com.fasterxml.jackson.core.sym.BytesToNameCanonicalizer Maven / Gradle / Ivy
Show all versions of ehcache Show documentation
package com.fasterxml.jackson.core.sym;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicReference;
import com.fasterxml.jackson.core.util.ArraysCompat;
import com.fasterxml.jackson.core.util.InternCache;
/**
* A caching symbol table implementation used for canonicalizing JSON field
* names (as {@link Name}s 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
*/
public final class BytesToNameCanonicalizer
{
protected static final int DEFAULT_TABLE_SIZE = 64;
/**
* Let's not expand symbol tables past some maximum size;
* this should protected against OOMEs caused by large documents
* with unique (~= random) names.
*/
protected static final int MAX_TABLE_SIZE = 0x10000; // 64k entries == 256k mem
/**
* Let's only share reasonably sized symbol tables. Max size set to 3/4 of 16k;
* this corresponds to 64k main hash index. This should allow for enough distinct
* names for almost any case.
*/
final static int MAX_ENTRIES_FOR_REUSE = 6000;
/**
* Also: to thwart attacks based on hash collisions (which may or may not
* be cheap to calculate), we will need to detect "too long"
* collision chains. Let's start with static value of 255 entries
* for the longest legal chain.
*
* Note: longest chain we have been able to produce without malicious
* intent has been 60 (with "com.fasterxml.jackson.core.main.TestWithTonsaSymbols");
* our setting should be reasonable here.
*
* @since 2.1
*/
final static int MAX_COLL_CHAIN_LENGTH = 255;
/**
* And to support reduce likelihood of accidental collisions causing
* exceptions, let's prevent reuse of tables with long collision
* overflow lists as well.
*
* @since 2.1
*/
final static int MAX_COLL_CHAIN_FOR_REUSE = 63;
/**
* No point in trying to construct tiny tables, just need to resize
* soon.
*/
final static int MIN_HASH_SIZE = 16;
/**
* We will also need to defin
*/
final static int INITIAL_COLLISION_LEN = 32;
/**
* Bucket index is 8 bits, and value 0 is reserved to represent
* 'empty' status.
*/
final static int LAST_VALID_BUCKET = 0xFE;
/*
/**********************************************************
/* Linkage, needed for merging symbol tables
/**********************************************************
*/
/**
* Reference to the root symbol table, for child tables, so
* that they can merge table information back as necessary.
*/
final protected BytesToNameCanonicalizer _parent;
/**
* 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.
*/
final protected AtomicReference _tableInfo;
/**
* 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
*/
final private int _hashSeed;
/*
/**********************************************************
/* Main table state
/**********************************************************
*/
/**
* Whether canonical symbol Strings are to be intern()ed before added
* to the table or not
*/
protected final boolean _intern;
// // // First, global information
/**
* Total number of Names in the symbol table;
* only used for child tables.
*/
protected int _count;
/**
* 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
*/
protected int _longestCollisionList;
// // // Then information regarding primary hash array and its
// // // matching Name array
/**
* 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 int _mainHashMask;
/**
* 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[] _mainHash;
/**
* Array that contains Name instances matching
* entries in _mainHash. Contains nulls for unused
* entries.
*/
protected Name[] _mainNames;
// // // Then the collision/spill-over area info
/**
* Array of heads of collision bucket chains; size dynamically
*/
protected Bucket[] _collList;
/**
* Total number of Names in collision buckets (included in
* _count along with primary entries)
*/
protected int _collCount;
/**
* 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 int _collEnd;
// // // Info regarding pending rehashing...
/**
* This flag is set if, after adding a new entry, it is deemed
* that a rehash is warranted if any more entries are to be added.
*/
private transient boolean _needRehash;
/*
/**********************************************************
/* Sharing, versioning
/**********************************************************
*/
// // // Which of the buffers may be shared (and are copy-on-write)?
/**
* 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)
*/
private boolean _mainHashShared;
private boolean _mainNamesShared;
/**
* Flag that indicates whether underlying data structures for
* the collision list 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 when adding new collision entries.
