1 /*
2 * Copyright (c) 2018, 2026, 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 "classfile/vmSymbols.hpp"
26 #include "gc/shared/barrierSetNMethod.hpp"
27 #include "oops/method.inline.hpp"
28 #include "oops/oop.inline.hpp"
29 #include "prims/jvmtiThreadState.inline.hpp"
30 #include "runtime/continuation.hpp"
31 #include "runtime/continuationEntry.inline.hpp"
32 #include "runtime/continuationHelper.inline.hpp"
33 #include "runtime/continuationJavaClasses.inline.hpp"
34 #include "runtime/continuationWrapper.inline.hpp"
35 #include "runtime/interfaceSupport.inline.hpp"
36 #include "runtime/javaThread.inline.hpp"
37 #include "runtime/jniHandles.inline.hpp"
38 #include "runtime/mountUnmountDisabler.hpp"
39 #include "runtime/osThread.hpp"
40 #include "runtime/vframe.inline.hpp"
41 #include "runtime/vframe_hp.hpp"
42
43 // defined in continuationFreezeThaw.cpp
44 extern "C" jint JNICALL CONT_isPinned0(JNIEnv* env, jobject cont_scope);
45
46 JVM_ENTRY(void, CONT_pin(JNIEnv* env, jclass cls)) {
47 if (!Continuation::pin(JavaThread::thread_from_jni_environment(env))) {
48 THROW_MSG(vmSymbols::java_lang_IllegalStateException(), "pin overflow");
49 }
50 }
51 JVM_END
52
53 JVM_ENTRY(void, CONT_unpin(JNIEnv* env, jclass cls)) {
54 if (!Continuation::unpin(JavaThread::thread_from_jni_environment(env))) {
55 THROW_MSG(vmSymbols::java_lang_IllegalStateException(), "pin underflow");
56 }
57 }
58 JVM_END
59
60 class UnmountBeginMark : public StackObj {
61 Handle _vthread;
62 JavaThread* _current;
63 freeze_result _result;
64 bool _failed;
65
66 public:
67 UnmountBeginMark(JavaThread* t) :
68 _vthread(t, t->vthread()), _current(t), _result(freeze_pinned_native), _failed(false) {
69 assert(!_current->is_in_vthread_transition(), "must be");
70
71 MountUnmountDisabler::start_transition(_current, _vthread(), false /*is_mount*/, false /*is_thread_start*/);
72
73 // Don't preempt if there is a pending popframe or earlyret operation. This can
74 // be installed in in process_at_transition_start() so we need to check it here.
75 if (JvmtiExport::can_pop_frame() || JvmtiExport::can_force_early_return()) {
76 JvmtiThreadState* state = _current->jvmti_thread_state();
77 if (_current->has_pending_popframe() || (state != nullptr && state->is_earlyret_pending())) {
78 _failed = true;
79 }
80 }
81
82 // Don't preempt in case there is an async exception installed since
83 // we would incorrectly throw it during the unmount logic in the carrier.
84 if (_current->has_async_exception_condition()) {
85 _failed = true;
86 }
87 }
88 ~UnmountBeginMark() {
89 assert(!_current->is_suspended()
90 JVMTI_ONLY(|| (_current->is_vthread_transition_disabler() && _result != freeze_ok)), "must be");
91 assert(_current->is_in_vthread_transition(), "must be");
92
93 if (_result != freeze_ok) {
94 // Undo transition
95 MountUnmountDisabler::end_transition(_current, _vthread(), true /*is_mount*/, false /*is_thread_start*/);
96 }
97 }
98 void set_result(freeze_result res) { _result = res; }
99 bool failed() { return _failed; }
100 };
101
102 #if INCLUDE_JVMTI
103 static bool is_vthread_safe_to_preempt_for_jvmti(JavaThread* current) {
104 if (current->is_in_vthread_transition()) {
105 // We are at the end of a mount transition.
