1 /*
2 * Copyright (c) 1998, 2023, 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 "gc/shared/collectedHeap.hpp"
27 #include "gc/shared/oopStorage.inline.hpp"
28 #include "gc/shared/oopStorageSet.hpp"
29 #include "logging/log.hpp"
30 #include "memory/iterator.hpp"
31 #include "memory/universe.hpp"
32 #include "oops/access.inline.hpp"
33 #include "oops/oop.inline.hpp"
34 #include "runtime/handles.inline.hpp"
35 #include "runtime/javaThread.inline.hpp"
36 #include "runtime/jniHandles.inline.hpp"
37 #include "runtime/mutexLocker.hpp"
38 #include "utilities/align.hpp"
39 #include "utilities/debug.hpp"
40
41 OopStorage* JNIHandles::global_handles() {
42 return _global_handles;
43 }
44
45 OopStorage* JNIHandles::weak_global_handles() {
46 return _weak_global_handles;
47 }
48
49 // Serviceability agent support.
50 OopStorage* JNIHandles::_global_handles = nullptr;
51 OopStorage* JNIHandles::_weak_global_handles = nullptr;
52
53 void jni_handles_init() {
54 JNIHandles::_global_handles = OopStorageSet::create_strong("JNI Global", mtInternal);
55 JNIHandles::_weak_global_handles = OopStorageSet::create_weak("JNI Weak", mtInternal);
56 }
57
58 jobject JNIHandles::make_local(oop obj) {
59 return make_local(JavaThread::current(), obj);
60 }
61
62 // Used by NewLocalRef which requires null on out-of-memory
63 jobject JNIHandles::make_local(JavaThread* thread, oop obj, AllocFailType alloc_failmode) {
64 if (obj == nullptr) {
65 return nullptr; // ignore null handles
66 } else {
67 assert(oopDesc::is_oop(obj), "not an oop");
68 assert(!current_thread_in_native(), "must not be in native");
69 STATIC_ASSERT(TypeTag::local == 0);
70 return thread->active_handles()->allocate_handle(thread, obj, alloc_failmode);
71 }
72 }
73
74 static void report_handle_allocation_failure(AllocFailType alloc_failmode,
75 const char* handle_kind) {
76 if (alloc_failmode == AllocFailStrategy::EXIT_OOM) {
77 // Fake size value, since we don't know the min allocation size here.
78 vm_exit_out_of_memory(sizeof(oop), OOM_MALLOC_ERROR,
79 "Cannot create %s JNI handle", handle_kind);
80 } else {
81 assert(alloc_failmode == AllocFailStrategy::RETURN_NULL, "invariant");
82 }
83 }
84
85 jobject JNIHandles::make_global(Handle obj, AllocFailType alloc_failmode) {
86 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
87 assert(!current_thread_in_native(), "must not be in native");
88 jobject res = nullptr;
89 if (!obj.is_null()) {
90 // ignore null handles
91 assert(oopDesc::is_oop(obj()), "not an oop");
92 oop* ptr = global_handles()->allocate();
93 // Return null on allocation failure.
94 if (ptr != nullptr) {
95 assert(NativeAccess<AS_NO_KEEPALIVE>::oop_load(ptr) == oop(nullptr), "invariant");
96 NativeAccess<>::oop_store(ptr, obj());
97 char* tptr = reinterpret_cast<char*>(ptr) + TypeTag::global;
98 res = reinterpret_cast<jobject>(tptr);
99 } else {
100 report_handle_allocation_failure(alloc_failmode, "global");
101 }
102 }
103
104 return res;
105 }
106
107 jweak JNIHandles::make_weak_global(Handle obj, AllocFailType alloc_failmode) {
108 assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
109 assert(!current_thread_in_native(), "must not be in native");
110 jweak res = nullptr;
111 if (!obj.is_null()) {
112 // ignore null handles
113 assert(oopDesc::is_oop(obj()), "not an oop");
114 oop* ptr = weak_global_handles()->allocate();
115 // Return nullptr on allocation failure.
