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 ContinuationEntry* Continuation::get_continuation_entry_for_continuation(JavaThread* thread, oop continuation) {
156 if (thread == nullptr || continuation == nullptr) {
157 return nullptr;
158 }
159
160 for (ContinuationEntry* entry = thread->last_continuation(); entry != nullptr; entry = entry->parent()) {
161 if (continuation == entry->cont_oop(thread)) {
162 return entry;
163 }
164 }
165 return nullptr;
166 }
167
168 static bool is_on_stack(JavaThread* thread, const ContinuationEntry* entry) {
169 if (entry == nullptr) {
170 return false;
171 }
172
173 assert(thread->is_in_full_stack((address)entry), "");
174 return true;
175 // return false if called when transitioning to Java on return from freeze
176 // return !thread->has_last_Java_frame() || thread->last_Java_sp() < cont->entry_sp();
177 }
178
179 bool Continuation::is_continuation_mounted(JavaThread* thread, oop continuation) {
180 return is_on_stack(thread, get_continuation_entry_for_continuation(thread, continuation));
181 }
182
183 // When walking the virtual stack, this method returns true
184 // iff the frame is a thawed continuation frame whose
185 // caller is still frozen on the h-stack.
186 // The continuation object can be extracted from the thread.
187 bool Continuation::is_cont_barrier_frame(const frame& f) {
188 assert(f.is_interpreted_frame() || f.cb() != nullptr, "");
189 if (!Continuations::enabled()) return false;
190 return is_return_barrier_entry(f.is_interpreted_frame() ? ContinuationHelper::InterpretedFrame::return_pc(f)
191 : ContinuationHelper::CompiledFrame::return_pc(f));
192 }
193
194 bool Continuation::is_return_barrier_entry(const address pc) {
195 if (!Continuations::enabled()) return false;
196 return pc == StubRoutines::cont_returnBarrier();
197 }
198
199 bool Continuation::is_continuation_enterSpecial(const frame& f) {
200 if (f.cb() == nullptr || !f.cb()->is_nmethod()) {
201 return false;
202 }
203 Method* m = f.cb()->as_nmethod()->method();
204 return (m != nullptr && m->is_continuation_enter_intrinsic());
205 }
206
207 bool Continuation::is_continuation_entry_frame(const frame& f, const RegisterMap *map) {
208 // we can do this because the entry frame is never inlined
209 Method* m = (map != nullptr && map->in_cont() && f.is_interpreted_frame())
210 ? map->stack_chunk()->interpreter_frame_method(f)
211 : ContinuationHelper::Frame::frame_method(f);
212 return m != nullptr && m->intrinsic_id() == vmIntrinsics::_Continuation_enter;
213 }
214
215 // The parameter `sp` should be the actual sp and not the unextended sp because at
216 // least on PPC64 unextended_sp < sp is possible as interpreted frames are trimmed
217 // to the actual size of the expression stack before calls. The problem there is
218 // that even unextended_sp < entry_sp < sp is possible for an interpreted frame.
219 static inline bool is_sp_in_continuation(const ContinuationEntry* entry, intptr_t* const sp) {
220 // entry_sp() returns the unextended_sp which is always greater or equal to the actual sp
221 return entry->entry_sp() > sp;
222 }
223
224 bool Continuation::is_frame_in_continuation(const ContinuationEntry* entry, const frame& f) {
225 return is_sp_in_continuation(entry, f.sp());
226 }
227
228 ContinuationEntry* Continuation::get_continuation_entry_for_sp(JavaThread* thread, intptr_t* const sp) {
229 assert(thread != nullptr, "");
230 ContinuationEntry* entry = thread->last_continuation();
231 while (entry != nullptr && !is_sp_in_continuation(entry, sp)) {
232 entry = entry->parent();
233 }
234 return entry;
235 }
236
237 ContinuationEntry* Continuation::get_continuation_entry_for_entry_frame(JavaThread* thread, const frame& f) {
238 assert(is_continuation_enterSpecial(f), "");
239 ContinuationEntry* entry = (ContinuationEntry*)f.unextended_sp();
240 assert(entry == get_continuation_entry_for_sp(thread, f.sp()-2), "mismatched entry");
241 return entry;
242 }
243
244 bool Continuation::is_frame_in_continuation(JavaThread* thread, const frame& f) {
245 return f.is_heap_frame() || (get_continuation_entry_for_sp(thread, f.sp()) != nullptr);
246 }
247
248 static frame continuation_top_frame(const ContinuationWrapper& cont, RegisterMap* map) {
249 stackChunkOop chunk = cont.last_nonempty_chunk();
250 map->set_stack_chunk(chunk);
251 return chunk != nullptr ? chunk->top_frame(map) : frame();
252 }
253
