0); 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 bool evaluate_concurrently() const { return false; } 73 74 protected: 75 HandshakeThreadsOperation* const _op; 76 77 VM_Handshake(HandshakeThreadsOperation* op) : 78 _handshake_timeout(TimeHelper::millis_to_counter(HandshakeTimeout)), _op(op) {} 79 80 void set_handshake(JavaThread* target) { 81 target->set_handshake_operation(_op); 82 } 83 84 // This method returns true for threads completed their operation 85 // and true for threads canceled their operation. 86 // A cancellation can happen if the thread is exiting. 87 bool poll_for_completed_thread() { return _op->thread_has_completed(); } 88 89 bool handshake_has_timed_out(jlong start_time); 90 static void handle_timeout(); 91 }; 92 93 bool VM_Handshake::handshake_has_timed_out(jlong start_time) { 94 // Check if handshake operation has timed out 95 if (_handshake_timeout > 0) { 96 return os::elapsed_counter() >= (start_time + _handshake_timeout); 97 } 98 return false; 99 } 100 101 void VM_Handshake::handle_timeout() { 102 LogStreamHandle(Warning, handshake) log_stream; 103 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) { 104 if (thr->has_handshake()) { 105 log_stream.print("Thread " PTR_FORMAT " has not cleared its handshake op", p2i(thr)); 106 thr->print_thread_state_on(&log_stream); 107 } 108 } 109 log_stream.flush(); 110 fatal("Handshake operation timed out"); 111 } 112 113 class VM_HandshakeOneThread: public VM_Handshake { 114 JavaThread* _target; 115 bool _thread_alive; 116 public: 117 VM_HandshakeOneThread(HandshakeThreadsOperation* op, JavaThread* target) : 118 VM_Handshake(op), _target(target), _thread_alive(false) {} 119 120 void doit() { 121 DEBUG_ONLY(_op->check_state();) 122 TraceTime timer("Performing single-target operation (vmoperation doit)", TRACETIME_LOG(Info, handshake)); 123 124 { 125 ThreadsListHandle tlh; 126 if (tlh.includes(_target)) { 127 set_handshake(_target); 128 _thread_alive = true; 129 } 130 } 131 132 if (!_thread_alive) { 133 return; 134 } 135 136 if (!UseMembar) { 137 os::serialize_thread_states(); 138 } 139 140 log_trace(handshake)("Thread signaled, begin processing by VMThtread"); 141 jlong start_time = os::elapsed_counter(); 142 do { 143 if (handshake_has_timed_out(start_time)) { 144 handle_timeout(); 145 } 146 147 // We need to re-think this with SMR ThreadsList. 148 // There is an assumption in the code that the Threads_lock should be 149 // locked during certain phases. 150 MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag); 151 ThreadsListHandle tlh; 152 if (tlh.includes(_target)) { 153 // Warning _target's address might be re-used. 154 // handshake_process_by_vmthread will check the semaphore for us again. 155 // Since we can't have more then one handshake in flight a reuse of 156 // _target's address should be okay since the new thread will not have 157 // an operation. 158 _target->handshake_process_by_vmthread(); 159 } else { 160 // We can't warn here since the thread does cancel_handshake after 161 // it has been removed from the ThreadsList. So we should just keep 162 // looping here until while below returns false. If we have a bug, 163 // then we hang here, which is good for debugging. 164 } 165 } while (!poll_for_completed_thread()); 166 DEBUG_ONLY(_op->check_state();) 167 } 168 169 VMOp_Type type() const { return VMOp_HandshakeOneThread; } 170 171 bool thread_alive() const { return _thread_alive; } 172 }; 173 174 class VM_HandshakeAllThreads: public VM_Handshake { 175 public: 176 VM_HandshakeAllThreads(HandshakeThreadsOperation* op) : VM_Handshake(op) {} 177 178 void doit() { 179 DEBUG_ONLY(_op->check_state();) 180 TraceTime timer("Performing operation (vmoperation doit)", TRACETIME_LOG(Info, handshake)); 181 182 int number_of_threads_issued = 0; 183 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) { 184 set_handshake(thr); 185 