*/
private boolean _collListShared;
/*
/**********************************************************
/* Life-cycle: constructors
/**********************************************************
*/
/**
* Constructor used for creating per-JsonFactory "root"
* symbol tables: ones used for merging and sharing common symbols
*
* @param hashSize Initial hash area size
* @param intern Whether Strings contained should be {@link String#intern}ed
* @param seed Random seed valued used to make it more difficult to cause
* collisions (used for collision-based DoS attacks).
*/
private BytesToNameCanonicalizer(int hashSize, boolean intern, int seed)
{
_parent = null;
_hashSeed = seed;
_intern = intern;
// Sanity check: let's now allow hash sizes below certain minimum value
if (hashSize < MIN_HASH_SIZE) {
hashSize = MIN_HASH_SIZE;
} else {
/* Also; size must be 2^N; otherwise hash algorithm won't
* work... so let's just pad it up, if so
*/
if ((hashSize & (hashSize - 1)) != 0) { // only true if it's 2^N
int curr = MIN_HASH_SIZE;
while (curr < hashSize) {
curr += curr;
}
hashSize = curr;
}
}
_tableInfo = new AtomicReference(initTableInfo(hashSize));
}
/**
* Constructor used when creating a child instance
*/
private BytesToNameCanonicalizer(BytesToNameCanonicalizer parent, boolean intern, int seed,
TableInfo state)
{
_parent = parent;
_hashSeed = seed;
_intern = intern;
_tableInfo = null; // not used by child tables
// Then copy shared state
_count = state.count;
_mainHashMask = state.mainHashMask;
_mainHash = state.mainHash;
_mainNames = state.mainNames;
_collList = state.collList;
_collCount = state.collCount;
_collEnd = state.collEnd;
_longestCollisionList = state.longestCollisionList;
// and then set other state to reflect sharing status
_needRehash = false;
_mainHashShared = true;
_mainNamesShared = true;
_collListShared = true;
}
/*
public TableInfo(int count, int mainHashMask, int[] mainHash, Name[] mainNames,
Bucket[] collList, int collCount, int collEnd, int longestCollisionList)
*/
private TableInfo initTableInfo(int hashSize)
{
return new TableInfo(0, // count
hashSize - 1, // mainHashMask
new int[hashSize], // mainHash
new Name[hashSize], // mainNames
null, // collList
0, // collCount,
0, // collEnd
0 // longestCollisionList
);
}
/*
/**********************************************************
/* Life-cycle: factory methods, merging
/**********************************************************
*/
/**
* Factory method to call to create a symbol table instance with a
* randomized seed value.
*/
public static BytesToNameCanonicalizer createRoot()
{
/* [Issue-21]: Need to use a variable seed, to thwart hash-collision
* based attacks.
*/
long now = System.currentTimeMillis();
// ensure it's not 0; and might as well require to be odd so:
int seed = (((int) now) + ((int) (now >>> 32))) | 1;
return createRoot(seed);
}
/**
* Factory method that should only be called from unit tests, where seed
* value should remain the same.
*/
protected static BytesToNameCanonicalizer createRoot(int hashSeed) {
return new BytesToNameCanonicalizer(DEFAULT_TABLE_SIZE, true, hashSeed);
}
/**
* Factory method used to create actual symbol table instance to
* use for parsing.
*
* @param intern Whether canonical symbol Strings should be interned
* or not
*/
public BytesToNameCanonicalizer makeChild(boolean canonicalize,
boolean intern)
{
return new BytesToNameCanonicalizer(this, intern, _hashSeed, _tableInfo.get());
}
/**
* 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
*/
public void release()
{
// we will try to merge if child table has new entries
if (_parent != null && maybeDirty()) {
_parent.mergeChild(new TableInfo(this));
/* Let's also mark this instance as dirty, so that just in
* case release was too early, there's no corruption of possibly shared data.
*/
_mainHashShared = true;
_mainNamesShared = true;
_collListShared = true;
}
}
private void mergeChild(TableInfo childState)
{
final int childCount = childState.count;
TableInfo currState = _tableInfo.get();
// Only makes sense if child actually has more entries
if (childCount <= currState.count) {
return;
}
/* One caveat: let's try to avoid problems with
* degenerate cases of documents with generated "random"
* names: for these, symbol tables would bloat indefinitely.
