1 /*
   2  * Copyright (c) 1998, 2014, 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 "classfile/systemDictionary.hpp"
  27 #include "oops/oop.inline.hpp"
  28 #include "prims/jvmtiExport.hpp"
  29 #include "runtime/jniHandles.hpp"
  30 #include "runtime/mutexLocker.hpp"
  31 #include "runtime/thread.inline.hpp"
  32 
  33 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
  34 
  35 JNIHandleBlock* JNIHandles::_global_handles       = NULL;
  36 JNIHandleBlock* JNIHandles::_weak_global_handles  = NULL;
  37 oop             JNIHandles::_deleted_handle       = NULL;
  38 
  39 
  40 jobject JNIHandles::make_local(oop obj) {
  41   if (obj == NULL) {
  42     return NULL;                // ignore null handles
  43   } else {
  44     Thread* thread = Thread::current();
  45     assert(Universe::heap()->is_in_reserved(obj), "sanity check");
  46     return thread->active_handles()->allocate_handle(obj);
  47   }
  48 }
  49 
  50 
  51 // optimized versions
  52 
  53 jobject JNIHandles::make_local(Thread* thread, oop obj) {
  54   if (obj == NULL) {
  55     return NULL;                // ignore null handles
  56   } else {
  57     assert(Universe::heap()->is_in_reserved(obj), "sanity check");
  58     return thread->active_handles()->allocate_handle(obj);
  59   }
  60 }
  61 
  62 
  63 jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
  64   if (obj == NULL) {
  65     return NULL;                // ignore null handles
  66   } else {
  67     JavaThread* thread = JavaThread::thread_from_jni_environment(env);
  68     assert(Universe::heap()->is_in_reserved(obj), "sanity check");
  69     return thread->active_handles()->allocate_handle(obj);
  70   }
  71 }
  72 
  73 
  74 jobject JNIHandles::make_global(Handle obj) {
  75   assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
  76   jobject res = NULL;
  77   if (!obj.is_null()) {
  78     // ignore null handles
  79     MutexLocker ml(JNIGlobalHandle_lock);
  80     assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
  81     res = _global_handles->allocate_handle(obj());
  82   } else {
  83     CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
  84   }
  85 
  86   return res;
  87 }
  88 
  89 
  90 jobject JNIHandles::make_weak_global(Handle obj) {
  91   assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
  92   jobject res = NULL;
  93   if (!obj.is_null()) {
  94     // ignore null handles
  95     MutexLocker ml(JNIGlobalHandle_lock);
  96     assert(Universe::heap()->is_in_reserved(obj()), "sanity check");
  97     res = _weak_global_handles->allocate_handle(obj());
  98   } else {
  99     CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
 100   }
 101   return res;
 102 }
 103 
 104 
 105 void JNIHandles::destroy_global(jobject handle) {
 106   if (handle != NULL) {
 107     assert(is_global_handle(handle), "Invalid delete of global JNI handle");
 108     *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
 109   }
 110 }
 111 
 112 
 113 void JNIHandles::destroy_weak_global(jobject handle) {
 114   if (handle != NULL) {
 115     assert(!CheckJNICalls || is_weak_global_handle(handle), "Invalid delete of weak global JNI handle");
 116     *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
 117   }
 118 }
 119 
 120 
 121 void JNIHandles::oops_do(OopClosure* f) {
 122   f->do_oop(&_deleted_handle);
 123   _global_handles->oops_do(f);
 124 }
 125 
 126 
 127 void JNIHandles::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
 128   _weak_global_handles->weak_oops_do(is_alive, f);
 129 }
 130 
 131 
 132 void JNIHandles::initialize() {
 133   _global_handles      = JNIHandleBlock::allocate_block();
 134   _weak_global_handles = JNIHandleBlock::allocate_block();
 135   EXCEPTION_MARK;
 136   // We will never reach the CATCH below since Exceptions::_throw will cause
 137   // the VM to exit if an exception is thrown during initialization
 138   Klass* k      = SystemDictionary::Object_klass();
 139   _deleted_handle = InstanceKlass::cast(k)->allocate_instance(CATCH);
 140 }
 141 
 142 
 143 bool JNIHandles::is_local_handle(Thread* thread, jobject handle) {
 144   JNIHandleBlock* block = thread->active_handles();
 145 
 146   // Look back past possible native calls to jni_PushLocalFrame.