106 return false;
107 }
108 return true;
109 }
110 #endif // INCLUDE_JVMTI
111
112 static bool is_vthread_safe_to_preempt(JavaThread* current, oop vthread) {
113 assert(java_lang_VirtualThread::is_instance(vthread), "");
114 if (java_lang_VirtualThread::state(vthread) != java_lang_VirtualThread::RUNNING) { // inside transition
115 return false;
116 }
117 return JVMTI_ONLY(is_vthread_safe_to_preempt_for_jvmti(current)) NOT_JVMTI(true);
118 }
119
120 typedef freeze_result (*FreezeContFnT)(JavaThread*, intptr_t*);
121
122 static void verify_preempt_preconditions(JavaThread* current, oop continuation) {
123 assert(current == JavaThread::current(), "no support for external preemption");
124 assert(current->has_last_Java_frame(), "");
125 assert(!current->preempting(), "");
126 assert(current->last_continuation() != nullptr, "");
127 assert(current->last_continuation()->cont_oop(current) == continuation, "");
128 assert(Continuation::continuation_scope(continuation) == java_lang_VirtualThread::vthread_scope(), "");
129 assert(!current->has_pending_exception(), "");
130 }
131
132 freeze_result Continuation::try_preempt(JavaThread* current, oop continuation) {
133 verify_preempt_preconditions(current, continuation);
134
135 if (!is_vthread_safe_to_preempt(current, current->vthread())) {
136 return freeze_pinned_native;
137 }
138
139 UnmountBeginMark ubm(current);
140 if (ubm.failed()) return freeze_pinned_native;
141 freeze_result res = CAST_TO_FN_PTR(FreezeContFnT, freeze_preempt_entry())(current, current->last_Java_sp());
142 log_trace(continuations, preempt)("try_preempt: %d", res);
143 ubm.set_result(res);
144
145 if (current->has_pending_exception()) {
146 assert(res == freeze_exception, "expecting an exception result from freeze");
147 // We don't want to throw exceptions, especially when returning
148 // from monitorenter since the compiler does not expect one. We
149 // just ignore the exception and pin the vthread to the carrier.
150 current->clear_pending_exception();
151 }
152 return res;
153 }
154
155 #ifndef PRODUCT
156 static jlong java_tid(JavaThread* thread) {
157 return java_lang_Thread::thread_id(thread->threadObj());
158 }
159 #endif
160
161 ContinuationEntry* Continuation::get_continuation_entry_for_continuation(JavaThread* thread, oop continuation) {
162 if (thread == nullptr || continuation == nullptr) {
163 return nullptr;
164 }
165
166 for (ContinuationEntry* entry = thread->last_continuation(); entry != nullptr; entry = entry->parent()) {
167 if (continuation == entry->cont_oop(thread)) {
168 return entry;
169 }
170 }
171 return nullptr;
172 }
173
174 static bool is_on_stack(JavaThread* thread, const ContinuationEntry* entry) {
175 if (entry == nullptr) {
176 return false;
177 }
178
179 assert(thread->is_in_full_stack((address)entry), "");
180 return true;
181 // return false if called when transitioning to Java on return from freeze
182 // return !thread->has_last_Java_frame() || thread->last_Java_sp() < cont->entry_sp();
183 }
184
185 bool Continuation::is_continuation_mounted(JavaThread* thread, oop continuation) {
186 return is_on_stack(thread, get_continuation_entry_for_continuation(thread, continuation));
187 }
188
189 // When walking the virtual stack, this method returns true
190 // iff the frame is a thawed continuation frame whose
191 // caller is still frozen on the h-stack.
192 // The continuation object can be extracted from the thread.
193 bool Continuation::is_cont_barrier_frame(const frame& f) {
194 assert(f.is_interpreted_frame() || f.cb() != nullptr, "");
195 if (!Continuations::enabled()) return false;
196 return is_return_barrier_entry(f.is_interpreted_frame() ? ContinuationHelper::InterpretedFrame::return_pc(f)
197 : ContinuationHelper::CompiledFrame::return_pc(f));
198 }
199
200 bool Continuation::is_return_barrier_entry(const address pc) {
201 if (!Continuations::enabled()) return false;
202 return pc == StubRoutines::cont_returnBarrier();
203 }
204
205 bool Continuation::is_continuation_enterSpecial(const frame& f) {
206 if (f.cb() == nullptr || !f.cb()->is_nmethod()) {
207 return false;
208 }
209 Method* m = f.cb()->as_nmethod()->method();
210 return (m != nullptr && m->is_continuation_enter_intrinsic());
211 }
212
213 bool Continuation::is_continuation_entry_frame(const frame& f, const RegisterMap *map) {
214 // we can do this because the entry frame is never inlined
215 Method* m = (map != nullptr && map->in_cont() && f.is_interpreted_frame())
216 ? map->stack_chunk()->interpreter_frame_method(f)
217 : ContinuationHelper::Frame::frame_method(f);
218 return m != nullptr && m->intrinsic_id() == vmIntrinsics::_Continuation_enter;
219 }
220
221 // The parameter `sp` should be the actual sp and not the unextended sp because at
222 // least on PPC64 unextended_sp < sp is possible as interpreted frames are trimmed
223 // to the actual size of the expression stack before calls. The problem there is
224 // that even unextended_sp < entry_sp < sp is possible for an interpreted frame.
