com.fasterxml.jackson.core.sym
Class BytesToNameCanonicalizer

java.lang.Object
  extended by com.fasterxml.jackson.core.sym.BytesToNameCanonicalizer

public final class BytesToNameCanonicalizer
extends Object

A caching symbol table implementation used for canonicalizing JSON field names (as Names which are constructed directly from a byte-based input source). Complications arise from trying to do efficient reuse and merging of symbol tables, to be able to make use of usually shared vocabulary of subsequent parsing runs.

Author:
Tatu Saloranta

Field Summary
protected  int _collCount
          Total number of Names in collision buckets (included in _count along with primary entries)
protected  int _collEnd
          Index of the first unused collision bucket entry (== size of the used portion of collision list): less than or equal to 0xFF (255), since max number of entries is 255 (8-bit, minus 0 used as 'empty' marker)
protected  com.fasterxml.jackson.core.sym.BytesToNameCanonicalizer.Bucket[] _collList
          Array of heads of collision bucket chains; size dynamically
protected  int _count
          Total number of Names in the symbol table; only used for child tables.
protected  boolean _intern
          Whether canonical symbol Strings are to be intern()ed before added to the table or not
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.
protected  int[] _mainHash
          Array of 2^N size, which contains combination of 24-bits of hash (0 to indicate 'empty' slot), and 8-bit collision bucket index (0 to indicate empty collision bucket chain; otherwise subtract one from index)
protected  int _mainHashMask
          Mask used to truncate 32-bit hash value to current hash array size; essentially, hash array size - 1 (since hash array sizes are 2^N).
protected  Name[] _mainNames
          Array that contains Name instances matching entries in _mainHash.
protected  BytesToNameCanonicalizer _parent
          Reference to the root symbol table, for child tables, so that they can merge table information back as necessary.
protected  AtomicReference<com.fasterxml.jackson.core.sym.BytesToNameCanonicalizer.TableInfo> _tableInfo
          Member that is only used by the root table instance: root passes immutable state into child instances, and children may return new state if they add entries to the table.
protected static int DEFAULT_TABLE_SIZE
           
protected static int MAX_TABLE_SIZE
          Let's not expand symbol tables past some maximum size; this should protected against OOMEs caused by large documents with unique (~= random) names.
 
Method Summary
 Name addName(String symbolStr, int[] quads, int qlen)
           
 Name addName(String symbolStr, int q1, int q2)
           
 int bucketCount()
           
 int calcHash(int firstQuad)
           
 int calcHash(int[] quads, int qlen)
           
 int calcHash(int firstQuad, int secondQuad)
           
protected static int[] calcQuads(byte[] wordBytes)
           
 int collisionCount()
          Method mostly needed by unit tests; calculates number of entries that are in collision list.
static BytesToNameCanonicalizer createRoot()
          Factory method to call to create a symbol table instance with a randomized seed value.
protected static BytesToNameCanonicalizer createRoot(int hashSeed)
          Factory method that should only be called from unit tests, where seed value should remain the same.
 Name findName(int firstQuad)
          Finds and returns name matching the specified symbol, if such name already exists in the table.
 Name findName(int[] quads, int qlen)
          Finds and returns name matching the specified symbol, if such name already exists in the table; or if not, creates name object, adds to the table, and returns it.
 Name findName(int firstQuad, int secondQuad)
          Finds and returns name matching the specified symbol, if such name already exists in the table.
static Name getEmptyName()
           
 int hashSeed()
           
 BytesToNameCanonicalizer makeChild(boolean canonicalize, boolean intern)
          Factory method used to create actual symbol table instance to use for parsing.
 int maxCollisionLength()
          Method mostly needed by unit tests; calculates length of the longest collision chain.
 boolean maybeDirty()
          Method called to check to quickly see if a child symbol table may have gotten additional entries.
 void release()
          Method called by the using code to indicate it is done with this instance.
protected  void reportTooManyCollisions(int maxLen)
           
 int size()
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

DEFAULT_TABLE_SIZE

protected static final int DEFAULT_TABLE_SIZE
See Also:
Constant Field Values

MAX_TABLE_SIZE

protected static final int MAX_TABLE_SIZE
Let's not expand symbol tables past some maximum size; this should protected against OOMEs caused by large documents with unique (~= random) names.