number_of_threads_issued++; 186 } 187 188 if (number_of_threads_issued < 1) { 189 log_debug(handshake)("No threads to handshake."); 190 return; 191 } 192 193 if (!UseMembar) { 194 os::serialize_thread_states(); 195 } 196 197 log_debug(handshake)("Threads signaled, begin processing blocked threads by VMThtread"); 198 const jlong start_time = os::elapsed_counter(); 199 int number_of_threads_completed = 0; 200 do { 201 // Check if handshake operation has timed out 202 if (handshake_has_timed_out(start_time)) { 203 handle_timeout(); 204 } 205 206 // Have VM thread perform the handshake operation for blocked threads. 207 // Observing a blocked state may of course be transient but the processing is guarded 208 // by semaphores and we optimistically begin by working on the blocked threads 209 { 210 // We need to re-think this with SMR ThreadsList. 211 // There is an assumption in the code that the Threads_lock should 212 // be locked during certain phases. 213 MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag); 214 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) { 215 // A new thread on the ThreadsList will not have an operation, 216 // hence it is skipped in handshake_process_by_vmthread. 217 thr->handshake_process_by_vmthread(); 218 } 219 } 220 221 while (poll_for_completed_thread()) { 222 // Includes canceled operations by exiting threads. 223 number_of_threads_completed++; 224 } 225 226 } while (number_of_threads_issued > number_of_threads_completed); 227 assert(number_of_threads_issued == number_of_threads_completed, "Must be the same"); 228 DEBUG_ONLY(_op->check_state();) 229 } 230 231 VMOp_Type type() const { return VMOp_HandshakeAllThreads; } 232 }; 233 234 class VM_HandshakeFallbackOperation : public VM_Operation { 235 ThreadClosure* _thread_cl; 236 Thread* _target_thread; 237 bool _all_threads; 238 bool _thread_alive; 239 public: 240 VM_HandshakeFallbackOperation(ThreadClosure* cl) : 241 _thread_cl(cl), _target_thread(NULL), _all_threads(true), _thread_alive(true) {} 242 VM_HandshakeFallbackOperation(ThreadClosure* cl, Thread* target) : 243 _thread_cl(cl), _target_thread(target), _all_threads(false), _thread_alive(false) {} 244 245 void doit() { 246 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) { 247 if (_all_threads || t == _target_thread) { 248 if (t == _target_thread) { 249 _thread_alive = true; 250 } 251 _thread_cl->do_thread(t); 252 } 253 } 254 } 255 256 VMOp_Type type() const { return VMOp_HandshakeFallback; } 257 bool thread_alive() const { return _thread_alive; } 258 }; 259 260 void HandshakeThreadsOperation::do_handshake(JavaThread* thread) { 261 ResourceMark rm; 262 FormatBufferResource message("Operation for thread " PTR_FORMAT ", is_vm_thread: %s", 263 p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread())); 264 TraceTime timer(message, TRACETIME_LOG(Debug, handshake, task)); 265 _thread_cl->do_thread(thread); 266 267 // Use the semaphore to inform the VM thread that we have completed the operation 268 _done.signal(); 269 } 270 271 void Handshake::execute(ThreadClosure* thread_cl) { 272 if (ThreadLocalHandshakes) { 273 HandshakeThreadsOperation cto(thread_cl); 274 VM_HandshakeAllThreads handshake(&cto); 275 VMThread::execute(&handshake); 276 } else { 277 VM_HandshakeFallbackOperation op(thread_cl); 278 VMThread::execute(&op); 279 } 280 } 281 282 bool Handshake::execute(ThreadClosure* thread_cl, JavaThread* target) { 283 if (ThreadLocalHandshakes) { 284 HandshakeThreadsOperation cto(thread_cl); 285 VM_HandshakeOneThread handshake(&cto, target); 286 VMThread::execute(&handshake); 287 return handshake.thread_alive(); 288 } else { 289 VM_HandshakeFallbackOperation op(thread_cl, target); 290 VMThread::execute(&op); 291 return op.thread_alive(); 292 } 293 } 294 295 HandshakeState::HandshakeState() : _operation(NULL), _semaphore(1), _thread_in_process_handshake(false) {} 296 297 void HandshakeState::set_operation(JavaThread* target, HandshakeOperation* op) { 298 _operation = op; 299 SafepointMechanism::arm_local_poll_release(target); 300 } 301 302 void HandshakeState::clear_handshake(JavaThread* target) { 303 _operation = NULL; 304 SafepointMechanism::disarm_local_poll_release(target); 305 } 306 307 void HandshakeState::process_self_inner(JavaThread* thread) { 308 assert(Thread::current() == thread, "should call from thread"); 309 310 if (thread->is_terminated()) { 311 // If thread is not on threads list but armed, cancel. 