* One way to do this is to just purge tables if they grow
* too large, and that's what we'll do here.
*/
if (childCount > MAX_ENTRIES_FOR_REUSE
|| childState.longestCollisionList > MAX_COLL_CHAIN_FOR_REUSE) {
/* Should there be a way to get notified about this
* event, to log it or such? (as it's somewhat abnormal
* thing to happen)
*/
// At any rate, need to clean up the tables
childState = initTableInfo(DEFAULT_TABLE_SIZE);
}
_tableInfo.compareAndSet(currState, childState);
}
/*
/**********************************************************
/* API, accessors
/**********************************************************
*/
public int size()
{
if (_tableInfo != null) { // root table
return _tableInfo.get().count;
}
// nope, child table
return _count;
}
/**
* @since 2.1
*/
public int bucketCount() { return _mainHash.length; }
/**
* 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.
*/
public boolean maybeDirty() {
return !_mainHashShared;
}
/**
* @since 2.1
*/
public int hashSeed() { return _hashSeed; }
/**
* Method mostly needed by unit tests; calculates number of
* entries that are in collision list. Value can be at most
* ({@link #size} - 1), but should usually be much lower, ideally 0.
*
* @since 2.1
*/
public int collisionCount() {
return _collCount;
}
/**
* 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 {@link #size} - 1 in the pathological case
*
* @since 2.1
*/
public int maxCollisionLength() {
return _longestCollisionList;
}
/*
/**********************************************************
/* Public API, accessing symbols:
/**********************************************************
*/
public static Name getEmptyName()
{
return Name1.getEmptyName();
}
/**
* 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)
*
* @param 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)
*
* @return Name matching the symbol passed (or constructed for
* it)
*/
public Name findName(int firstQuad)
{
int hash = calcHash(firstQuad);
int ix = (hash & _mainHashMask);
int val = _mainHash[ix];
/* High 24 bits of the value are low 24 bits of hash (low 8 bits
* are bucket index)... match?
*/
if ((((val >> 8) ^ hash) << 8) == 0) { // match
// Ok, but do we have an actual match?
Name name = _mainNames[ix];
if (name == null) { // main slot empty; can't find
return null;
}
if (name.equals(firstQuad)) {
return name;
}
} else if (val == 0) { // empty slot? no match
return null;
}
// Maybe a spill-over?
val &= 0xFF;
if (val > 0) { // 0 means 'empty'
val -= 1; // to convert from 1-based to 0...
Bucket bucket = _collList[val];
if (bucket != null) {
return bucket.find(hash, firstQuad, 0);
}
}
// Nope, no match whatsoever
return null;
}
/**
* 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)
*
* @param firstQuad int32 containing first 4 bytes of the name.
* @param 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)
*
* @return Name matching the symbol passed (or constructed for it)
*/
public Name findName(int firstQuad, int secondQuad)
{
int hash = (secondQuad == 0) ? calcHash(firstQuad) : calcHash(firstQuad, secondQuad);
int ix = (hash & _mainHashMask);
int val = _mainHash[ix];
/* High 24 bits of the value are low 24 bits of hash (low 8 bits
* are bucket index)... match?
*/
if ((((val >> 8) ^ hash) << 8) == 0) { // match
// Ok, but do we have an actual match?
Name name = _mainNames[ix];
if (name == null) { // main slot empty; can't find
return null;
}
if (name.equals(firstQuad, secondQuad)) {
return name;
}
} else if (val == 0) { // empty slot? no match
return null;
}
// Maybe a spill-over?
val &= 0xFF;
if (val > 0) { // 0 means 'empty'
val -= 1; // to convert from 1-based to 0...
Bucket bucket = _collList[val];
if (bucket != null) {
return bucket.find(hash, firstQuad, secondQuad);
}
}
// Nope, no match whatsoever
return null;
}
/**
* 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.
