/**
* Reorgainizes all the key/value pairs in the hash table to accomodate the new size.
*
* @param newNrBuckets The new size.
*/
private void rehash(int newNrBuckets) throws IOException {
if (newNrBuckets == nrBuckets) return;
int oldNrBuckets = nrBuckets;
nrBuckets = newNrBuckets;
// Iterate over the buckets, moving items to their correct locations.
for (int bucket = 0; ; ++bucket) {
long value;
if ((value = getValue(bucket)) != 0) {
// This bucket is in use.
long offset = (long) bucket * 4;
int hashCode = hashFile.getInt(offset);
int destBucket = calcBucket(hashCode);
// Work out where the item belongs. Abort if it ends up back here.
while (destBucket != bucket) {
if (getValue(destBucket) == 0) {
// Found an empty bucket. Move the item here.
long destOffset = (long) destBucket * 4;
hashFile.putInt(destOffset, hashCode);
hashFile.putInt(destOffset + 1, hashFile.getInt(offset + 1));
hashFile.putLong((long) destBucket * 2 + 1, value);
// Clear the old bucket.
hashFile.putLong((long) bucket * 2 + 1, 0);
break;
}
// Try the next bucket.
destBucket = (destBucket + 1) % nrBuckets;
}
} else {
// An empty bucket.
// Stop if we have processed all of the old buckets.
// NOTE: We potentially process more than oldNrBuckets buckets
// so that we pick up any items that clashed and were bounced
// past the end of this range 0..(oldNrBuckets-1).
if (bucket >= oldNrBuckets) break;
}
}
}
/**
* Returns the long associated with the String or 0 if there is no long associated with the
* string. If newValue is not equal to 0 then this becomes the new value associated with the
* string.
*
* @param str the String.
* @param newValue if not equal to 0, the new value to be associated with the string.
* @return the long currently associated with the String or 0 if there is no long associated with
* the string.
* @throws IOException if an I/O error occurs or the hash table is full.
*/
public long getAndPut(String str, long newValue) throws IOException {
if (str == null) {
throw new IllegalArgumentException("str is null");
}
if (newValue == 0) {
Long l = cache.get(str);
if (l != null) {
return l.longValue();
}
}
int hashCode = str.hashCode();
int startBucket = calcBucket(hashCode);
int bucket = startBucket;
long value;
// Try buckets until we find the correct string or an empty bucket.
while ((value = getValue(bucket)) != 0) {
// Check the hash code.
long offset = (long) bucket * 4;
if (hashCode == hashFile.getInt(offset)) {
// Fetch the string and compare with the target string.
String bucketStr = readString(hashFile.getUInt(offset + 1));
if (str.equals(bucketStr)) {
if (newValue != 0) {
hashFile.putLong((long) bucket * 2 + 1, newValue);
// Add the new value to the cache.
cache.put(str, newValue);
} else {
// Add the value to the cache.
cache.put(str, value);
}
return value;
}
}
// Try the next bucket.
bucket = (bucket + 1) % nrBuckets;
if (bucket == startBucket) {
throw new IOException("Hash table full");
}
}
if (newValue != 0) {
// Add the new value to the cache.
cache.put(str, newValue);
// Add a new hash bucket.
long bucketOffset = (long) bucket * 4;
hashFile.putInt(bucketOffset, hashCode);
hashFile.putUInt(bucketOffset + 1, writeString(str));
hashFile.putLong((long) bucket * 2 + 1, newValue);
++nrUsedBuckets;
if (nrUsedBuckets >= (int) (nrBuckets * REHASH_LIMIT)) {
rehash(findPrime(nrBuckets));
}
}
return 0;
}