116 if (ptr != nullptr) {
117 assert(NativeAccess<AS_NO_KEEPALIVE>::oop_load(ptr) == oop(nullptr), "invariant");
118 NativeAccess<ON_PHANTOM_OOP_REF>::oop_store(ptr, obj());
119 char* tptr = reinterpret_cast<char*>(ptr) + TypeTag::weak_global;
120 res = reinterpret_cast<jweak>(tptr);
121 } else {
122 report_handle_allocation_failure(alloc_failmode, "weak global");
123 }
124 }
125 return res;
126 }
127
128 // Resolve some erroneous cases to null, rather than treating them as
129 // possibly unchecked errors. In particular, deleted handles are
130 // treated as null (though a deleted and later reallocated handle
131 // isn't detected).
132 oop JNIHandles::resolve_external_guard(jobject handle) {
133 oop result = nullptr;
134 if (handle != nullptr) {
135 result = resolve_impl<DECORATORS_NONE, true /* external_guard */>(handle);
136 }
137 return result;
138 }
139
140 bool JNIHandles::is_weak_global_cleared(jweak handle) {
141 assert(handle != nullptr, "precondition");
142 oop* oop_ptr = weak_global_ptr(handle);
143 oop value = NativeAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(oop_ptr);
144 return value == nullptr;
145 }
146
147 void JNIHandles::destroy_global(jobject handle) {
148 if (handle != nullptr) {
149 oop* oop_ptr = global_ptr(handle);
150 NativeAccess<>::oop_store(oop_ptr, (oop)nullptr);
151 global_handles()->release(oop_ptr);
152 }
153 }
154
155
156 void JNIHandles::destroy_weak_global(jweak handle) {
157 if (handle != nullptr) {
158 oop* oop_ptr = weak_global_ptr(handle);
159 NativeAccess<ON_PHANTOM_OOP_REF>::oop_store(oop_ptr, (oop)nullptr);
160 weak_global_handles()->release(oop_ptr);
161 }
162 }
163
164
165 void JNIHandles::oops_do(OopClosure* f) {
166 global_handles()->oops_do(f);
167 }
168
169
170 void JNIHandles::weak_oops_do(OopClosure* f) {
171 weak_global_handles()->weak_oops_do(f);
172 }
173
174 bool JNIHandles::is_global_storage(const OopStorage* storage) {
175 return _global_handles == storage;
176 }
177
178 inline bool is_storage_handle(const OopStorage* storage, const oop* ptr) {
179 return storage->allocation_status(ptr) == OopStorage::ALLOCATED_ENTRY;
180 }
181
182
183 jobjectRefType JNIHandles::handle_type(JavaThread* thread, jobject handle) {
184 assert(handle != nullptr, "precondition");
185 jobjectRefType result = JNIInvalidRefType;
186 if (is_weak_global_tagged(handle)) {
187 if (is_storage_handle(weak_global_handles(), weak_global_ptr(handle))) {
188 result = JNIWeakGlobalRefType;
189 }
190 } else if (is_global_tagged(handle)) {
191 switch (global_handles()->allocation_status(global_ptr(handle))) {
192 case OopStorage::ALLOCATED_ENTRY:
193 result = JNIGlobalRefType;
194 break;
195
196 case OopStorage::UNALLOCATED_ENTRY:
197 break; // Invalid global handle
198
199 default:
200 ShouldNotReachHere();
201 }
202 } else if (is_local_handle(thread, handle) || is_frame_handle(thread, handle)) {
203 // Not in global storage. Might be a local handle.
204 result = JNILocalRefType;
205 }
206 return result;
207 }
208
209
210 bool JNIHandles::is_local_handle(JavaThread* thread, jobject handle) {
211 assert(handle != nullptr, "precondition");
212 JNIHandleBlock* block = thread->active_handles();
213
214 // Look back past possible native calls to jni_PushLocalFrame.