*
* @param quads Array of int32s, each of which contain 4 bytes of
* encoded name
* @param qlen Number of int32s, starting from index 0, in quads
* parameter
*
* @return Name matching the symbol passed (or constructed for it)
*/
public Name findName(int[] quads, int qlen)
{
if (qlen < 3) { // another sanity check
return findName(quads[0], (qlen < 2) ? 0 : quads[1]);
}
int hash = calcHash(quads, qlen);
// (for rest of comments regarding logic, see method above)
int ix = (hash & _mainHashMask);
int val = _mainHash[ix];
if ((((val >> 8) ^ hash) << 8) == 0) {
Name name = _mainNames[ix];
if (name == null // main slot empty; no collision list then either
|| name.equals(quads, qlen)) { // should be match, let's verify
return name;
}
} else if (val == 0) { // empty slot? no match
return null;
}
val &= 0xFF;
if (val > 0) { // 0 means 'empty'
val -= 1; // to convert from 1-based to 0...
Bucket bucket = _collList[val];
if (bucket != null) {
return bucket.find(hash, quads, qlen);
}
}
return null;
}
/*
/**********************************************************
/* API, mutators
/**********************************************************
*/
public Name addName(String symbolStr, int q1, int q2)
{
if (_intern) {
symbolStr = InternCache.instance.intern(symbolStr);
}
int hash = (q2 == 0) ? calcHash(q1) : calcHash(q1, q2);
Name symbol = constructName(hash, symbolStr, q1, q2);
_addSymbol(hash, symbol);
return symbol;
}
public Name addName(String symbolStr, int[] quads, int qlen)
{
if (_intern) {
symbolStr = InternCache.instance.intern(symbolStr);
}
int hash;
if (qlen < 3) {
hash = (qlen == 1) ? calcHash(quads[0]) : calcHash(quads[0], quads[1]);
} else {
hash = calcHash(quads, qlen);
}
Name symbol = constructName(hash, symbolStr, quads, qlen);
_addSymbol(hash, symbol);
return symbol;
}
/*
/**********************************************************
/* Helper methods
/**********************************************************
*/
/* Note on hash calculation: we try to make it more difficult to
* generate collisions automatically; part of this is to avoid
* simple "multiply-add" algorithm (like JDK String.hashCode()),
* and add bit of shifting. And other part is to make this
* non-linear, at least for shorter symbols.
*/
// JDK uses 31; other fine choices are 33 and 65599, let's use 33
// as it seems to give fewest collisions for us
// (see [http://www.cse.yorku.ca/~oz/hash.html] for details)
private final static int MULT = 33;
private final static int MULT2 = 65599;
private final static int MULT3 = 31;
public int calcHash(int firstQuad)
{
int hash = firstQuad ^ _hashSeed;
hash += (hash >>> 15); // to xor hi- and low- 16-bits
hash ^= (hash >>> 9); // as well as lowest 2 bytes
return hash;
}
public int calcHash(int firstQuad, int secondQuad)
{
/* For two quads, let's change algorithm a bit, to spice
* things up (can do bit more processing anyway)
*/
int hash = firstQuad;
hash ^= (hash >>> 15); // try mixing first and second byte pairs first
hash += (secondQuad * MULT); // then add second quad
hash ^= _hashSeed;
hash += (hash >>> 7); // and shuffle some more
return hash;
}
public int calcHash(int[] quads, int qlen)
{
// Note: may be called for qlen < 3; but has at least one int
if (qlen < 3) {
throw new IllegalArgumentException();
}
/* And then change handling again for "multi-quad" case; mostly
* to make calculation of collisions less fun. For example,
* add seed bit later in the game, and switch plus/xor around,
* use different shift lengths.
