Field Detail

• HASH_MULT

  public static final int HASH_MULT

  See Also:

  Constant Field Values

• _parent

  protected final CharsToNameCanonicalizer _parent

  Sharing of learnt symbols is done by optional linking of symbol table instances with their parents. When parent linkage is defined, and child instance is released (call to release), parent's shared tables may be updated from the child instance.

• _tableInfo

  protected final AtomicReference<com.fasterxml.jackson.core.sym.CharsToNameCanonicalizer.TableInfo> _tableInfo

  Member that is only used by the root table instance: root passes immutable state info child instances, and children may return new state if they add entries to the table. Child tables do NOT use the reference.

• _seed

  protected final int _seed

  Seed value we use as the base to make hash codes non-static between different runs, but still stable for lifetime of a single symbol table instance. This is done for security reasons, to avoid potential DoS attack via hash collisions.

  Since:

  2.1

• _flags

  protected final int _flags

• _canonicalize

  protected boolean _canonicalize

  Whether any canonicalization should be attempted (whether using intern or not.

  NOTE: non-final since we may need to disable this with overflow.

• _symbols

  protected String[] _symbols

  Primary matching symbols; it's expected most match occur from here.

• _buckets

  protected com.fasterxml.jackson.core.sym.CharsToNameCanonicalizer.Bucket[] _buckets

  Overflow buckets; if primary doesn't match, lookup is done from here.

  Note: Number of buckets is half of number of symbol entries, on assumption there's less need for buckets.

• _size

  protected int _size

  Current size (number of entries); needed to know if and when rehash.

• _sizeThreshold

  protected int _sizeThreshold

  Limit that indicates maximum size this instance can hold before it needs to be expanded and rehashed. Calculated using fill factor passed in to constructor.

• _indexMask

  protected int _indexMask

  Mask used to get index from hash values; equal to _buckets.length - 1, when _buckets.length is a power of two.

• _longestCollisionList

  protected int _longestCollisionList

  We need to keep track of the longest collision list; this is needed both to indicate problems with attacks and to allow flushing for other cases.

  Since:

  2.1

• _hashShared

  protected boolean _hashShared

  Flag that indicates whether underlying data structures for the main hash area are shared or not. If they are, then they need to be handled in copy-on-write way, i.e. if they need to be modified, a copy needs to be made first; at this point it will not be shared any more, and can be modified.

  This flag needs to be checked both when adding new main entries, and when adding new collision list queues (i.e. creating a new collision list head entry)

• _overflows

  protected BitSet _overflows

  Lazily constructed structure that is used to keep track of collision buckets that have overflowed once: this is used to detect likely attempts at denial-of-service attacks that uses hash collisions.

  Since:

  2.4

Method Detail

• createRoot

  public static CharsToNameCanonicalizer createRoot()

  Method called to create root canonicalizer for a JsonFactory instance. Root instance is never used directly; its main use is for storing and sharing underlying symbol arrays as needed.

  Returns:

  Root instance to use for constructing new child instances

• createRoot

  protected static CharsToNameCanonicalizer createRoot(int seed)

• makeChild

  public CharsToNameCanonicalizer makeChild(int flags)

  "Factory" method; will create a new child instance of this symbol table. It will be a copy-on-write instance, ie. it will only use read-only copy of parent's data, but when changes are needed, a copy will be created.

  Note: while this method is synchronized, it is generally not safe to both use makeChild/mergeChild, AND to use instance actively. Instead, a separate 'root' instance should be used on which only makeChild/mergeChild are called, but instance itself is not used as a symbol table.

  Parameters:

  flags - Bit flags of active JsonFactory.Features enabled.

  Returns:

  Actual canonicalizer instance that can be used by a parser

• release

  public void release()

  Method called by the using code to indicate it is done with this instance. This lets instance merge accumulated changes into parent (if need be), safely and efficiently, and without calling code having to know about parent information.

• size

  public int size()

  Returns:

  Number of symbol entries contained by this canonicalizer instance

• bucketCount

  public int bucketCount()

  Method for checking number of primary hash buckets this symbol table uses.

  Returns:

  number of primary slots table has currently

• maybeDirty

  public boolean maybeDirty()

• hashSeed

  public int hashSeed()

• collisionCount

  public int collisionCount()

  Method mostly needed by unit tests; calculates number of entries that are in collision list. Value can be at most (size() - 1), but should usually be much lower, ideally 0.

  Returns:

  Number of collisions in the primary hash area

  Since:

  2.1

• maxCollisionLength

  public int maxCollisionLength()

  Method mostly needed by unit tests; calculates length of the longest collision chain. This should typically be a low number, but may be up to size() - 1 in the pathological case

  Returns:

  Length of the collision chain

  Since:

  2.1

• findSymbol

  public String findSymbol(char[] buffer,
                           int start,
                           int len,
                           int h)
                    throws IOException

  Throws:

  IOException

• _hashToIndex

  public int _hashToIndex(int rawHash)

  Helper method that takes in a "raw" hash value, shuffles it as necessary, and truncates to be used as the index.

  Parameters:

  rawHash - Raw hash value to use for calculating index

  Returns:

  Index value calculated

• calcHash

  public int calcHash(char[] buffer,
                      int start,
                      int len)

  Implementation of a hashing method for variable length Strings. Most of the time intention is that this calculation is done by caller during parsing, not here; however, sometimes it needs to be done for parsed "String" too.

  Parameters:

  buffer - Input buffer that contains name to decode

  start - Pointer to the first character of the name

  len - Length of String; has to be at least 1 (caller guarantees)

  Returns:

  Hash code calculated

• calcHash

  public int calcHash(String key)

• _reportTooManyCollisions

  protected void _reportTooManyCollisions(int maxLen)
                                   throws StreamConstraintsException

  Parameters:

  maxLen - Maximum allowed length of collision chain

  Throws:

  StreamConstraintsException - if there are too many collisions (was an IllegalStateException before v2.15)

  Since:

  2.1

• verifyInternalConsistency

  protected void verifyInternalConsistency()

  Diagnostics method that will verify that internal data structures are consistent; not meant as user-facing method but only for test suites and possible troubleshooting.

  Since:

  2.10