src/hotspot/share/runtime/jniHandles.cpp

/*
 * Copyright (c) 1998, 2023, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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#include "precompiled.hpp"
#include "gc/shared/collectedHeap.hpp"
#include "gc/shared/oopStorage.inline.hpp"
#include "gc/shared/oopStorageSet.hpp"
#include "logging/log.hpp"
#include "memory/iterator.hpp"
#include "memory/universe.hpp"
#include "oops/access.inline.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/javaThread.inline.hpp"
#include "runtime/jniHandles.inline.hpp"
#include "runtime/mutexLocker.hpp"
#include "utilities/align.hpp"
#include "utilities/debug.hpp"

OopStorage* JNIHandles::global_handles() {
  return _global_handles;
}

OopStorage* JNIHandles::weak_global_handles() {
  return _weak_global_handles;
}

// Serviceability agent support.
OopStorage* JNIHandles::_global_handles = nullptr;
OopStorage* JNIHandles::_weak_global_handles = nullptr;

void jni_handles_init() {
  JNIHandles::_global_handles = OopStorageSet::create_strong("JNI Global", mtInternal);
  JNIHandles::_weak_global_handles = OopStorageSet::create_weak("JNI Weak", mtInternal);
}

jobject JNIHandles::make_local(oop obj) {
  return make_local(JavaThread::current(), obj);
}

// Used by NewLocalRef which requires null on out-of-memory
jobject JNIHandles::make_local(JavaThread* thread, oop obj, AllocFailType alloc_failmode) {
  if (obj == nullptr) {
    return nullptr;                // ignore null handles
  } else {
    assert(oopDesc::is_oop(obj), "not an oop");
    assert(!current_thread_in_native(), "must not be in native");
    STATIC_ASSERT(TypeTag::local == 0);
    return thread->active_handles()->allocate_handle(thread, obj, alloc_failmode);
  }
}

static void report_handle_allocation_failure(AllocFailType alloc_failmode,
                                             const char* handle_kind) {
  if (alloc_failmode == AllocFailStrategy::EXIT_OOM) {
    // Fake size value, since we don't know the min allocation size here.
    vm_exit_out_of_memory(sizeof(oop), OOM_MALLOC_ERROR,
                          "Cannot create %s JNI handle", handle_kind);
  } else {
    assert(alloc_failmode == AllocFailStrategy::RETURN_NULL, "invariant");
  }
}

jobject JNIHandles::make_global(Handle obj, AllocFailType alloc_failmode) {
  assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
  assert(!current_thread_in_native(), "must not be in native");
  jobject res = nullptr;
  if (!obj.is_null()) {
    // ignore null handles
    assert(oopDesc::is_oop(obj()), "not an oop");
    oop* ptr = global_handles()->allocate();
    // Return null on allocation failure.
    if (ptr != nullptr) {
      assert(NativeAccess<AS_NO_KEEPALIVE>::oop_load(ptr) == oop(nullptr), "invariant");
      NativeAccess<>::oop_store(ptr, obj());
      char* tptr = reinterpret_cast<char*>(ptr) + TypeTag::global;
      res = reinterpret_cast<jobject>(tptr);
    } else {
      report_handle_allocation_failure(alloc_failmode, "global");
    }
  }

  return res;
}

jweak JNIHandles::make_weak_global(Handle obj, AllocFailType alloc_failmode) {
  assert(!Universe::heap()->is_gc_active(), "can't extend the root set during GC");
  assert(!current_thread_in_native(), "must not be in native");
  jweak res = nullptr;
  if (!obj.is_null()) {
    // ignore null handles
    assert(oopDesc::is_oop(obj()), "not an oop");
    oop* ptr = weak_global_handles()->allocate();
    // Return nullptr on allocation failure.
    if (ptr != nullptr) {
      assert(NativeAccess<AS_NO_KEEPALIVE>::oop_load(ptr) == oop(nullptr), "invariant");
      NativeAccess<ON_PHANTOM_OOP_REF>::oop_store(ptr, obj());
      char* tptr = reinterpret_cast<char*>(ptr) + TypeTag::weak_global;
      res = reinterpret_cast<jweak>(tptr);
    } else {
      report_handle_allocation_failure(alloc_failmode, "weak global");
    }
  }
  return res;
}