225 static inline bool is_sp_in_continuation(const ContinuationEntry* entry, intptr_t* const sp) {
226 // entry_sp() returns the unextended_sp which is always greater or equal to the actual sp
227 return entry->entry_sp() > sp;
228 }
229
230 bool Continuation::is_frame_in_continuation(const ContinuationEntry* entry, const frame& f) {
231 return is_sp_in_continuation(entry, f.sp());
232 }
233
234 ContinuationEntry* Continuation::get_continuation_entry_for_sp(JavaThread* thread, intptr_t* const sp) {
235 assert(thread != nullptr, "");
236 ContinuationEntry* entry = thread->last_continuation();
237 while (entry != nullptr && !is_sp_in_continuation(entry, sp)) {
238 entry = entry->parent();
239 }
240 return entry;
241 }
242
243 ContinuationEntry* Continuation::get_continuation_entry_for_entry_frame(JavaThread* thread, const frame& f) {
244 assert(is_continuation_enterSpecial(f), "");
245 ContinuationEntry* entry = (ContinuationEntry*)f.unextended_sp();
246 assert(entry == get_continuation_entry_for_sp(thread, f.sp()-2), "mismatched entry");
247 return entry;
248 }
249
250 bool Continuation::is_frame_in_continuation(JavaThread* thread, const frame& f) {
251 return f.is_heap_frame() || (get_continuation_entry_for_sp(thread, f.sp()) != nullptr);
252 }
253
254 static frame continuation_top_frame(const ContinuationWrapper& cont, RegisterMap* map) {
255 stackChunkOop chunk = cont.last_nonempty_chunk();
256 map->set_stack_chunk(chunk);
257 return chunk != nullptr ? chunk->top_frame(map) : frame();
258 }
259
260 bool Continuation::has_last_Java_frame(oop continuation, frame* frame, RegisterMap* map) {
261 ContinuationWrapper cont(continuation);
262 if (!cont.is_empty()) {
263 *frame = continuation_top_frame(cont, map);
264 return true;
265 } else {
266 return false;
267 }
268 }
269
270 frame Continuation::last_frame(oop continuation, RegisterMap *map) {
271 assert(map != nullptr, "a map must be given");
272 return continuation_top_frame(ContinuationWrapper(continuation), map);
273 }
274
275 frame Continuation::top_frame(const frame& callee, RegisterMap* map) {
276 assert(map != nullptr, "");
277 ContinuationEntry* ce = get_continuation_entry_for_sp(map->thread(), callee.sp());
278 assert(ce != nullptr, "");
279 oop continuation = ce->cont_oop(map->thread());
280 ContinuationWrapper cont(continuation);
281 return continuation_top_frame(cont, map);
282 }
283
284 javaVFrame* Continuation::last_java_vframe(Handle continuation, RegisterMap *map) {
285 assert(map != nullptr, "a map must be given");
286 if (!ContinuationWrapper(continuation()).is_empty()) {
287 frame f = last_frame(continuation(), map);
288 for (vframe* vf = vframe::new_vframe(&f, map, nullptr); vf; vf = vf->sender()) {
289 if (vf->is_java_frame()) {
290 return javaVFrame::cast(vf);
291 }
292 }
293 }
294 return nullptr;
295 }
296
297 frame Continuation::continuation_parent_frame(RegisterMap* map) {
298 assert(map->in_cont(), "");
299 ContinuationWrapper cont(map);
300 assert(map->thread() != nullptr || !cont.is_mounted(), "");
301
302 log_develop_trace(continuations)("continuation_parent_frame");
303 if (map->update_map()) {
304 // we need to register the link address for the entry frame
305 if (cont.entry() != nullptr) {
306 cont.entry()->update_register_map(map);
307 } else {
308 map->clear();
309 }
310 }
311
312 if (!cont.is_mounted()) { // When we're walking an unmounted continuation and reached the end
313 oop parent = jdk_internal_vm_Continuation::parent(cont.continuation());