 147   while (block != NULL) {
 148     if (block->chain_contains(handle)) {
 149       return true;
 150     }
 151     block = block->pop_frame_link();
 152   }
 153   return false;
 154 }
 155 
 156 
 157 // Determine if the handle is somewhere in the current thread's stack.
 158 // We easily can't isolate any particular stack frame the handle might
 159 // come from, so we'll check the whole stack.
 160 
 161 bool JNIHandles::is_frame_handle(JavaThread* thr, jobject obj) {
 162   // If there is no java frame, then this must be top level code, such
 163   // as the java command executable, in which case, this type of handle
 164   // is not permitted.
 165   return (thr->has_last_Java_frame() &&
 166          (void*)obj < (void*)thr->stack_base() &&
 167          (void*)obj >= (void*)thr->last_Java_sp());
 168 }
 169 
 170 
 171 bool JNIHandles::is_global_handle(jobject handle) {
 172   return _global_handles->chain_contains(handle);
 173 }
 174 
 175 
 176 bool JNIHandles::is_weak_global_handle(jobject handle) {
 177   return _weak_global_handles->chain_contains(handle);
 178 }
 179 
 180 long JNIHandles::global_handle_memory_usage() {
 181   return _global_handles->memory_usage();
 182 }
 183 
 184 long JNIHandles::weak_global_handle_memory_usage() {
 185   return _weak_global_handles->memory_usage();
 186 }
 187 
 188 
 189 class AlwaysAliveClosure: public BoolObjectClosure {
 190 public:
 191   bool do_object_b(oop obj) { return true; }
 192 };
 193 
 194 class CountHandleClosure: public OopClosure {
 195 private:
 196   int _count;
 197 public:
 198   CountHandleClosure(): _count(0) {}
 199   virtual void do_oop(oop* unused) {
 200     _count++;
 201   }
 202   virtual void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
 203   int count() { return _count; }
 204 };
 205 
 206 // We assume this is called at a safepoint: no lock is needed.
 207 void JNIHandles::print_on(outputStream* st) {
 208   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
 209   assert(_global_handles != NULL && _weak_global_handles != NULL,
 210          "JNIHandles not initialized");
 211 
 212   CountHandleClosure global_handle_count;
 213   AlwaysAliveClosure always_alive;
 214   oops_do(&global_handle_count);
 215   weak_oops_do(&always_alive, &global_handle_count);
 216 
 217   st->print_cr("JNI global references: %d", global_handle_count.count());
 218   st->cr();
 219   st->flush();
 220 }
 221 
 222 class VerifyHandleClosure: public OopClosure {
 223 public:
 224   virtual void do_oop(oop* root) {
 225     (*root)->verify();
 226   }
 227   virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
 228 };
 229 
 230 void JNIHandles::verify() {
 231   VerifyHandleClosure verify_handle;
 232   AlwaysAliveClosure always_alive;
 233 
 234   oops_do(&verify_handle);
 235   weak_oops_do(&always_alive, &verify_handle);
 236 }
 237 
 238 
 239 
 240 void jni_handles_init() {
 241   JNIHandles::initialize();
 242 }
 243 
 244 
 245 int             JNIHandleBlock::_blocks_allocated     = 0;
 246 JNIHandleBlock* JNIHandleBlock::_block_free_list      = NULL;
 247 #ifndef PRODUCT
 248 JNIHandleBlock* JNIHandleBlock::_block_list           = NULL;
 249 #endif
 250 
 251 
 252 void JNIHandleBlock::zap() {
 253   // Zap block values
 254   _top  = 0;
 255   for (int index = 0; index < block_size_in_oops; index++) {
 256     _handles[index] = badJNIHandle;
 257   }
 258 }
 259 
 260 JNIHandleBlock* JNIHandleBlock::allocate_block(Thread* thread)  {
 261   assert(thread == NULL || thread == Thread::current(), "sanity check");
 262   JNIHandleBlock* block;
 263   // Check the thread-local free list for a block so we don't
 264   // have to acquire a mutex.