312 thread->cancel_handshake(); 313 return; 314 } 315 316 CautiouslyPreserveExceptionMark pem(thread); 317 ThreadInVMForHandshake tivm(thread); 318 if (!_semaphore.trywait()) { 319 _semaphore.wait_with_safepoint_check(thread); 320 } 321 HandshakeOperation* op = OrderAccess::load_acquire(&_operation); 322 if (op != NULL) { 323 // Disarm before execute the operation 324 clear_handshake(thread); 325 op->do_handshake(thread); 326 } 327 _semaphore.signal(); 328 } 329 330 void HandshakeState::cancel_inner(JavaThread* thread) { 331 assert(Thread::current() == thread, "should call from thread"); 332 assert(thread->thread_state() == _thread_in_vm, "must be in vm state"); 333 HandshakeOperation* op = _operation; 334 clear_handshake(thread); 335 if (op != NULL) { 336 op->cancel_handshake(thread); 337 } 338 } 339 340 bool HandshakeState::vmthread_can_process_handshake(JavaThread* target) { 341 // SafepointSynchronize::safepoint_safe() does not consider an externally 342 // suspended thread to be safe. However, this function must be called with 343 // the Threads_lock held so an externally suspended thread cannot be 344 // resumed thus it is safe. 345 assert(Threads_lock->owned_by_self(), "Not holding Threads_lock."); 346 return SafepointSynchronize::safepoint_safe(target, target->thread_state()) || 347 target->is_ext_suspended(); 348 } 349 350 static bool possibly_vmthread_can_process_handshake(JavaThread* target) { 351 // An externally suspended thread cannot be resumed while the 352 // Threads_lock is held so it is safe. 353 // Note that this method is allowed to produce false positives. 354 assert(Threads_lock->owned_by_self(), "Not holding Threads_lock."); 355 if (target->is_ext_suspended()) { 356 return true; 357 } 358 switch (target->thread_state()) { 359 case _thread_in_native: 360 // native threads are safe if they have no java stack or have walkable stack 361 return !target->has_last_Java_frame() || target->frame_anchor()->walkable(); 362 363 case _thread_blocked: 364 return true; 365 366 default: 367 return false; 368 } 369 } 370 371 bool HandshakeState::claim_handshake_for_vmthread() { 372 if (!_semaphore.trywait()) { 373 return false; 374 } 375 if (has_operation()) { 376 return true; 377 } 378 _semaphore.signal(); 379 return false; 380 } 381 382 void HandshakeState::process_by_vmthread(JavaThread* target) { 383 assert(Thread::current()->is_VM_thread(), "should call from vm thread"); 384 385 if (!has_operation()) { 386 // JT has already cleared its handshake 387 return; 388 } 389 390 if (!possibly_vmthread_can_process_handshake(target)) { 391 // JT is observed in an unsafe state, it must notice the handshake itself 392 return; 393 } 394 395 // Claim the semaphore if there still an operation to be executed. 396 if (!claim_handshake_for_vmthread()) { 397 return; 398 } 399 400 // If we own the semaphore at this point and while owning the semaphore 401 // can observe a safe state the thread cannot possibly continue without 402 // getting caught by the semaphore. 403 if (vmthread_can_process_handshake(target)) { 404 guarantee(!_semaphore.trywait(), "we should already own the semaphore"); 405 406 _operation->do_handshake(target); 407 // Disarm after VM thread have executed the operation. 408 clear_handshake(target); 409 // Release the thread 410 } 411 412 _semaphore.signal(); 413 }