blockiterator.java

嵌入式数据库Berkeley DB-4.5.20源代码

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 2000-2006
 *      Oracle Corporation.  All rights reserved.
 *
 * $Id: BlockIterator.java,v 12.3 2006/09/08 20:32:13 bostic Exp $
 */

package com.sleepycat.collections;

import java.util.ListIterator;
import java.util.NoSuchElementException;

import com.sleepycat.compat.DbCompat;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.OperationStatus;
import com.sleepycat.util.keyrange.KeyRange;

/**
 * An iterator that does need closing because a cursor is not kept open across
 * method calls.  A cursor is opened to read a block of records at a time and
 * then closed before the method returns.
 *
 * @author Mark Hayes
 */
class BlockIterator implements BaseIterator {

    private StoredCollection coll;
    private boolean writeAllowed;

    /**
     * Slots for a block of record keys and values.  The priKeys array is only
     * used for secondary databases; otherwise it is set to the keys array.
     */
    private byte[][] keys;
    private byte[][] priKeys;
    private byte[][] values;

    /**
     * The slot index of the record that would be returned by next().
     * nextIndex is always greater or equal to zero.  If the next record is not
     * available, then nextIndex is equal to keys.length or keys[nextIndex] is
     * null.
     */
    private int nextIndex;

    /**
     * The slot index of the record last returned by next() or previous(), or
     * the record inserted by add().  dataIndex is -1 if the data record is not
     * available.  If greater or equal to zero, the slot at dataIndex is always
     * non-null.
     */
    private int dataIndex;

    /**
     * The iterator data last returned by next() or previous().  This value is
     * set to null if dataIndex is -1, or if the state of the iterator is such
     * that set() or remove() cannot be called.  For example, after add() this
     * field is set to null, even though the dataIndex is still valid.
     */
    private Object dataObject;

    /**
     * Creates an iterator.
     */
    BlockIterator(StoredCollection coll, boolean writeAllowed, int blockSize) {

        this.coll = coll;
        this.writeAllowed = writeAllowed;

        keys = new byte[blockSize][];
        priKeys = coll.isSecondary() ? (new byte[blockSize][]) : keys;
        values = new byte[blockSize][];

        nextIndex = blockSize;
        dataIndex = -1;
        dataObject = null;
    }

    /**
     * Copy constructor.
     */
    private BlockIterator(BlockIterator o) {

        coll = o.coll;
        writeAllowed = o.writeAllowed;

        keys = copyArray(o.keys);
        priKeys = coll.isSecondary() ? copyArray(o.priKeys) : keys;
        values = copyArray(o.values);

        nextIndex = o.nextIndex;
        dataIndex = o.dataIndex;
        dataObject = o.dataObject;
    }

    /**
     * Copies an array of byte arrays.
     */
    private byte[][] copyArray(byte[][] a) {

        byte[][] b = new byte[a.length][];
        for (int i = 0; i < b.length; i += 1) {
            if (a[i] != null) {
                b[i] = KeyRange.copyBytes(a[i]);
            }
        }
        return b;
    }

    /**
     * Returns whether the element at nextIndex is available.
     */
    private boolean isNextAvailable() {

        return (nextIndex < keys.length) &&
               (keys[nextIndex] != null);
    }

    /**
     * Returns whether the element at nextIndex-1 is available.
     */
    private boolean isPrevAvailable() {

        return (nextIndex > 0) &&
               (keys[nextIndex - 1] != null);
    }

    /**
     * Returns the record number at the given slot position.
     */
    private int getRecordNumber(int i) {

        if (coll.view.btreeRecNumDb) {
            DataCursor cursor = null;
            try {
                cursor = new DataCursor(coll.view, false);
                if (moveCursor(i, cursor)) {
                    return cursor.getCurrentRecordNumber();
                } else {
                    throw new IllegalStateException();
                }
            } catch (DatabaseException e) {
                throw StoredContainer.convertException(e);
            } finally {
                closeCursor(cursor);
            }
        } else {
            DatabaseEntry entry = new DatabaseEntry(keys[i]);
            return DbCompat.getRecordNumber(entry);
        }
    }

    /**
     * Sets dataObject to the iterator data for the element at dataIndex.
     */
    private void makeDataObject() {

        int i = dataIndex;
        DatabaseEntry keyEntry = new DatabaseEntry(keys[i]);
        DatabaseEntry priKeyEntry = (keys != priKeys)
                                    ? (new DatabaseEntry(priKeys[i]))
                                    : keyEntry;
        DatabaseEntry valuesEntry = new DatabaseEntry(values[i]);

        dataObject = coll.makeIteratorData(this, keyEntry, priKeyEntry,
                                           valuesEntry);
    }

    /**
     * Sets all slots to null.
     */
    private void clearSlots() {

        for (int i = 0; i < keys.length; i += 1) {
            keys[i] = null;
            priKeys[i] = null;
            values[i] = null;
        }
    }

