com.fasterxml.jackson.core.sym

## Class ByteQuadsCanonicalizer

- java.lang.Object
- - com.fasterxml.jackson.core.sym.ByteQuadsCanonicalizer

-     public final class ByteQuadsCanonicalizer
      extends Object

  Replacement for `BytesToNameCanonicalizer` which aims at more localized memory access due to flattening of name quad data. Performance improvement modest for simple JSON document data binding (maybe 3%), but should help more for larger symbol tables, or for binary formats like Smile.

  Hash area is divided into 4 sections:

  1. Primary area (1/2 of total size), direct match from hash (LSB)
  2. Secondary area (1/4 of total size), match from `hash (LSB) >> 1`
  3. Tertiary area (1/8 of total size), match from `hash (LSB) >> 2`
  4. Spill-over area (remaining 1/8) with linear scan, insertion order
  and within every area, entries are 4 `int`s, where 1 - 3 ints contain 1 - 12 UTF-8 encoded bytes of name (null-padded), and last int is offset in `_names` that contains actual name Strings.
  Since:
    2.6

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected int` | `_count` Total number of Strings in the symbol table; only used for child tables.
    `protected boolean` | `_failOnDoS` Flag that indicates whether we should throw an exception if enough hash collisions are detected (true); or just worked around (false).
    `protected int[]` | `_hashArea` Primary hash information area: consists of `2 * _hashSize` entries of 16 bytes (4 ints), arranged in a cascading lookup structure (details of which may be tweaked depending on expected rates of collisions).
    `protected boolean` | `_hashShared` Flag that indicates whether underlying data structures for the main hash area are shared or not.
    `protected int` | `_hashSize` Number of slots for primary entries within `_hashArea`; which is at most `1/8` of actual size of the underlying array (4-int slots, primary covers only half of the area; plus, additional area for longer symbols after hash area).
    `protected boolean` | `_intern` Whether canonical symbol Strings are to be intern()ed before added to the table or not.
    `protected int` | `_longNameOffset` Offset within `_hashArea` that follows main slots and contains quads for longer names (13 bytes or longer), and points to the first available int that may be used for appending quads of the next long name.
    `protected String[]` | `_names` Array that contains `String` instances matching entries in `_hashArea`.
    `protected ByteQuadsCanonicalizer` | `_parent` Reference to the root symbol table, for child tables, so that they can merge table information back as necessary.
    `protected int` | `_secondaryStart` Offset within `_hashArea` where secondary entries start
    `protected 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.
    `protected int` | `_spilloverEnd` Pointer to the offset within spill-over area where there is room for more spilled over entries (if any).
    `protected AtomicReference<com.fasterxml.jackson.core.sym.ByteQuadsCanonicalizer.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.
    `protected int` | `_tertiaryShift` Constant that determines size of buckets for tertiary entries: `1 << _tertiaryShift` is the size, and shift value is also used for translating from primary offset into tertiary bucket (shift right by `4 + _tertiaryShift`).
    `protected int` | `_tertiaryStart` Offset within `_hashArea` where tertiary entries start

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected void` | `_reportTooManyCollisions()`
    `String` | `addName(String name, int q1)`
    `String` | `addName(String name, int[] q, int qlen)`
    `String` | `addName(String name, int q1, int q2)`
    `String` | `addName(String name, int q1, int q2, int q3)`
    `int` | `bucketCount()`
    `int` | `calcHash(int q1)`
    `int` | `calcHash(int[] q, int qlen)`
    `int` | `calcHash(int q1, int q2)`
    `int` | `calcHash(int q1, int q2, int q3)`
    `static ByteQuadsCanonicalizer` | `createRoot()` Factory method to call to create a symbol table instance with a randomized seed value.
    `protected static ByteQuadsCanonicalizer` | `createRoot(int seed)`
    `String` | `findName(int q1)`
    `String` | `findName(int[] q, int qlen)`
    `String` | `findName(int q1, int q2)`
    `String` | `findName(int q1, int q2, int q3)`
    `int` | `hashSeed()`
    `ByteQuadsCanonicalizer` | `makeChild(int flags)` Factory method used to create actual symbol table instance to use for parsing.
    `boolean` | `maybeDirty()` Method called to check to quickly see if a child symbol table may have gotten additional entries.
    `int` | `primaryCount()` Method mostly needed by unit tests; calculates number of entries that are in the primary slot set.
    `void` | `release()` Method called by the using code to indicate it is done with this instance.
    `int` | `secondaryCount()` Method mostly needed by unit tests; calculates number of entries in secondary buckets
    `int` | `size()`
    `int` | `spilloverCount()` Method mostly needed by unit tests; calculates number of entries in shared spill-over area
    `int` | `tertiaryCount()` Method mostly needed by unit tests; calculates number of entries in tertiary buckets
    `String` | `toString()`
    `int` | `totalCount()`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Field Detail

    - #### _parent

          protected final ByteQuadsCanonicalizer _parent

      Reference to the root symbol table, for child tables, so that they can merge table information back as necessary.