215 while (block != nullptr) {
216 if (block->chain_contains(handle)) {
217 return true;
218 }
219 block = block->pop_frame_link();
220 }
221 return false;
222 }
223
224
225 // Determine if the handle is somewhere in the current thread's stack.
226 // We easily can't isolate any particular stack frame the handle might
227 // come from, so we'll check the whole stack.
228
229 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject handle) {
230 assert(handle != nullptr, "precondition");
231 // If there is no java frame, then this must be top level code, such
232 // as the java command executable, in which case, this type of handle
233 // is not permitted.
234 return (thr->has_last_Java_frame() &&
235 thr->is_in_stack_range_incl((address)handle, (address)thr->last_Java_sp()));
236 }
237
238
239 bool JNIHandles::is_global_handle(jobject handle) {
240 assert(handle != nullptr, "precondition");
241 return is_global_tagged(handle) && is_storage_handle(global_handles(), global_ptr(handle));
242 }
243
244
245 bool JNIHandles::is_weak_global_handle(jobject handle) {
246 assert(handle != nullptr, "precondition");
247 return is_weak_global_tagged(handle) && is_storage_handle(weak_global_handles(), weak_global_ptr(handle));
248 }
249
250 // We assume this is called at a safepoint: no lock is needed.
251 void JNIHandles::print_on(outputStream* st) {
252 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
253
254 st->print_cr("JNI global refs: " SIZE_FORMAT ", weak refs: " SIZE_FORMAT,
255 global_handles()->allocation_count(),
256 weak_global_handles()->allocation_count());
257 st->cr();
258 st->flush();
259 }
260
261 void JNIHandles::print() { print_on(tty); }
262
263 class VerifyJNIHandles: public OopClosure {
264 public:
265 virtual void do_oop(oop* root) {
266 guarantee(oopDesc::is_oop_or_null(RawAccess<>::oop_load(root)), "Invalid oop");
267 }
268 virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
269 };
270
271 void JNIHandles::verify() {
272 VerifyJNIHandles verify_handle;
273
274 oops_do(&verify_handle);
275 weak_oops_do(&verify_handle);
276 }
277
278 // This method is implemented here to avoid circular includes between
279 // jniHandles.hpp and thread.hpp.
280 bool JNIHandles::current_thread_in_native() {
281 Thread* thread = Thread::current();
282 return (thread->is_Java_thread() &&
283 JavaThread::cast(thread)->thread_state() == _thread_in_native);
284 }
285
286 int JNIHandleBlock::_blocks_allocated = 0;
287
288 static inline bool is_tagged_free_list(uintptr_t value) {
289 return (value & 1u) != 0;
290 }
291
292 static inline uintptr_t tag_free_list(uintptr_t value) {
293 return value | 1u;
294 }
295
296 static inline uintptr_t untag_free_list(uintptr_t value) {
297 return value & ~(uintptr_t)1u;
298 }
299
300 // There is a freelist of handles running through the JNIHandleBlock
301 // with a tagged next pointer, distinguishing these next pointers from
302 // oops. The freelist handling currently relies on the size of oops
303 // being the same as a native pointer. If this ever changes, then
304 // this freelist handling must change too.
305 STATIC_ASSERT(sizeof(oop) == sizeof(uintptr_t));
306
307 #ifdef ASSERT
308 void JNIHandleBlock::zap() {
309 // Zap block values
310 _top = 0;
311 for (int index = 0; index < block_size_in_oops; index++) {
312 // NOT using Access here; just bare clobbering to null, since the
313 // block no longer contains valid oops.
314 _handles[index] = 0;
315 }
316 }
317 #endif // ASSERT
318
319 JNIHandleBlock* JNIHandleBlock::allocate_block(JavaThread* thread, AllocFailType alloc_failmode) {
320 // The VM thread can allocate a handle block in behalf of another thread during a safepoint.