 265   if (thread != NULL && thread->free_handle_block() != NULL) {
 266     block = thread->free_handle_block();
 267     thread->set_free_handle_block(block->_next);
 268   }
 269   else {
 270     // locking with safepoint checking introduces a potential deadlock:
 271     // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
 272     // - another would hold Threads_lock (jni_AttachCurrentThread) and then
 273     //   JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
 274     MutexLockerEx ml(JNIHandleBlockFreeList_lock,
 275                      Mutex::_no_safepoint_check_flag);
 276     if (_block_free_list == NULL) {
 277       // Allocate new block
 278       block = new JNIHandleBlock();
 279       _blocks_allocated++;
 280       if (TraceJNIHandleAllocation) {
 281         tty->print_cr("JNIHandleBlock " INTPTR_FORMAT " allocated (%d total blocks)",
 282                       block, _blocks_allocated);
 283       }
 284       if (ZapJNIHandleArea) block->zap();
 285       #ifndef PRODUCT
 286       // Link new block to list of all allocated blocks
 287       block->_block_list_link = _block_list;
 288       _block_list = block;
 289       #endif
 290     } else {
 291       // Get block from free list
 292       block = _block_free_list;
 293       _block_free_list = _block_free_list->_next;
 294     }
 295   }
 296   block->_top  = 0;
 297   block->_next = NULL;
 298   block->_pop_frame_link = NULL;
 299   // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
 300   debug_only(block->_last = NULL);
 301   debug_only(block->_free_list = NULL);
 302   debug_only(block->_allocate_before_rebuild = -1);
 303   return block;
 304 }
 305 
 306 
 307 void JNIHandleBlock::release_block(JNIHandleBlock* block, Thread* thread) {
 308   assert(thread == NULL || thread == Thread::current(), "sanity check");
 309   JNIHandleBlock* pop_frame_link = block->pop_frame_link();
 310   // Put returned block at the beginning of the thread-local free list.
 311   // Note that if thread == NULL, we use it as an implicit argument that
 312   // we _don't_ want the block to be kept on the free_handle_block.
 313   // See for instance JavaThread::exit().
 314   if (thread != NULL ) {
 315     if (ZapJNIHandleArea) block->zap();
 316     JNIHandleBlock* freelist = thread->free_handle_block();
 317     block->_pop_frame_link = NULL;
 318     thread->set_free_handle_block(block);
 319 
 320     // Add original freelist to end of chain
 321     if ( freelist != NULL ) {
 322       while ( block->_next != NULL ) block = block->_next;
 323       block->_next = freelist;
 324     }
 325     block = NULL;
 326   }
 327   if (block != NULL) {
 328     // Return blocks to free list
 329     // locking with safepoint checking introduces a potential deadlock:
 330     // - we would hold JNIHandleBlockFreeList_lock and then Threads_lock
 331     // - another would hold Threads_lock (jni_AttachCurrentThread) and then
 332     //   JNIHandleBlockFreeList_lock (JNIHandleBlock::allocate_block)
 333     MutexLockerEx ml(JNIHandleBlockFreeList_lock,
 334                      Mutex::_no_safepoint_check_flag);
 335     while (block != NULL) {
 336       if (ZapJNIHandleArea) block->zap();
 337       JNIHandleBlock* next = block->_next;
 338       block->_next = _block_free_list;
 339       _block_free_list = block;
 340       block = next;
 341     }
 342   }
 343   if (pop_frame_link != NULL) {
 344     // As a sanity check we release blocks pointed to by the pop_frame_link.
 345     // This should never happen (only if PopLocalFrame is not called the
 346     // correct number of times).
 347     release_block(pop_frame_link, thread);
 348   }
 349 }
 350 
 351 
 352 void JNIHandleBlock::oops_do(OopClosure* f) {
 353   JNIHandleBlock* current_chain = this;
 354   // Iterate over chain of blocks, followed by chains linked through the
 355   // pop frame links.