*/
int hash = quads[0] ^ _hashSeed;
hash += (hash >>> 9);
hash *= MULT;
hash += quads[1];
hash *= MULT2;
hash += (hash >>> 15);
hash ^= quads[2];
hash += (hash >>> 17);
for (int i = 3; i < qlen; ++i) {
hash = (hash * MULT3) ^ quads[i];
// for longer entries, mess a bit in-between too
hash += (hash >>> 3);
hash ^= (hash << 7);
}
// and finally shuffle some more once done
hash += (hash >>> 15); // to get high-order bits to mix more
hash ^= (hash << 9); // as well as lowest 2 bytes
return hash;
}
// Method only used by unit tests
protected static int[] calcQuads(byte[] wordBytes)
{
int blen = wordBytes.length;
int[] result = new int[(blen + 3) / 4];
for (int i = 0; i < blen; ++i) {
int x = wordBytes[i] & 0xFF;
if (++i < blen) {
x = (x << 8) | (wordBytes[i] & 0xFF);
if (++i < blen) {
x = (x << 8) | (wordBytes[i] & 0xFF);
if (++i < blen) {
x = (x << 8) | (wordBytes[i] & 0xFF);
}
}
}
result[i >> 2] = x;
}
return result;
}
/*
/**********************************************************
/* Standard methods
/**********************************************************
*/
/*
@Override
public String toString()
{
StringBuilder sb = new StringBuilder();
sb.append("[BytesToNameCanonicalizer, size: ");
sb.append(_count);
sb.append('/');
sb.append(_mainHash.length);
sb.append(", ");
sb.append(_collCount);
sb.append(" coll; avg length: ");
// Average length: minimum of 1 for all (1 == primary hit);
// and then 1 per each traversal for collisions/buckets
//int maxDist = 1;
int pathCount = _count;
for (int i = 0; i < _collEnd; ++i) {
int spillLen = _collList[i].length();
for (int j = 1; j <= spillLen; ++j) {
pathCount += j;
}
}
double avgLength;
if (_count == 0) {
avgLength = 0.0;
} else {
avgLength = (double) pathCount / (double) _count;
}
// let's round up a bit (two 2 decimal places)
//avgLength -= (avgLength % 0.01);
sb.append(avgLength);
sb.append(']');
return sb.toString();
}
*/
/*
/**********************************************************
/* Internal methods
/**********************************************************
*/
private void _addSymbol(int hash, Name symbol)
{
if (_mainHashShared) { // always have to modify main entry
unshareMain();
}
// First, do we need to rehash?
if (_needRehash) {
rehash();
}
++_count;
/* Ok, enough about set up: now we need to find the slot to add
* symbol in:
*/
int ix = (hash & _mainHashMask);
if (_mainNames[ix] == null) { // primary empty?
_mainHash[ix] = (hash << 8);
if (_mainNamesShared) {
unshareNames();
}
_mainNames[ix] = symbol;
} else { // nope, it's a collision, need to spill over
/* How about spill-over area... do we already know the bucket
* (is the case if it's not the first collision)
*/
if (_collListShared) {
unshareCollision(); // also allocates if list was null
}
++_collCount;
int entryValue = _mainHash[ix];
int bucket = entryValue & 0xFF;
if (bucket == 0) { // first spill over?
if (_collEnd <= LAST_VALID_BUCKET) { // yup, still unshared bucket
bucket = _collEnd;
++_collEnd;
// need to expand?
if (bucket >= _collList.length) {
expandCollision();
}
} else { // nope, have to share... let's find shortest?
bucket = findBestBucket();
}
// Need to mark the entry... and the spill index is 1-based
_mainHash[ix] = (entryValue & ~0xFF) | (bucket + 1);
} else {
--bucket; // 1-based index in value
}
// And then just need to link the new bucket entry in
Bucket newB = new Bucket(symbol, _collList[bucket]);
_collList[bucket] = newB;
// but, be careful wrt attacks
_longestCollisionList = Math.max(newB.length(), _longestCollisionList);
if (_longestCollisionList > MAX_COLL_CHAIN_LENGTH) {
reportTooManyCollisions(MAX_COLL_CHAIN_LENGTH);
}
}
/* Ok. Now, do we need a rehash next time? Need to have at least
* 50% fill rate no matter what:
*/
{
int hashSize = _mainHash.length;
if (_count > (hashSize >> 1)) {
int hashQuarter = (hashSize >> 2);
/* And either strictly above 75% (the usual) or
* just 50%, and collision count >= 25% of total hash size
*/
if (_count > (hashSize - hashQuarter)) {
_needRehash = true;
} else if (_collCount >= hashQuarter) {
_needRehash = true;
}
}
}
}
private void rehash()
{
_needRehash = false;
// Note: since we'll make copies, no need to unshare, can just mark as such:
_mainNamesShared = false;
/* And then we can first deal with the main hash area. Since we
* are expanding linearly (double up), we know there'll be no
* collisions during this phase.