254 bool Continuation::has_last_Java_frame(oop continuation, frame* frame, RegisterMap* map) {
255 ContinuationWrapper cont(continuation);
256 if (!cont.is_empty()) {
257 *frame = continuation_top_frame(cont, map);
258 return true;
259 } else {
260 return false;
261 }
262 }
263
264 frame Continuation::last_frame(oop continuation, RegisterMap *map) {
265 assert(map != nullptr, "a map must be given");
266 return continuation_top_frame(ContinuationWrapper(continuation), map);
267 }
268
269 frame Continuation::top_frame(const frame& callee, RegisterMap* map) {
270 assert(map != nullptr, "");
271 ContinuationEntry* ce = get_continuation_entry_for_sp(map->thread(), callee.sp());
272 assert(ce != nullptr, "");
273 oop continuation = ce->cont_oop(map->thread());
274 ContinuationWrapper cont(continuation);
275 return continuation_top_frame(cont, map);
276 }
277
278 javaVFrame* Continuation::last_java_vframe(Handle continuation, RegisterMap *map) {
279 assert(map != nullptr, "a map must be given");
280 if (!ContinuationWrapper(continuation()).is_empty()) {
281 frame f = last_frame(continuation(), map);
282 for (vframe* vf = vframe::new_vframe(&f, map, nullptr); vf; vf = vf->sender()) {
283 if (vf->is_java_frame()) {
284 return javaVFrame::cast(vf);
285 }
286 }
287 }
288 return nullptr;
289 }
290
291 frame Continuation::continuation_parent_frame(RegisterMap* map) {
292 assert(map->in_cont(), "");
293 ContinuationWrapper cont(map);
294 assert(map->thread() != nullptr || !cont.is_mounted(), "");
295
296 log_develop_trace(continuations)("continuation_parent_frame");
297 if (map->update_map()) {
298 // we need to register the link address for the entry frame
299 if (cont.entry() != nullptr) {
300 cont.entry()->update_register_map(map);
301 } else {
302 map->clear();
303 }
304 }
305
306 if (!cont.is_mounted()) { // When we're walking an unmounted continuation and reached the end
307 oop parent = jdk_internal_vm_Continuation::parent(cont.continuation());
308 stackChunkOop chunk = parent != nullptr ? ContinuationWrapper(parent).last_nonempty_chunk() : nullptr;
309 if (chunk != nullptr) {
310 return chunk->top_frame(map);
311 }
312
313 map->set_stack_chunk(nullptr);
314 return frame();
315 }
316
317 map->set_stack_chunk(nullptr);
318
319 #if (defined(X86) || defined(AARCH64) || defined(RISCV64) || defined(PPC64)) && !defined(ZERO)
320 frame sender(cont.entrySP(), cont.entryFP(), cont.entryPC());
321 #else
322 frame sender = frame();
323 Unimplemented();
324 #endif
325
326 return sender;
327 }
328
329 oop Continuation::continuation_scope(oop continuation) {
330 return continuation != nullptr ? jdk_internal_vm_Continuation::scope(continuation) : nullptr;
331 }
332
333 bool Continuation::is_scope_bottom(oop cont_scope, const frame& f, const RegisterMap* map) {
334 if (cont_scope == nullptr || !is_continuation_entry_frame(f, map)) {
335 return false;
336 }
337
338 oop continuation;
339 if (map->in_cont()) {
340 continuation = map->cont();
341 } else {
342 ContinuationEntry* ce = get_continuation_entry_for_sp(map->thread(), f.sp());
343 if (ce == nullptr) {
344 return false;
345 }
346 continuation = ce->cont_oop(map->thread());
347 }
348 if (continuation == nullptr) {
349 return false;
350 }
351
352 oop sc = continuation_scope(continuation);
353 assert(sc != nullptr, "");
354 return sc == cont_scope;
355 }
356
357 bool Continuation::is_in_usable_stack(address addr, const RegisterMap* map) {
358 ContinuationWrapper cont(map);
359 stackChunkOop chunk = cont.find_chunk_by_address(addr);
360 return chunk != nullptr ? chunk->is_usable_in_chunk(addr) : false;
361 }
362
363 bool Continuation::pin(JavaThread* current) {
364 ContinuationEntry* ce = current->last_continuation();
365 if (ce == nullptr) {
366 return true; // no continuation mounted
367 }
368 return ce->pin();
369 }
370
371 bool Continuation::unpin(JavaThread* current) {
372 ContinuationEntry* ce = current->last_continuation();
373 if (ce == nullptr) {
374 return true; // no continuation mounted
375 }
376 return ce->unpin();
377 }
378
379 frame Continuation::continuation_bottom_sender(JavaThread* thread, const frame& callee, intptr_t* sender_sp) {
380 assert (thread != nullptr, "");
381 ContinuationEntry* ce = get_continuation_entry_for_sp(thread, callee.sp());
382 assert(ce != nullptr, "callee.sp(): " INTPTR_FORMAT, p2i(callee.sp()));
383
384 log_develop_debug(continuations)("continuation_bottom_sender: [%d] callee: " INTPTR_FORMAT " sender_sp: " INTPTR_FORMAT,