 356   while (current_chain != NULL) {
 357     for (JNIHandleBlock* current = current_chain; current != NULL;
 358          current = current->_next) {
 359       assert(current == current_chain || current->pop_frame_link() == NULL,
 360         "only blocks first in chain should have pop frame link set");
 361       for (int index = 0; index < current->_top; index++) {
 362         oop* root = &(current->_handles)[index];
 363         oop value = *root;
 364         // traverse heap pointers only, not deleted handles or free list
 365         // pointers
 366         if (value != NULL && Universe::heap()->is_in_reserved(value)) {
 367           f->do_oop(root);
 368         }
 369       }
 370       // the next handle block is valid only if current block is full
 371       if (current->_top < block_size_in_oops) {
 372         break;
 373       }
 374     }
 375     current_chain = current_chain->pop_frame_link();
 376   }
 377 }
 378 
 379 
 380 void JNIHandleBlock::weak_oops_do(BoolObjectClosure* is_alive,
 381                                   OopClosure* f) {
 382   for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
 383     assert(current->pop_frame_link() == NULL,
 384       "blocks holding weak global JNI handles should not have pop frame link set");
 385     for (int index = 0; index < current->_top; index++) {
 386       oop* root = &(current->_handles)[index];
 387       oop value = *root;
 388       // traverse heap pointers only, not deleted handles or free list pointers
 389       if (value != NULL && Universe::heap()->is_in_reserved(value)) {
 390         if (is_alive->do_object_b(value)) {
 391           // The weakly referenced object is alive, update pointer
 392           f->do_oop(root);
 393         } else {
 394           // The weakly referenced object is not alive, clear the reference by storing NULL
 395           if (TraceReferenceGC) {
 396             tty->print_cr("Clearing JNI weak reference (" INTPTR_FORMAT ")", root);
 397           }
 398           *root = NULL;
 399         }
 400       }
 401     }
 402     // the next handle block is valid only if current block is full
 403     if (current->_top < block_size_in_oops) {
 404       break;
 405     }
 406   }
 407 
 408   /*
 409    * JVMTI data structures may also contain weak oops.  The iteration of them
 410    * is placed here so that we don't need to add it to each of the collectors.
 411    */
 412   JvmtiExport::weak_oops_do(is_alive, f);
 413 }
 414 
 415 
 416 jobject JNIHandleBlock::allocate_handle(oop obj) {
 417   assert(Universe::heap()->is_in_reserved(obj), "sanity check");
 418   if (_top == 0) {
 419     // This is the first allocation or the initial block got zapped when
 420     // entering a native function. If we have any following blocks they are
 421     // not valid anymore.
 422     for (JNIHandleBlock* current = _next; current != NULL;
 423          current = current->_next) {
 424       assert(current->_last == NULL, "only first block should have _last set");
 425       assert(current->_free_list == NULL,
 426              "only first block should have _free_list set");
 427       current->_top = 0;
 428       if (ZapJNIHandleArea) current->zap();
 429     }
 430     // Clear initial block
 431     _free_list = NULL;
 432     _allocate_before_rebuild = 0;
 433     _last = this;
 434     if (ZapJNIHandleArea) zap();
 435   }
 436 
 437   // Try last block
 438   if (_last->_top < block_size_in_oops) {
 439     oop* handle = &(_last->_handles)[_last->_top++];
 440     *handle = obj;
 441     return (jobject) handle;
 442   }
 443 
 444   // Try free list
 445   if (_free_list != NULL) {
 446     oop* handle = _free_list;
 447     _free_list = (oop*) *_free_list;
 448     *handle = obj;
 449     return (jobject) handle;
 450   }
 451   // Check if unused block follow last
 452   if (_last->_next != NULL) {
 453     // update last and retry
 454     _last = _last->_next;
 455     return allocate_handle(obj);
 456   }
 457 
 458   // No space available, we have to rebuild free list or expand
 459   if (_allocate_before_rebuild == 0) {
 460       rebuild_free_list();        // updates _allocate_before_rebuild counter
 461   } else {
 462     // Append new block
 463     Thread* thread = Thread::current();
 464     Handle obj_handle(thread, obj);
 465     // This can block, so we need to preserve obj accross call.