*/
int[] oldMainHash = _mainHash;
int len = oldMainHash.length;
int newLen = len+len;
/* 13-Mar-2010, tatu: Let's guard against OOME that could be caused by
* large documents with unique (or mostly so) names
*/
if (newLen > MAX_TABLE_SIZE) {
nukeSymbols();
return;
}
_mainHash = new int[newLen];
_mainHashMask = (newLen - 1);
Name[] oldNames = _mainNames;
_mainNames = new Name[newLen];
int symbolsSeen = 0; // let's do a sanity check
for (int i = 0; i < len; ++i) {
Name symbol = oldNames[i];
if (symbol != null) {
++symbolsSeen;
int hash = symbol.hashCode();
int ix = (hash & _mainHashMask);
_mainNames[ix] = symbol;
_mainHash[ix] = hash << 8; // will clear spill index
}
}
/* And then the spill area. This may cause collisions, although
* not necessarily as many as there were earlier. Let's allocate
* same amount of space, however
*/
int oldEnd = _collEnd;
if (oldEnd == 0) { // no prior collisions...
_longestCollisionList = 0;
return;
}
_collCount = 0;
_collEnd = 0;
_collListShared = false;
int maxColl = 0;
Bucket[] oldBuckets = _collList;
_collList = new Bucket[oldBuckets.length];
for (int i = 0; i < oldEnd; ++i) {
for (Bucket curr = oldBuckets[i]; curr != null; curr = curr._next) {
++symbolsSeen;
Name symbol = curr._name;
int hash = symbol.hashCode();
int ix = (hash & _mainHashMask);
int val = _mainHash[ix];
if (_mainNames[ix] == null) { // no primary entry?
_mainHash[ix] = (hash << 8);
_mainNames[ix] = symbol;
} else { // nope, it's a collision, need to spill over
++_collCount;
int bucket = val & 0xFF;
if (bucket == 0) { // first spill over?
if (_collEnd <= LAST_VALID_BUCKET) { // yup, still unshared bucket
bucket = _collEnd;
++_collEnd;
// need to expand?
if (bucket >= _collList.length) {
expandCollision();
}
} else { // nope, have to share... let's find shortest?
bucket = findBestBucket();
}
// Need to mark the entry... and the spill index is 1-based
_mainHash[ix] = (val & ~0xFF) | (bucket + 1);
} else {
--bucket; // 1-based index in value
}
// And then just need to link the new bucket entry in
Bucket newB = new Bucket(symbol, _collList[bucket]);
_collList[bucket] = newB;
maxColl = Math.max(maxColl, newB.length());
}
} // for (... buckets in the chain ...)
} // for (... list of bucket heads ... )
_longestCollisionList = maxColl;
if (symbolsSeen != _count) { // sanity check
throw new RuntimeException("Internal error: count after rehash "+symbolsSeen+"; should be "+_count);
}
}
/**
* Helper method called to empty all shared symbols, but to leave
* arrays allocated
*/
private void nukeSymbols()
{
_count = 0;
_longestCollisionList = 0;
Arrays.fill(_mainHash, 0);
Arrays.fill(_mainNames, null);
Arrays.fill(_collList, null);
_collCount = 0;
_collEnd = 0;
}
/**
* Method called to find the best bucket to spill a Name over to:
* usually the first bucket that has only one entry, but in general
* first one of the buckets with least number of entries
*/
private int findBestBucket()
{
Bucket[] buckets = _collList;
int bestCount = Integer.MAX_VALUE;
int bestIx = -1;
for (int i = 0, len = _collEnd; i < len; ++i) {
int count = buckets[i].length();
if (count < bestCount) {
if (count == 1) { // best possible
return i;
}
bestCount = count;
bestIx = i;
}
}
return bestIx;
}
/**
* Method that needs to be called, if the main hash structure
* is (may be) shared. This happens every time something is added,
* even if addition is to the collision list (since collision list
* index comes from lowest 8 bits of the primary hash entry)
*/
private void unshareMain()
{
final int[] old = _mainHash;
_mainHash = ArraysCompat.copyOf(old, old.length);
_mainHashShared = false;
}
private void unshareCollision()
{
Bucket[] old = _collList;
if (old == null) {
_collList = new Bucket[INITIAL_COLLISION_LEN];
} else {
_collList = ArraysCompat.copyOf(old, old.length);
}
_collListShared = false;
}
private void unshareNames()
{
final Name[] old = _mainNames;
_mainNames = ArraysCompat.copyOf(old, old.length);
_mainNamesShared = false;
}
private void expandCollision()
{
final Bucket[] old = _collList;
_collList = ArraysCompat.copyOf(old, old.length * 2);
}
/*
/**********************************************************
/* Constructing name objects
/**********************************************************
*/
private static Name constructName(int hash, String name, int q1, int q2)
{
if (q2 == 0) { // one quad only?