// Resolve some erroneous cases to null, rather than treating them as
// possibly unchecked errors.  In particular, deleted handles are
// treated as null (though a deleted and later reallocated handle
// isn't detected).
oop JNIHandles::resolve_external_guard(jobject handle) {
  oop result = nullptr;
  if (handle != nullptr) {
    result = resolve_impl<DECORATORS_NONE, true /* external_guard */>(handle);
  }
  return result;
}

bool JNIHandles::is_weak_global_cleared(jweak handle) {
  assert(handle != nullptr, "precondition");
  oop* oop_ptr = weak_global_ptr(handle);
  oop value = NativeAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(oop_ptr);
  return value == nullptr;
}

void JNIHandles::destroy_global(jobject handle) {
  if (handle != nullptr) {
    oop* oop_ptr = global_ptr(handle);
    NativeAccess<>::oop_store(oop_ptr, (oop)nullptr);
    global_handles()->release(oop_ptr);
  }
}


void JNIHandles::destroy_weak_global(jweak handle) {
  if (handle != nullptr) {
    oop* oop_ptr = weak_global_ptr(handle);
    NativeAccess<ON_PHANTOM_OOP_REF>::oop_store(oop_ptr, (oop)nullptr);
    weak_global_handles()->release(oop_ptr);
  }
}


void JNIHandles::oops_do(OopClosure* f) {
  global_handles()->oops_do(f);
}


void JNIHandles::weak_oops_do(OopClosure* f) {
  weak_global_handles()->weak_oops_do(f);
}

bool JNIHandles::is_global_storage(const OopStorage* storage) {
  return _global_handles == storage;
}

inline bool is_storage_handle(const OopStorage* storage, const oop* ptr) {
  return storage->allocation_status(ptr) == OopStorage::ALLOCATED_ENTRY;
}


jobjectRefType JNIHandles::handle_type(JavaThread* thread, jobject handle) {
  assert(handle != nullptr, "precondition");
  jobjectRefType result = JNIInvalidRefType;
  if (is_weak_global_tagged(handle)) {
    if (is_storage_handle(weak_global_handles(), weak_global_ptr(handle))) {
      result = JNIWeakGlobalRefType;
    }
  } else if (is_global_tagged(handle)) {
    switch (global_handles()->allocation_status(global_ptr(handle))) {
    case OopStorage::ALLOCATED_ENTRY:
      result = JNIGlobalRefType;
      break;

    case OopStorage::UNALLOCATED_ENTRY:
      break;                    // Invalid global handle

    default:
      ShouldNotReachHere();
    }
  } else if (is_local_handle(thread, handle) || is_frame_handle(thread, handle)) {
    // Not in global storage.  Might be a local handle.
    result = JNILocalRefType;
  }
  return result;
}


bool JNIHandles::is_local_handle(JavaThread* thread, jobject handle) {
  assert(handle != nullptr, "precondition");
  JNIHandleBlock* block = thread->active_handles();

  // Look back past possible native calls to jni_PushLocalFrame.
  while (block != nullptr) {
    if (block->chain_contains(handle)) {
      return true;
    }
    block = block->pop_frame_link();
  }
  return false;
}


// Determine if the handle is somewhere in the current thread's stack.
// We easily can't isolate any particular stack frame the handle might
// come from, so we'll check the whole stack.

bool JNIHandles::is_frame_handle(JavaThread* thr, jobject handle) {
  assert(handle != nullptr, "precondition");
  // If there is no java frame, then this must be top level code, such
  // as the java command executable, in which case, this type of handle
  // is not permitted.
  return (thr->has_last_Java_frame() &&
          thr->is_in_stack_range_incl((address)handle, (address)thr->last_Java_sp()));
}


bool JNIHandles::is_global_handle(jobject handle) {
  assert(handle != nullptr, "precondition");
  return is_global_tagged(handle) && is_storage_handle(global_handles(), global_ptr(handle));
}


bool JNIHandles::is_weak_global_handle(jobject handle) {
  assert(handle != nullptr, "precondition");
  return is_weak_global_tagged(handle) && is_storage_handle(weak_global_handles(), weak_global_ptr(handle));
}