321 assert(thread == nullptr || thread == Thread::current() || SafepointSynchronize::is_at_safepoint(),
322 "sanity check");
323 JNIHandleBlock* block;
324 // Check the thread-local free list for a block so we don't
325 // have to acquire a mutex.
326 if (thread != nullptr && thread->free_handle_block() != nullptr) {
327 block = thread->free_handle_block();
328 thread->set_free_handle_block(block->_next);
329 } else {
330 // Allocate new block
331 if (alloc_failmode == AllocFailStrategy::RETURN_NULL) {
332 block = new (std::nothrow) JNIHandleBlock();
333 if (block == nullptr) {
334 return nullptr;
335 }
336 } else {
337 block = new JNIHandleBlock();
338 }
339 Atomic::inc(&_blocks_allocated);
340 block->zap();
341 }
342 block->_top = 0;
343 block->_next = nullptr;
344 block->_pop_frame_link = nullptr;
345 // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
346 debug_only(block->_last = nullptr);
347 debug_only(block->_free_list = nullptr);
348 debug_only(block->_allocate_before_rebuild = -1);
349 return block;
350 }
351
352
353 void JNIHandleBlock::release_block(JNIHandleBlock* block, JavaThread* thread) {
354 assert(thread == nullptr || thread == Thread::current(), "sanity check");
355 JNIHandleBlock* pop_frame_link = block->pop_frame_link();
356 // Put returned block at the beginning of the thread-local free list.
357 // Note that if thread == nullptr, we use it as an implicit argument that
358 // we _don't_ want the block to be kept on the free_handle_block.
359 // See for instance JavaThread::exit().
360 if (thread != nullptr ) {
361 block->zap();
362 JNIHandleBlock* freelist = thread->free_handle_block();
363 block->_pop_frame_link = nullptr;
364 thread->set_free_handle_block(block);
365
366 // Add original freelist to end of chain
367 if ( freelist != nullptr ) {
368 while ( block->_next != nullptr ) block = block->_next;
369 block->_next = freelist;
370 }
371 block = nullptr;
372 } else {
373 DEBUG_ONLY(block->set_pop_frame_link(nullptr));
374 while (block != nullptr) {
375 JNIHandleBlock* next = block->_next;
376 Atomic::dec(&_blocks_allocated);
377 assert(block->pop_frame_link() == nullptr, "pop_frame_link should be null");
378 delete block;
379 block = next;
380 }
381 }
382 if (pop_frame_link != nullptr) {
383 // As a sanity check we release blocks pointed to by the pop_frame_link.
384 // This should never happen (only if PopLocalFrame is not called the
385 // correct number of times).
386 release_block(pop_frame_link, thread);
387 }
388 }
389
390
391 void JNIHandleBlock::oops_do(OopClosure* f) {
392 JNIHandleBlock* current_chain = this;
393 // Iterate over chain of blocks, followed by chains linked through the
394 // pop frame links.
395 while (current_chain != nullptr) {
396 for (JNIHandleBlock* current = current_chain; current != nullptr;
397 current = current->_next) {
398 assert(current == current_chain || current->pop_frame_link() == nullptr,
399 "only blocks first in chain should have pop frame link set");
400 for (int index = 0; index < current->_top; index++) {
401 uintptr_t* addr = &(current->_handles)[index];
402 uintptr_t value = *addr;
403 // traverse heap pointers only, not deleted handles or free list
404 // pointers
405 if (value != 0 && !is_tagged_free_list(value)) {
406 oop* root = (oop*)addr;
407 f->do_oop(root);
408 }
409 }
410 // the next handle block is valid only if current block is full
411 if (current->_top < block_size_in_oops) {
412 break;
413 }
414 }
415 current_chain = current_chain->pop_frame_link();
416 }
417 }
418
419
420 jobject JNIHandleBlock::allocate_handle(JavaThread* caller, oop obj, AllocFailType alloc_failmode) {
421 assert(Universe::heap()->is_in(obj), "sanity check");
422 if (_top == 0) {
423 // This is the first allocation or the initial block got zapped when
424 // entering a native function. If we have any following blocks they are
425 // not valid anymore.