314 stackChunkOop chunk = parent != nullptr ? ContinuationWrapper(parent).last_nonempty_chunk() : nullptr;
315 if (chunk != nullptr) {
316 return chunk->top_frame(map);
317 }
318
319 map->set_stack_chunk(nullptr);
320 return frame();
321 }
322
323 map->set_stack_chunk(nullptr);
324
325 #if (defined(X86) || defined(AARCH64) || defined(RISCV64) || defined(PPC64)) && !defined(ZERO)
326 frame sender(cont.entrySP(), cont.entryFP(), cont.entryPC());
327 #else
328 frame sender = frame();
329 Unimplemented();
330 #endif
331
332 return sender;
333 }
334
335 oop Continuation::continuation_scope(oop continuation) {
336 return continuation != nullptr ? jdk_internal_vm_Continuation::scope(continuation) : nullptr;
337 }
338
339 bool Continuation::is_scope_bottom(oop cont_scope, const frame& f, const RegisterMap* map) {
340 if (cont_scope == nullptr || !is_continuation_entry_frame(f, map)) {
341 return false;
342 }
343
344 oop continuation;
345 if (map->in_cont()) {
346 continuation = map->cont();
347 } else {
348 ContinuationEntry* ce = get_continuation_entry_for_sp(map->thread(), f.sp());
349 if (ce == nullptr) {
350 return false;
351 }
352 continuation = ce->cont_oop(map->thread());
353 }
354 if (continuation == nullptr) {
355 return false;
356 }
357
358 oop sc = continuation_scope(continuation);
359 assert(sc != nullptr, "");
360 return sc == cont_scope;
361 }
362
363 bool Continuation::is_in_usable_stack(address addr, const RegisterMap* map) {
364 ContinuationWrapper cont(map);
365 stackChunkOop chunk = cont.find_chunk_by_address(addr);
366 return chunk != nullptr ? chunk->is_usable_in_chunk(addr) : false;
367 }
368
369 bool Continuation::pin(JavaThread* current) {
370 ContinuationEntry* ce = current->last_continuation();
371 if (ce == nullptr) {
372 return true; // no continuation mounted
373 }
374 return ce->pin();
375 }
376
377 bool Continuation::unpin(JavaThread* current) {
378 ContinuationEntry* ce = current->last_continuation();
379 if (ce == nullptr) {
380 return true; // no continuation mounted
381 }
382 return ce->unpin();
383 }
384
385 frame Continuation::continuation_bottom_sender(JavaThread* thread, const frame& callee, intptr_t* sender_sp) {
386 assert (thread != nullptr, "");
387 ContinuationEntry* ce = get_continuation_entry_for_sp(thread, callee.sp());
388 assert(ce != nullptr, "callee.sp(): " INTPTR_FORMAT, p2i(callee.sp()));
389
390 log_develop_debug(continuations)("continuation_bottom_sender: [" JLONG_FORMAT "] [%d] callee: " INTPTR_FORMAT
391 " sender_sp: " INTPTR_FORMAT,
392 java_tid(thread), thread->osthread()->thread_id(), p2i(callee.sp()), p2i(sender_sp));
393
394 frame entry = ce->to_frame();
395 if (callee.is_interpreted_frame()) {
396 entry.set_sp(sender_sp); // sp != unextended_sp
397 }
398 return entry;
399 }
400
401 address Continuation::get_top_return_pc_post_barrier(JavaThread* thread, address pc) {
402 ContinuationEntry* ce;
403 if (thread != nullptr && is_return_barrier_entry(pc) && (ce = thread->last_continuation()) != nullptr) {
404 return ce->entry_pc();
405 }
406 return pc;
407 }
408
409 void Continuation::set_cont_fastpath_thread_state(JavaThread* thread) {
410 assert(thread != nullptr, "");
411 bool fast = !thread->is_interp_only_mode();
412 thread->set_cont_fastpath_thread_state(fast);
413 }
414
415 void Continuation::notify_deopt(JavaThread* thread, intptr_t* sp) {
416 ContinuationEntry* entry = thread->last_continuation();
417
418 if (entry == nullptr) {
