Package org.postgresql.core

Class AsciiStringInterner

java.lang.Object

org.postgresql.core.AsciiStringInterner

final class AsciiStringInterner
extends Object

Provides the canonicalization/interning of String instances which contain only ascii characters, keyed by the byte[] representation (in ascii).

The values are stored in SoftReferences, allowing them to be garbage collected if not in use and there is memory pressure.

NOTE: Instances are safe for concurrent use.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	AsciiStringInterner.BaseKey
private static final class	AsciiStringInterner.Key	Instance used for inserting values into the cache.
private final class	AsciiStringInterner.StringReference	Custom SoftReference implementation which maintains a reference to the key in the cache, which allows aggressive cleaning when garbage collector collects the String instance.
private static class	AsciiStringInterner.TempKey	Only used for lookups, never to actually store entries.

Field Summary

Fields

Modifier and Type	Field	Description
(package private) final ConcurrentMap<AsciiStringInterner.BaseKey,SoftReference<String>>	cache	Contains the canonicalized values, keyed by the ascii byte[].
(package private) final ReferenceQueue<String>	refQueue	Used for Reference as values in cache.

Constructor Summary

Constructors

Constructor	Description
AsciiStringInterner()

Method Summary

Modifier and Type	Method	Description
(package private) static boolean	arrayEquals(byte[] a, int aOffset, int aLength, byte[] b, int bOffset, int bLength)	Performs equality check between a and b (with corresponding offset/length values).
private void	cleanQueue()	Process any entries in refQueue to purge from the cache.
String	getString(byte[] bytes, int offset, int length, Encoding encoding)	Produces a String instance for the given bytes.
String	getStringIfPresent(byte[] bytes, int offset, int length, Encoding encoding)	Produces a String instance for the given bytes.
private static int	hashKey(byte[] bytes, int offset, int length)	Generates a hash value for the relevant entries in bytes as long as all values are ascii (>= 0).
boolean	putString(String val)	Preemptively populates a value into the cache.
String	toString()

Methods inherited from class java.lang.Object

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

Field Details

cache

final ConcurrentMap<AsciiStringInterner.BaseKey,SoftReference<String>> cache

Contains the canonicalized values, keyed by the ascii byte[].

refQueue

final ReferenceQueue<String> refQueue

Used for Reference as values in cache.

Constructor Details

AsciiStringInterner

AsciiStringInterner()

Method Details

putString

public boolean putString(String val)

Preemptively populates a value into the cache. This is intended to be used with String constants which are frequently used. While this can work with other String values, if val is ever garbage collected, it will not be actively removed from this instance.

Parameters:

val - The value to intern. Must not be null.

Returns:

Indication if val is an ascii String and placed into cache.

getString

public String getString(byte[] bytes,
 int offset,
 int length,
 Encoding encoding)
                 throws IOException

Produces a String instance for the given bytes. If all are valid ascii (i.e. >= 0) either an existing value will be returned, or the newly created String will be stored before being returned.

If non-ascii bytes are discovered, the encoding will be used to decode and that value will be returned (but not stored).

Parameters:

bytes - The bytes of the String. Must not be null.

offset - Offset into bytes to start.

length - The number of bytes in bytes which are relevant.

encoding - To use if non-ascii bytes seen.

Returns:

Decoded String from bytes.

Throws:

IOException - If error decoding from Encoding.

getStringIfPresent

public String getStringIfPresent(byte[] bytes,
 int offset,
 int length,
 Encoding encoding)
                          throws IOException

Produces a String instance for the given bytes.

If all are valid ascii (i.e. >= 0) and a corresponding String value exists, it will be returned. If no value exists, a String will be created, but not stored.

If non-ascii bytes are discovered, the encoding will be used to decode and that value will be returned (but not stored).

Parameters:

bytes - The bytes of the String. Must not be null.

offset - Offset into bytes to start.

length - The number of bytes in bytes which are relevant.

encoding - To use if non-ascii bytes seen.

Returns:

Decoded String from bytes.

Throws:

IOException - If error decoding from Encoding.

cleanQueue

private void cleanQueue()

Process any entries in refQueue to purge from the cache.

See Also:

• AsciiStringInterner.StringReference.dispose()

hashKey

private static int hashKey(byte[] bytes,
 int offset,
 int length)

Generates a hash value for the relevant entries in bytes as long as all values are ascii (>= 0).

Returns:

hash code for relevant bytes, or 0 if non-ascii bytes present.

arrayEquals

static boolean arrayEquals(byte[] a,
 int aOffset,
 int aLength,
 byte[] b,
 int bOffset,
 int bLength)

Performs equality check between a and b (with corresponding offset/length values).

The static boolean equals(byte[].class, int, int, byte[], int, int method in Arrays is optimized for longer byte[] instances than is expected to be seen here.

toString

public String toString()

Overrides:

toString in class Object