// We assume this is called at a safepoint: no lock is needed.
void JNIHandles::print_on(outputStream* st) {
  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");

  st->print_cr("JNI global refs: " SIZE_FORMAT ", weak refs: " SIZE_FORMAT,
               global_handles()->allocation_count(),
               weak_global_handles()->allocation_count());
  st->cr();
  st->flush();
}

void JNIHandles::print() { print_on(tty); }

class VerifyJNIHandles: public OopClosure {
public:
  virtual void do_oop(oop* root) {
    guarantee(oopDesc::is_oop_or_null(RawAccess<>::oop_load(root)), "Invalid oop");
  }
  virtual void do_oop(narrowOop* root) { ShouldNotReachHere(); }
};

void JNIHandles::verify() {
  VerifyJNIHandles verify_handle;

  oops_do(&verify_handle);
  weak_oops_do(&verify_handle);
}

// This method is implemented here to avoid circular includes between
// jniHandles.hpp and thread.hpp.
bool JNIHandles::current_thread_in_native() {
  Thread* thread = Thread::current();
  return (thread->is_Java_thread() &&
          JavaThread::cast(thread)->thread_state() == _thread_in_native);
}

int JNIHandleBlock::_blocks_allocated = 0;

static inline bool is_tagged_free_list(uintptr_t value) {
  return (value & 1u) != 0;
}

static inline uintptr_t tag_free_list(uintptr_t value) {
  return value | 1u;
}

static inline uintptr_t untag_free_list(uintptr_t value) {
  return value & ~(uintptr_t)1u;
}

// There is a freelist of handles running through the JNIHandleBlock
// with a tagged next pointer, distinguishing these next pointers from
// oops. The freelist handling currently relies on the size of oops
// being the same as a native pointer. If this ever changes, then
// this freelist handling must change too.
STATIC_ASSERT(sizeof(oop) == sizeof(uintptr_t));

#ifdef ASSERT
void JNIHandleBlock::zap() {
  // Zap block values
  _top = 0;
  for (int index = 0; index < block_size_in_oops; index++) {
    // NOT using Access here; just bare clobbering to null, since the
    // block no longer contains valid oops.
    _handles[index] = 0;
  }
}
#endif // ASSERT

JNIHandleBlock* JNIHandleBlock::allocate_block(JavaThread* thread, AllocFailType alloc_failmode)  {
  // The VM thread can allocate a handle block in behalf of another thread during a safepoint.
  assert(thread == nullptr || thread == Thread::current() || SafepointSynchronize::is_at_safepoint(),
         "sanity check");
  JNIHandleBlock* block;
  // Check the thread-local free list for a block so we don't
  // have to acquire a mutex.
  if (thread != nullptr && thread->free_handle_block() != nullptr) {
    block = thread->free_handle_block();
    thread->set_free_handle_block(block->_next);
  } else {
    // Allocate new block
    if (alloc_failmode == AllocFailStrategy::RETURN_NULL) {
      block = new (std::nothrow) JNIHandleBlock();
      if (block == nullptr) {
        return nullptr;
      }
    } else {
      block = new JNIHandleBlock();
    }
    Atomic::inc(&_blocks_allocated);
    block->zap();
  }
  block->_top = 0;
  block->_next = nullptr;
  block->_pop_frame_link = nullptr;
  // _last, _free_list & _allocate_before_rebuild initialized in allocate_handle
  debug_only(block->_last = nullptr);
  debug_only(block->_free_list = nullptr);
  debug_only(block->_allocate_before_rebuild = -1);
  return block;
}


void JNIHandleBlock::release_block(JNIHandleBlock* block, JavaThread* thread) {
  assert(thread == nullptr || thread == Thread::current(), "sanity check");
  JNIHandleBlock* pop_frame_link = block->pop_frame_link();
  // Put returned block at the beginning of the thread-local free list.
  // Note that if thread == nullptr, we use it as an implicit argument that
  // we _don't_ want the block to be kept on the free_handle_block.
  // See for instance JavaThread::exit().
  if (thread != nullptr ) {
    block->zap();
    JNIHandleBlock* freelist = thread->free_handle_block();
    block->_pop_frame_link = nullptr;
    thread->set_free_handle_block(block);

    // Add original freelist to end of chain
    if ( freelist != nullptr ) {
      while ( block->_next != nullptr ) block = block->_next;
      block->_next = freelist;
    }
    block = nullptr;
  } else {
    DEBUG_ONLY(block->set_pop_frame_link(nullptr));
    while (block != nullptr) {
      JNIHandleBlock* next = block->_next;
      Atomic::dec(&_blocks_allocated);
      assert(block->pop_frame_link() == nullptr, "pop_frame_link should be null");
      delete block;
      block = next;
    }
  }
  if (pop_frame_link != nullptr) {
    // As a sanity check we release blocks pointed to by the pop_frame_link.
    // This should never happen (only if PopLocalFrame is not called the
    // correct number of times).
    release_block(pop_frame_link, thread);
  }
}