 466     _last->_next = JNIHandleBlock::allocate_block(thread);
 467     _last = _last->_next;
 468     _allocate_before_rebuild--;
 469     obj = obj_handle();
 470   }
 471   return allocate_handle(obj);  // retry
 472 }
 473 
 474 
 475 void JNIHandleBlock::rebuild_free_list() {
 476   assert(_allocate_before_rebuild == 0 && _free_list == NULL, "just checking");
 477   int free = 0;
 478   int blocks = 0;
 479   for (JNIHandleBlock* current = this; current != NULL; current = current->_next) {
 480     for (int index = 0; index < current->_top; index++) {
 481       oop* handle = &(current->_handles)[index];
 482       if (*handle ==  JNIHandles::deleted_handle()) {
 483         // this handle was cleared out by a delete call, reuse it
 484         *handle = (oop) _free_list;
 485         _free_list = handle;
 486         free++;
 487       }
 488     }
 489     // we should not rebuild free list if there are unused handles at the end
 490     assert(current->_top == block_size_in_oops, "just checking");
 491     blocks++;
 492   }
 493   // Heuristic: if more than half of the handles are free we rebuild next time
 494   // as well, otherwise we append a corresponding number of new blocks before
 495   // attempting a free list rebuild again.
 496   int total = blocks * block_size_in_oops;
 497   int extra = total - 2*free;
 498   if (extra > 0) {
 499     // Not as many free handles as we would like - compute number of new blocks to append
 500     _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
 501   }
 502   if (TraceJNIHandleAllocation) {
 503     tty->print_cr("Rebuild free list JNIHandleBlock " INTPTR_FORMAT " blocks=%d used=%d free=%d add=%d",
 504       this, blocks, total-free, free, _allocate_before_rebuild);
 505   }
 506 }
 507 
 508 
 509 bool JNIHandleBlock::contains(jobject handle) const {
 510   return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
 511 }
 512 
 513 
 514 bool JNIHandleBlock::chain_contains(jobject handle) const {
 515   for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != NULL; current = current->_next) {
 516     if (current->contains(handle)) {
 517       return true;
 518     }
 519   }
 520   return false;
 521 }
 522 
 523 
 524 int JNIHandleBlock::length() const {
 525   int result = 1;
 526   for (JNIHandleBlock* current = _next; current != NULL; current = current->_next) {
 527     result++;
 528   }
 529   return result;
 530 }
 531 
 532 // This method is not thread-safe, i.e., must be called whule holding a lock on the
 533 // structure.
 534 long JNIHandleBlock::memory_usage() const {
 535   return length() * sizeof(JNIHandleBlock);
 536 }
 537 
 538 
 539 #ifndef PRODUCT
 540 
 541 bool JNIHandleBlock::any_contains(jobject handle) {
 542   for (JNIHandleBlock* current = _block_list; current != NULL; current = current->_block_list_link) {
 543     if (current->contains(handle)) {
 544       return true;
 545     }
 546   }
 547   return false;
 548 }
 549 
 550 void JNIHandleBlock::print_statistics() {
 551   int used_blocks = 0;
 552   int free_blocks = 0;
 553   int used_handles = 0;
 554   int free_handles = 0;
 555   JNIHandleBlock* block = _block_list;
 556   while (block != NULL) {
 557     if (block->_top > 0) {
 558       used_blocks++;
 559     } else {
 560       free_blocks++;
 561     }
 562     used_handles += block->_top;
 563     free_handles += (block_size_in_oops - block->_top);
 564     block = block->_block_list_link;
 565   }
 566   tty->print_cr("JNIHandleBlocks statistics");
 567   tty->print_cr("- blocks allocated: %d", used_blocks + free_blocks);
 568   tty->print_cr("- blocks in use:    %d", used_blocks);
 569   tty->print_cr("- blocks free:      %d", free_blocks);
 570   tty->print_cr("- handles in use:   %d", used_handles);
 571   tty->print_cr("- handles free:     %d", free_handles);
 572 }
 573 
 574 #endif