See Also:
Constant Field Values

_parent

protected final BytesToNameCanonicalizer _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.BytesToNameCanonicalizer.TableInfo> _tableInfo
Member that is only used by the root table instance: root passes immutable state into child instances, and children may return new state if they add entries to the table. Child tables do NOT use the reference.


_intern

protected final boolean _intern
Whether canonical symbol Strings are to be intern()ed before added to the table or not


_count

protected int _count
Total number of Names in the symbol table; only used for child tables.


_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

_mainHashMask

protected int _mainHashMask
Mask used to truncate 32-bit hash value to current hash array size; essentially, hash array size - 1 (since hash array sizes are 2^N).


_mainHash

protected int[] _mainHash
Array of 2^N size, which contains combination of 24-bits of hash (0 to indicate 'empty' slot), and 8-bit collision bucket index (0 to indicate empty collision bucket chain; otherwise subtract one from index)


_mainNames

protected Name[] _mainNames
Array that contains Name instances matching entries in _mainHash. Contains nulls for unused entries.


_collList

protected com.fasterxml.jackson.core.sym.BytesToNameCanonicalizer.Bucket[] _collList
Array of heads of collision bucket chains; size dynamically


_collCount

protected int _collCount
Total number of Names in collision buckets (included in _count along with primary entries)


_collEnd

protected int _collEnd
Index of the first unused collision bucket entry (== size of the used portion of collision list): less than or equal to 0xFF (255), since max number of entries is 255 (8-bit, minus 0 used as 'empty' marker)

Method Detail

createRoot

public static BytesToNameCanonicalizer createRoot()
Factory method to call to create a symbol table instance with a randomized seed value.


createRoot

protected static BytesToNameCanonicalizer createRoot(int hashSeed)
Factory method that should only be called from unit tests, where seed value should remain the same.


makeChild

public BytesToNameCanonicalizer makeChild(boolean canonicalize,
                                          boolean intern)
Factory method used to create actual symbol table instance to use for parsing.

Parameters:
intern - Whether canonical symbol Strings should be interned or not

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()

bucketCount

public int bucketCount()
Since:
2.1

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.


hashSeed

public int hashSeed()
Since:
2.1

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.

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

Since:
2.1

getEmptyName

public static Name getEmptyName()

findName

public Name findName(int firstQuad)
Finds and returns name matching the specified symbol, if such name already exists in the table. If not, will return null.

Note: separate methods to optimize common case of short element/attribute names (4 or less ascii characters)

Parameters:
firstQuad - int32 containing first 4 bytes of the name; if the whole name less than 4 bytes, padded with zero bytes in front (zero MSBs, ie. right aligned)
Returns:
Name matching the symbol passed (or constructed for it)

findName

public Name findName(int firstQuad,
                     int secondQuad)
Finds and returns name matching the specified symbol, if such name already exists in the table. If not, will return null.

Note: separate methods to optimize common case of relatively short element/attribute names (8 or less ascii characters)

Parameters:
firstQuad - int32 containing first 4 bytes of the name.
secondQuad - int32 containing bytes 5 through 8 of the name; if less than 8 bytes, padded with up to 3 zero bytes in front (zero MSBs, ie. right aligned)
Returns:
Name matching the symbol passed (or constructed for it)

findName

public Name findName(int[] quads,
                     int qlen)
Finds and returns name matching the specified symbol, if such name already exists in the table; or if not, creates name object, adds to the table, and returns it.

Note: this is the general purpose method that can be called for names of any length. However, if name is less than 9 bytes long, it is preferable to call the version optimized for short names.

Parameters:
quads - Array of int32s, each of which contain 4 bytes of encoded name
qlen - Number of int32s, starting from index 0, in quads parameter
Returns:
Name matching the symbol passed (or constructed for it)

addName

public Name addName(String symbolStr,
                    int q1,
                    int q2)

addName

public Name addName(String symbolStr,
                    int[] quads,
                    int qlen)

calcHash

public int calcHash(int firstQuad)

calcHash

public int calcHash(int firstQuad,
                    int secondQuad)

calcHash

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

calcQuads

protected static int[] calcQuads(byte[] wordBytes)

reportTooManyCollisions

protected void reportTooManyCollisions(int maxLen)
Since:
2.1


Copyright © 2012 FasterXML. All Rights Reserved.