return new Name1(name, hash, q1);
}
return new Name2(name, hash, q1, q2);
}
private static Name constructName(int hash, String name, int[] quads, int qlen)
{
if (qlen < 4) { // Need to check for 3 quad one, can do others too
switch (qlen) {
case 1:
return new Name1(name, hash, quads[0]);
case 2:
return new Name2(name, hash, quads[0], quads[1]);
case 3:
return new Name3(name, hash, quads[0], quads[1], quads[2]);
default:
}
}
// Otherwise, need to copy the incoming buffer
int[] buf = new int[qlen];
for (int i = 0; i < qlen; ++i) {
buf[i] = quads[i];
}
return new NameN(name, hash, buf, qlen);
}
/*
/**********************************************************
/* Other helper methods
/**********************************************************
*/
/**
* @since 2.1
*/
protected void reportTooManyCollisions(int maxLen)
{
throw new IllegalStateException("Longest collision chain in symbol table (of size "+_count
+") now exceeds maximum, "+maxLen+" -- suspect a DoS attack based on hash collisions");
}
/*
/**********************************************************
/* Helper classes
/**********************************************************
*/
/**
* Immutable value class used for sharing information as efficiently
* as possible, by only require synchronization of reference manipulation
* but not access to contents.
*
* @since 2.1
*/
private final static class TableInfo
{
public final int count;
public final int mainHashMask;
public final int[] mainHash;
public final Name[] mainNames;
public final Bucket[] collList;
public final int collCount;
public final int collEnd;
public final int longestCollisionList;
public TableInfo(int count, int mainHashMask, int[] mainHash, Name[] mainNames,
Bucket[] collList, int collCount, int collEnd, int longestCollisionList)
{
this.count = count;
this.mainHashMask = mainHashMask;
this.mainHash = mainHash;
this.mainNames = mainNames;
this.collList = collList;
this.collCount = collCount;
this.collEnd = collEnd;
this.longestCollisionList = longestCollisionList;
}
public TableInfo(BytesToNameCanonicalizer src)
{
count = src._count;
mainHashMask = src._mainHashMask;
mainHash = src._mainHash;
mainNames = src._mainNames;
collList = src._collList;
collCount = src._collCount;
collEnd = src._collEnd;
longestCollisionList = src._longestCollisionList;
}
}
/**
*
*/
final static class Bucket
{
protected final Name _name;
protected final Bucket _next;
private final int _length;
Bucket(Name name, Bucket next)
{
_name = name;
_next = next;
_length = (next == null) ? 1 : next._length+1;
}
public int length() { return _length; }
public Name find(int hash, int firstQuad, int secondQuad)
{
if (_name.hashCode() == hash) {
if (_name.equals(firstQuad, secondQuad)) {
return _name;
}
}
for (Bucket curr = _next; curr != null; curr = curr._next) {
Name currName = curr._name;
if (currName.hashCode() == hash) {
if (currName.equals(firstQuad, secondQuad)) {
return currName;
}
}
}
return null;
}
public Name find(int hash, int[] quads, int qlen)
{
if (_name.hashCode() == hash) {
if (_name.equals(quads, qlen)) {
return _name;
}
}
for (Bucket curr = _next; curr != null; curr = curr._next) {
Name currName = curr._name;
if (currName.hashCode() == hash) {
if (currName.equals(quads, qlen)) {
return currName;
}
}
}
return null;
}
}
}