385 thread->osthread()->thread_id(), p2i(callee.sp()), p2i(sender_sp));
386
387 frame entry = ce->to_frame();
388 if (callee.is_interpreted_frame()) {
389 entry.set_sp(sender_sp); // sp != unextended_sp
390 }
391 return entry;
392 }
393
394 address Continuation::get_top_return_pc_post_barrier(JavaThread* thread, address pc) {
395 ContinuationEntry* ce;
396 if (thread != nullptr && is_return_barrier_entry(pc) && (ce = thread->last_continuation()) != nullptr) {
397 return ce->entry_pc();
398 }
399 return pc;
400 }
401
402 void Continuation::set_cont_fastpath_thread_state(JavaThread* thread) {
403 assert(thread != nullptr, "");
404 bool fast = !thread->is_interp_only_mode();
405 thread->set_cont_fastpath_thread_state(fast);
406 }
407
408 void Continuation::notify_deopt(JavaThread* thread, intptr_t* sp) {
409 ContinuationEntry* entry = thread->last_continuation();
410
411 if (entry == nullptr) {
412 return;
413 }
414
415 if (is_sp_in_continuation(entry, sp)) {
416 thread->push_cont_fastpath(sp);
417 return;
418 }
419
420 ContinuationEntry* prev;
421 do {
422 prev = entry;
423 entry = entry->parent();
424 } while (entry != nullptr && !is_sp_in_continuation(entry, sp));
425
426 if (entry == nullptr) {
427 return;
428 }
429 assert(is_sp_in_continuation(entry, sp), "");
430 if (sp > prev->parent_cont_fastpath()) {
431 prev->set_parent_cont_fastpath(sp);
432 }
433 }
434
435 #ifndef PRODUCT
436 void Continuation::describe(FrameValues &values) {
437 JavaThread* thread = JavaThread::active();
438 if (thread != nullptr) {
439 for (ContinuationEntry* ce = thread->last_continuation(); ce != nullptr; ce = ce->parent()) {
440 intptr_t* bottom = ce->entry_sp();
441 if (bottom != nullptr) {
442 values.describe(-1, bottom, "continuation entry");
443 }
444 }
445 }
446 }
447 #endif
448
449 #ifdef ASSERT
450 void Continuation::debug_verify_continuation(oop contOop) {
451 if (!VerifyContinuations) {
452 return;
453 }
454 assert(contOop != nullptr, "");
455 assert(oopDesc::is_oop(contOop), "");
456 ContinuationWrapper cont(contOop);
457
458 assert(oopDesc::is_oop_or_null(cont.tail()), "");
459 assert(cont.chunk_invariant(), "");
460
461 bool nonempty_chunk = false;
462 size_t max_size = 0;
463 int num_chunks = 0;
464 int num_frames = 0;
465 int num_interpreted_frames = 0;
466 int num_oops = 0;
467
468 for (stackChunkOop chunk = cont.tail(); chunk != nullptr; chunk = chunk->parent()) {
469 log_develop_trace(continuations)("debug_verify_continuation chunk %d", num_chunks);
470 chunk->verify(&max_size, &num_oops, &num_frames, &num_interpreted_frames);
471 if (!chunk->is_empty()) {
472 nonempty_chunk = true;
473 }
474 num_chunks++;
475 }
476
477 const bool is_empty = cont.is_empty();
478 assert(!nonempty_chunk || !is_empty, "");
479 assert(is_empty == (!nonempty_chunk && cont.last_frame().is_empty()), "");
480 }
481
482 void Continuation::print(oop continuation) { print_on(tty, continuation); }
483
484 void Continuation::print_on(outputStream* st, oop continuation) {
485 ContinuationWrapper cont(continuation);
486
487 st->print_cr("CONTINUATION: " PTR_FORMAT " done: %d",
488 continuation->identity_hash(), jdk_internal_vm_Continuation::done(continuation));
489 st->print_cr("CHUNKS:");
490 for (stackChunkOop chunk = cont.tail(); chunk != nullptr; chunk = chunk->parent()) {
491 st->print("* ");
492 chunk->print_on(true, st);
493 }
494 }
495 #endif // ASSERT
496
497
498 void continuations_init() { Continuations::init(); }
499
500 void Continuations::init() {
501 Continuation::init();
502 }
503
504 bool Continuations::enabled() {
505 return VMContinuations;
506 }
507
508 #define CC (char*) /*cast a literal from (const char*)*/
509 #define FN_PTR(f) CAST_FROM_FN_PTR(void*, &f)
510
511 static JNINativeMethod CONT_methods[] = {
512 {CC"pin", CC"()V", FN_PTR(CONT_pin)},
513 {CC"unpin", CC"()V", FN_PTR(CONT_unpin)},
514 {CC"isPinned0", CC"(Ljdk/internal/vm/ContinuationScope;)I", FN_PTR(CONT_isPinned0)},
515 };
516
517 void CONT_RegisterNativeMethods(JNIEnv *env, jclass cls) {
518 JavaThread* thread = JavaThread::current();
519 ThreadToNativeFromVM trans(thread);
520 int status = env->RegisterNatives(cls, CONT_methods, sizeof(CONT_methods)/sizeof(JNINativeMethod));
521 guarantee(status == JNI_OK, "register jdk.internal.vm.Continuation natives");
522 guarantee(!env->ExceptionCheck(), "register jdk.internal.vm.Continuation natives");
523 }