/*

 * Copyright (c) 2019, 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

#include "precompiled.hpp"

#include "jvmci/metadataHandleBlock.hpp"

MetadataHandleBlock* MetadataHandleBlock::_last = NULL;

intptr_t             MetadataHandleBlock::_free_list = 0;

int                  MetadataHandleBlock::_allocate_before_rebuild = 0;

jmetadata MetadataHandleBlock::allocate_metadata_handle(Metadata* obj) {

  assert(obj->is_valid() && obj->is_metadata(), "must be");

  if (_last == NULL) {

    // This is the first allocation.

    _last = this;

  }

  HandleRecord* handle = get_handle();

  if (handle != NULL) {

    handle->set_value(obj);

#ifdef METADATA_TRACK_NAMES

    handle->set_name(obj->print_value_string());

#endif

    return (jmetadata) handle;

  }

  // Check if unused block follow last

  if (_last->_next != NULL) {

    // update last and retry

    _last = _last->_next;

    return allocate_metadata_handle(obj);

  }

  // 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 {

    // Append new block

    // This can block, but the caller has a metadata handle around this object.

    _last->_next = allocate_block();

    _last = _last->_next;

    _allocate_before_rebuild--;

  }

  return allocate_metadata_handle(obj);  // retry

}

void MetadataHandleBlock::rebuild_free_list() {

  assert(_allocate_before_rebuild == 0 && _free_list == 0, "just checking");

  int free = 0;

  int blocks = 0;

  for (MetadataHandleBlock* current = this; current != NULL; current = current->_next) {

    for (int index = 0; index < current->_top; index++) {

      HandleRecord* handle = &(current->_handles)[index];

      if (handle->value() == NULL) {

        // this handle was cleared out by a delete call, reuse it

        chain_free_list(handle);

        free++;

      }

    }

    // we should not rebuild free list if there are unused handles at the end

    assert(current->_top == block_size_in_handles, "just checking");

    blocks++;

  }

  // Heuristic: if more than half of the handles are NOT 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_handles;

  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_handles - 1) / block_size_in_handles;

  }

}

void MetadataHandleBlock::metadata_do(void f(Metadata*)) {

  for (MetadataHandleBlock* current = this; current != NULL; current = current->_next) {

    for (int index = 0; index < current->_top; index++) {

      HandleRecord* root = &(current->_handles)[index];

      Metadata* value = root->value();

      // traverse heap pointers only, not deleted handles or free list

      // pointers

      if (value != NULL && ((intptr_t) value & ptr_tag) == 0) {

        assert(value->is_valid(), "invalid metadata %s", get_name(index));

        f(value);

      }

    }

    // the next handle block is valid only if current block is full

    if (current->_top < block_size_in_handles) {

      break;

    }

  }

}

// Visit any live metadata handles and clean them up.  Since clearing of these handles is driven by

// weak references they will be cleared at some point in the future when the reference cleaning logic is run.

void MetadataHandleBlock::do_unloading() {

  for (MetadataHandleBlock* current = this; current != NULL; current = current->_next) {

    for (int index = 0; index < current->_top; index++) {

      HandleRecord* handle = &(current->_handles)[index];

      Metadata* value = handle->value();

      // traverse heap pointers only, not deleted handles or free list

      // pointers

      if (value != NULL && ((intptr_t) value & ptr_tag) == 0) {

        Klass* klass = NULL;

        if (value->is_klass()) {

          klass = (Klass*)value;

        } else if (value->is_method()) {

          Method* m = (Method*)value;

          klass = m->method_holder();

        } else if (value->is_constantPool()) {

          ConstantPool* cp = (ConstantPool*)value;

          klass = cp->pool_holder();

        } else {

          ShouldNotReachHere();

        }

        if (klass->class_loader_data()->is_unloading()) {

          // This needs to be marked so that it's no longer scanned

          // but can't be put on the free list yet. The

          // HandleCleaner will set this to NULL and

          // put it on the free list.

          jlong old_value = Atomic::cmpxchg((jlong*)handle, (jlong) value, (jlong) (ptr_tag));

          if (old_value == (jlong) value) {

            // Success

          } else {

            guarantee(old_value == 0, "only other possible value");

          }

        }

      }

    }

    // the next handle block is valid only if current block is full

    if (current->_top < block_size_in_handles) {

      break;

    }

  }

}