419 return;
420 }
421
422 if (is_sp_in_continuation(entry, sp)) {
423 thread->push_cont_fastpath(sp);
424 return;
425 }
426
427 ContinuationEntry* prev;
428 do {
429 prev = entry;
430 entry = entry->parent();
431 } while (entry != nullptr && !is_sp_in_continuation(entry, sp));
432
433 if (entry == nullptr) {
434 return;
435 }
436 assert(is_sp_in_continuation(entry, sp), "");
437 if (sp > prev->parent_cont_fastpath()) {
438 prev->set_parent_cont_fastpath(sp);
439 }
440 }
441
442 #ifndef PRODUCT
443 void Continuation::describe(FrameValues &values) {
444 JavaThread* thread = JavaThread::active();
445 if (thread != nullptr) {
446 for (ContinuationEntry* ce = thread->last_continuation(); ce != nullptr; ce = ce->parent()) {
447 intptr_t* bottom = ce->entry_sp();
448 if (bottom != nullptr) {
449 values.describe(-1, bottom, "continuation entry");
450 }
451 }
452 }
453 }
454 #endif
455
456 #ifdef ASSERT
457 void Continuation::debug_verify_continuation(oop contOop) {
458 if (!VerifyContinuations) {
459 return;
460 }
461 assert(contOop != nullptr, "");
462 assert(oopDesc::is_oop(contOop), "");
463 ContinuationWrapper cont(contOop);
464
465 assert(oopDesc::is_oop_or_null(cont.tail()), "");
466 assert(cont.chunk_invariant(), "");
467
468 bool nonempty_chunk = false;
469 size_t max_size = 0;
470 int num_chunks = 0;
471 int num_frames = 0;
472 int num_interpreted_frames = 0;
473 int num_oops = 0;
474
475 for (stackChunkOop chunk = cont.tail(); chunk != nullptr; chunk = chunk->parent()) {
476 log_develop_trace(continuations)("debug_verify_continuation chunk %d", num_chunks);
477 chunk->verify(&max_size, &num_oops, &num_frames, &num_interpreted_frames);
478 if (!chunk->is_empty()) {
479 nonempty_chunk = true;
480 }
481 num_chunks++;
482 }
483
484 const bool is_empty = cont.is_empty();
485 assert(!nonempty_chunk || !is_empty, "");
486 assert(is_empty == (!nonempty_chunk && cont.last_frame().is_empty()), "");
487 }
488
489 void Continuation::print(oop continuation) { print_on(tty, continuation); }
490
491 void Continuation::print_on(outputStream* st, oop continuation) {
492 ContinuationWrapper cont(continuation);
493
494 st->print_cr("CONTINUATION: " PTR_FORMAT " done: %d",
495 continuation->identity_hash(), jdk_internal_vm_Continuation::done(continuation));
496 st->print_cr("CHUNKS:");
497 for (stackChunkOop chunk = cont.tail(); chunk != nullptr; chunk = chunk->parent()) {
498 st->print("* ");
499 chunk->print_on(true, st);
500 }
501 }
502 #endif // ASSERT
503
504
505 void continuations_init() { Continuations::init(); }
506
507 void Continuations::init() {
508 Continuation::init();
509 }
510
511 bool Continuations::enabled() {
512 return VMContinuations;
513 }
514
515 #define CC (char*) /*cast a literal from (const char*)*/
516 #define FN_PTR(f) CAST_FROM_FN_PTR(void*, &f)
517
518 static JNINativeMethod CONT_methods[] = {
519 {CC"pin", CC"()V", FN_PTR(CONT_pin)},
520 {CC"unpin", CC"()V", FN_PTR(CONT_unpin)},
521 {CC"isPinned0", CC"(Ljdk/internal/vm/ContinuationScope;)I", FN_PTR(CONT_isPinned0)},
522 };
523
524 void CONT_RegisterNativeMethods(JNIEnv *env, jclass cls) {
525 JavaThread* thread = JavaThread::current();
526 ThreadToNativeFromVM trans(thread);
527 int status = env->RegisterNatives(cls, CONT_methods, sizeof(CONT_methods)/sizeof(JNINativeMethod));
528 guarantee(status == JNI_OK, "register jdk.internal.vm.Continuation natives");
529 guarantee(!env->ExceptionCheck(), "register jdk.internal.vm.Continuation natives");
530 }