    /**
     * Sets a given slot using the data in the given cursor.
     */
    private void setSlot(int i, DataCursor cursor) {

        keys[i] = KeyRange.getByteArray(cursor.getKeyThang());

        if (keys != priKeys) {
            priKeys[i] = KeyRange.getByteArray
                (cursor.getPrimaryKeyThang());
        }

        values[i] = KeyRange.getByteArray(cursor.getValueThang());
    }

    /**
     * Inserts an added record at a given slot position and shifts other slots
     * accordingly.  Also adjusts nextIndex and sets dataIndex to -1.
     */
    private void insertSlot(int i, DataCursor cursor) {

        if (i < keys.length) {
            for (int j = keys.length - 1; j > i; j -= 1) {

                /* Shift right. */
                keys[j] = keys[j - 1];
                priKeys[j] = priKeys[j - 1];
                values[j] = values[j - 1];

                /* Bump key in recno-renumber database. */
                if (coll.view.recNumRenumber && keys[j] != null) {
                    bumpRecordNumber(j);
                }
            }
            nextIndex += 1;
        } else {
            if (i != keys.length) {
                throw new IllegalStateException();
            }
            i -= 1;
            for (int j = 0; j < i; j += 1) {
                /* Shift left. */
                keys[j] = keys[j + 1];
                priKeys[j] = priKeys[j + 1];
                values[j] = values[j + 1];
            }
        }
        setSlot(i, cursor);
        dataIndex = -1;
    }

    /**
     * Increments the record number key at the given slot.
     */
    private void bumpRecordNumber(int i) {

        DatabaseEntry entry = new DatabaseEntry(keys[i]);
        DbCompat.setRecordNumber(entry,
                                 DbCompat.getRecordNumber(entry) + 1);
        keys[i] = entry.getData();
    }

    /**
     * Deletes the given slot, adjusts nextIndex and sets dataIndex to -1.
     */
    private void deleteSlot(int i) {

        for (int j = i + 1; j < keys.length; j += 1) {
            keys[j - 1] = keys[j];
            priKeys[j - 1] = priKeys[j];
            values[j - 1] = values[j];
        }
        int last = keys.length - 1;
        keys[last] = null;
        priKeys[last] = null;
        values[last] = null;

        if (nextIndex > i) {
            nextIndex -= 1;
        }
        dataIndex = -1;
    }

    /**
     * Moves the cursor to the key/data at the given slot, and returns false
     * if the reposition (search) fails.
     */
    private boolean moveCursor(int i, DataCursor cursor)
        throws DatabaseException {

        return cursor.repositionExact(keys[i], priKeys[i], values[i], false);
    }

    /**
     * Closes the given cursor if non-null.
     */
    private void closeCursor(DataCursor cursor) {

        if (cursor != null) {
            try {
                cursor.close();
            } catch (DatabaseException e) {
                throw StoredContainer.convertException(e);
            }
        }
    }

    // --- begin Iterator/ListIterator methods ---

    public boolean hasNext() {

        if (isNextAvailable()) {
            return true;
        }
        DataCursor cursor = null;
        try {
            cursor = new DataCursor(coll.view, writeAllowed);
            int prev = nextIndex - 1;
            boolean found = false;

            if (keys[prev] == null) {
                /* Get the first record for an uninitialized iterator. */
                OperationStatus status = cursor.getFirst(false);
                if (status == OperationStatus.SUCCESS) {
                    found = true;
                    nextIndex = 0;
                }
            } else {
                /* Reposition to the last known key/data pair. */
                int repos = cursor.repositionRange
                    (keys[prev], priKeys[prev], values[prev], false);

                if (repos == DataCursor.REPOS_EXACT) {

                    /*
                     * The last known key/data pair was found and will now be
                     * in slot zero.
                     */
                    found = true;
                    nextIndex = 1;

                    /* The data object is now in slot zero or not available. */
                    if (dataIndex == prev) {
                        dataIndex = 0;
                    } else {
                        dataIndex = -1;
                        dataObject = null;
                    }
                } else if (repos == DataCursor.REPOS_NEXT) {

                    /*
                     * The last known key/data pair was not found, but the
                     * following record was found and it will be in slot zero.
                     */
                    found = true;
                    nextIndex = 0;

                    /* The data object is no longer available. */
                    dataIndex = -1;
                    dataObject = null;
                } else {
                    if (repos != DataCursor.REPOS_EOF) {
                        throw new IllegalStateException();
                    }
                }
            }

            if (found) {
                /* Clear all slots first in case an exception occurs below. */
                clearSlots();

                /* Attempt to fill all slots with records. */
                int i = 0;
                boolean done = false;
                while (!done) {
                    setSlot(i, cursor);
                    i += 1;
                    if (i < keys.length) {
                        OperationStatus status = coll.iterateDuplicates() ?
                                                 cursor.getNext(false) :
                                                 cursor.getNextNoDup(false);
                        if (status != OperationStatus.SUCCESS) {