void JNIHandleBlock::oops_do(OopClosure* f) {
  JNIHandleBlock* current_chain = this;
  // Iterate over chain of blocks, followed by chains linked through the
  // pop frame links.
  while (current_chain != nullptr) {
    for (JNIHandleBlock* current = current_chain; current != nullptr;
         current = current->_next) {
      assert(current == current_chain || current->pop_frame_link() == nullptr,
        "only blocks first in chain should have pop frame link set");
      for (int index = 0; index < current->_top; index++) {
        uintptr_t* addr = &(current->_handles)[index];
        uintptr_t value = *addr;
        // traverse heap pointers only, not deleted handles or free list
        // pointers
        if (value != 0 && !is_tagged_free_list(value)) {
          oop* root = (oop*)addr;
          f->do_oop(root);
        }
      }
      // the next handle block is valid only if current block is full
      if (current->_top < block_size_in_oops) {
        break;
      }
    }
    current_chain = current_chain->pop_frame_link();
  }
}


jobject JNIHandleBlock::allocate_handle(JavaThread* caller, oop obj, AllocFailType alloc_failmode) {
  assert(Universe::heap()->is_in(obj), "sanity check");
  if (_top == 0) {
    // This is the first allocation or the initial block got zapped when
    // entering a native function. If we have any following blocks they are
    // not valid anymore.
    for (JNIHandleBlock* current = _next; current != nullptr;
         current = current->_next) {
      assert(current->_last == nullptr, "only first block should have _last set");
      assert(current->_free_list == nullptr,
             "only first block should have _free_list set");
      if (current->_top == 0) {
        // All blocks after the first clear trailing block are already cleared.
#ifdef ASSERT
        for (current = current->_next; current != nullptr; current = current->_next) {
          assert(current->_top == 0, "trailing blocks must already be cleared");
        }
#endif
        break;
      }
      current->_top = 0;
      current->zap();
    }
    // Clear initial block
    _free_list = nullptr;
    _allocate_before_rebuild = 0;
    _last = this;
    zap();
  }

  // Try last block
  if (_last->_top < block_size_in_oops) {
    oop* handle = (oop*)&(_last->_handles)[_last->_top++];
    *handle = obj;
    return (jobject) handle;
  }

  // Try free list
  if (_free_list != nullptr) {
    oop* handle = (oop*)_free_list;
    _free_list = (uintptr_t*) untag_free_list(*_free_list);
    *handle = obj;
    return (jobject) handle;
  }
  // Check if unused block follow last
  if (_last->_next != nullptr) {
    // update last and retry
    _last = _last->_next;
    return allocate_handle(caller, obj, alloc_failmode);
  }

  // No space available, we have to rebuild free list or expand
  if (_allocate_before_rebuild == 0) {
      rebuild_free_list();        // updates _allocate_before_rebuild counter
  } else {
    _last->_next = JNIHandleBlock::allocate_block(caller, alloc_failmode);
    if (_last->_next == nullptr) {
      return nullptr;
    }
    _last = _last->_next;
    _allocate_before_rebuild--;
  }
  return allocate_handle(caller, obj, alloc_failmode);  // retry
}

void JNIHandleBlock::rebuild_free_list() {
  assert(_allocate_before_rebuild == 0 && _free_list == nullptr, "just checking");
  int free = 0;
  int blocks = 0;
  for (JNIHandleBlock* current = this; current != nullptr; current = current->_next) {
    for (int index = 0; index < current->_top; index++) {
      uintptr_t* handle = &(current->_handles)[index];
      if (*handle == 0) {
        // this handle was cleared out by a delete call, reuse it
        *handle = _free_list == nullptr ? 0 : tag_free_list((uintptr_t)_free_list);
        _free_list = handle;
        free++;
      }
    }
    // we should not rebuild free list if there are unused handles at the end
    assert(current->_top == block_size_in_oops, "just checking");
    blocks++;
  }
  // Heuristic: if more than half of the handles are free we rebuild next time
  // as well, otherwise we append a corresponding number of new blocks before
  // attempting a free list rebuild again.
  int total = blocks * block_size_in_oops;
  int extra = total - 2*free;
  if (extra > 0) {
    // Not as many free handles as we would like - compute number of new blocks to append
    _allocate_before_rebuild = (extra + block_size_in_oops - 1) / block_size_in_oops;
  }
}


bool JNIHandleBlock::contains(jobject handle) const {
  return ((jobject)&_handles[0] <= handle && handle<(jobject)&_handles[_top]);
}


bool JNIHandleBlock::chain_contains(jobject handle) const {
  for (JNIHandleBlock* current = (JNIHandleBlock*) this; current != nullptr; current = current->_next) {
    if (current->contains(handle)) {
      return true;
    }
  }
  return false;
}