426 for (JNIHandleBlock* current = _next; current != nullptr;
427 current = current->_next) {
428 assert(current->_last == nullptr, "only first block should have _last set");
429 assert(current->_free_list == nullptr,
430 "only first block should have _free_list set");
431 if (current->_top == 0) {
432 // All blocks after the first clear trailing block are already cleared.
433 #ifdef ASSERT
434 for (current = current->_next; current != nullptr; current = current->_next) {
435 assert(current->_top == 0, "trailing blocks must already be cleared");
436 }
437 #endif
438 break;
439 }
440 current->_top = 0;
441 current->zap();
442 }
443 // Clear initial block
444 _free_list = nullptr;
445 _allocate_before_rebuild = 0;
446 _last = this;
447 zap();
448 }
449
450 // Try last block
451 if (_last->_top < block_size_in_oops) {
452 oop* handle = (oop*)&(_last->_handles)[_last->_top++];
453 *handle = obj;
454 return (jobject) handle;
455 }
456
457 // Try free list
458 if (_free_list != nullptr) {
459 oop* handle = (oop*)_free_list;
460 _free_list = (uintptr_t*) untag_free_list(*_free_list);
461 *handle = obj;
462 return (jobject) handle;
463 }
464 // Check if unused block follow last
465 if (_last->_next != nullptr) {
466 // update last and retry
467 _last = _last->_next;
468 return allocate_handle(caller, obj, alloc_failmode);
469 }
470
471 // No space available, we have to rebuild free list or expand
472 if (_allocate_before_rebuild == 0) {
473 rebuild_free_list(); // updates _allocate_before_rebuild counter
474 } else {
475 _last->_next = JNIHandleBlock::allocate_block(caller, alloc_failmode);
476 if (_last->_next == nullptr) {
477 return nullptr;
478 }
479 _last = _last->_next;
480 _allocate_before_rebuild--;
481 }
482 return allocate_handle(caller, obj, alloc_failmode); // retry
483 }
484
485 void JNIHandleBlock::rebuild_free_list() {
486 assert(_allocate_before_rebuild == 0 && _free_list == nullptr, "just checking");
487 int free = 0;
488 int blocks = 0;
489 for (JNIHandleBlock* current = this; current != nullptr; current = current->_next) {
490 for (int index = 0; index < current->_top; index++) {
491 uintptr_t* handle = &(current->_handles)[index];
492 if (*handle == 0) {
493 // this handle was cleared out by a delete call, reuse it
494 *handle = _free_list == nullptr ? 0 : tag_free_list((uintptr_t)_free_list);
495 _free_list = handle;
496 free++;
497 }
498 }
499 // we should not rebuild free list if there are unused handles at the end
500 assert(current->_top == block_size_in_oops, "just checking");
501 blocks++;
502 }
503 // Heuristic: if more than half of the handles are free we rebuild next time
504 // as well, otherwise we append a corresponding number of new blocks before
505 // attempting a free list rebuild again.
506 int total = blocks * block_size_in_oops;
507 int extra = total - 2*free;
508 if (extra > 0) {
509 // Not as many free handles as we would like - compute number of new blocks to append
510 _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
511 }
512 }
513
514
515 bool JNIHandleBlock::contains(jobject handle) const {
516 return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
517 }
518
519
520 bool JNIHandleBlock::chain_contains(jobject handle) const {
521 for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != nullptr; current = current->_next) {
522 if (current->contains(handle)) {
523 return true;
524 }
525 }
526 return false;
527 }