    - #### _tableInfo

          protected final AtomicReference<com.fasterxml.jackson.core.sym.ByteQuadsCanonicalizer.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.

    - #### _intern

          protected boolean _intern

      Whether canonical symbol Strings are to be intern()ed before added to the table or not.

      NOTE: non-final to allow disabling intern()ing in case of excessive collisions.

    - #### _failOnDoS

          protected final boolean _failOnDoS

      Flag that indicates whether we should throw an exception if enough hash collisions are detected (true); or just worked around (false).
      Since:
        2.4

    - #### _hashArea

          protected int[] _hashArea

      Primary hash information area: consists of `2 * _hashSize` entries of 16 bytes (4 ints), arranged in a cascading lookup structure (details of which may be tweaked depending on expected rates of collisions).

    - #### _hashSize

          protected int _hashSize

      Number of slots for primary entries within `_hashArea`; which is at most `1/8` of actual size of the underlying array (4-int slots, primary covers only half of the area; plus, additional area for longer symbols after hash area).

    - #### _secondaryStart

          protected int _secondaryStart

      Offset within `_hashArea` where secondary entries start

    - #### _tertiaryStart

          protected int _tertiaryStart

      Offset within `_hashArea` where tertiary entries start

    - #### _tertiaryShift

          protected int _tertiaryShift

      Constant that determines size of buckets for tertiary entries: `1 << _tertiaryShift` is the size, and shift value is also used for translating from primary offset into tertiary bucket (shift right by `4 + _tertiaryShift`).

      Default value is 2, for buckets of 4 slots; grows bigger with bigger table sizes.

    - #### _count

          protected int _count

      Total number of Strings in the symbol table; only used for child tables.

    - #### _names

          protected String[] _names

      Array that contains `String` instances matching entries in `_hashArea`. Contains nulls for unused entries. Note that this size is twice that of `_hashArea`

    - #### _spilloverEnd

          protected int _spilloverEnd

      Pointer to the offset within spill-over area where there is room for more spilled over entries (if any). Spill over area is within fixed-size portion of `_hashArea`.

    - #### _longNameOffset

          protected int _longNameOffset

      Offset within `_hashArea` that follows main slots and contains quads for longer names (13 bytes or longer), and points to the first available int that may be used for appending quads of the next long name. Note that long name area follows immediately after the fixed-size main hash area (`_hashArea`).

    - #### _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)

  - ### Method Detail

    - #### createRoot

          public static ByteQuadsCanonicalizer createRoot()

      Factory method to call to create a symbol table instance with a randomized seed value.
      Returns:
        Root instance to use for constructing new child instances

    - #### createRoot

          protected static ByteQuadsCanonicalizer createRoot(int seed)

    - #### makeChild

          public ByteQuadsCanonicalizer makeChild(int flags)

      Factory method used to create actual symbol table instance to use for parsing.
      Parameters:
        `flags` - Bit flags of active `JsonFactory.Feature`s 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()

      Returns:
        number of primary slots table has currently

    - #### maybeDirty

          public boolean maybeDirty()

      Method called to check to quickly see if a child symbol table may have gotten additional entries. Used for checking to see if a child table should be merged into shared table.
      Returns:
        Whether main hash area has been modified

    - #### hashSeed

          public int hashSeed()

    - #### primaryCount

          public int primaryCount()

      Method mostly needed by unit tests; calculates number of entries that are in the primary slot set. These are "perfect" entries, accessible with a single lookup
      Returns:
        Number of entries in the primary hash area

    - #### secondaryCount

          public int secondaryCount()

      Method mostly needed by unit tests; calculates number of entries in secondary buckets
      Returns:
        Number of entries in the secondary hash area

    - #### tertiaryCount

          public int tertiaryCount()

      Method mostly needed by unit tests; calculates number of entries in tertiary buckets
      Returns:
        Number of entries in the tertiary hash area

    - #### spilloverCount

          public int spilloverCount()

      Method mostly needed by unit tests; calculates number of entries in shared spill-over area
      Returns:
        Number of entries in the linear spill-over areay

    - #### totalCount

          public int totalCount()

    - #### toString

          public String toString()

      Overrides:
        `toString` in class `Object`

    - #### findName

          public String findName(int q1)

    - #### findName

          public String findName(int q1,
                                 int q2)

    - #### findName

          public String findName(int q1,
                                 int q2,
                                 int q3)

    - #### findName

          public String findName(int[] q,
                                 int qlen)

    - #### addName

          public String addName(String name,
                                int q1)

    - #### addName

          public String addName(String name,
                                int q1,
                                int q2)

    - #### addName

          public String addName(String name,
                                int q1,
                                int q2,
                                int q3)

    - #### addName

          public String addName(String name,
                                int[] q,
                                int qlen)

    - #### calcHash

          public int calcHash(int q1)

    - #### calcHash

          public int calcHash(int q1,
                              int q2)

    - #### calcHash

          public int calcHash(int q1,
                              int q2,
                              int q3)

    - #### calcHash

          public int calcHash(int[] q,
                              int qlen)

    - #### _reportTooManyCollisions

          protected void _reportTooManyCollisions()

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