nonapi.io.github.classgraph.concurrency

Class SingletonMap<K,V,E extends java.lang.Exception>

java.lang.Object

nonapi.io.github.classgraph.concurrency.SingletonMap<K,V,E>

Type Parameters:

K - The key type.

V - The value type.

E - the element type

public abstract class SingletonMap<K,V,E extends java.lang.Exception>
extends java.lang.Object

A map from keys to singleton instances. Allows you to create object instance singletons and add them to a ConcurrentMap on demand, based on a key value. Works the same as concurrentMap.computeIfAbsent(key, key -> newInstance(key)), except that it also works on JDK 7.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	SingletonMap.NewInstanceException Thrown when newInstance(Object, LogNode) throws an exception.
static class	SingletonMap.NullSingletonException Thrown when newInstance(Object, LogNode) returns null.

Constructor Summary

Constructors

Constructor and Description
SingletonMap()

Method Summary

Modifier and Type	Method and Description
void	clear() Clear the map.
java.util.List<java.util.Map.Entry<K,V>>	entries() Get the map entries.
V	get(K key, LogNode log) Check if the given key is in the map, and if so, return the value of newInstance(Object, LogNode) for that key, or block on the result of newInstance(Object, LogNode) if another thread is currently creating the new instance.
boolean	isEmpty() Returns true if the map is empty.
abstract V	newInstance(K key, LogNode log) Construct a new singleton instance.
V	remove(K key) Remove the singleton for a given key.
java.util.List<V>	values() Get all valid singleton values in the map.

Methods inherited from class java.lang.Object

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

Constructor Detail

SingletonMap

public SingletonMap()

Method Detail

newInstance

public abstract V newInstance(K key,
                              LogNode log)
                       throws E extends java.lang.Exception,
                              java.lang.InterruptedException

Construct a new singleton instance.

Parameters:

key - The key for the singleton.

log - The log.

Returns:

The singleton instance. This method must either return a non-null value, or throw an exception of type E.

Throws:

E - If something goes wrong while instantiating the new object instance.

java.lang.InterruptedException - if the thread was interrupted while instantiating the singleton.

E extends java.lang.Exception

get

public V get(K key,
             LogNode log)
      throws E extends java.lang.Exception,
             java.lang.InterruptedException,
             SingletonMap.NullSingletonException,
             SingletonMap.NewInstanceException

Check if the given key is in the map, and if so, return the value of newInstance(Object, LogNode) for that key, or block on the result of newInstance(Object, LogNode) if another thread is currently creating the new instance. If the given key is not currently in the map, store a placeholder in the map for this key, then run newInstance(Object, LogNode) for the key, store the result in the placeholder (which unblocks any other threads waiting for the value), and then return the new instance.

Parameters:

key - The key for the singleton.

log - The log.

Returns:

The non-null singleton instance, if newInstance(Object, LogNode) returned a non-null instance on this call or a previous call, otherwise throws NullPointerException if this call or a previous call to newInstance(Object, LogNode) returned null.

Throws:

E - If newInstance(Object, LogNode) threw an exception.

java.lang.InterruptedException - if the thread was interrupted while waiting for the singleton to be instantiated by another thread.

SingletonMap.NullSingletonException - if newInstance(Object, LogNode) returned null.

SingletonMap.NewInstanceException - if newInstance(Object, LogNode) threw an exception.

E extends java.lang.Exception

values

public java.util.List<V> values()
                         throws java.lang.InterruptedException

Get all valid singleton values in the map.

Returns:

the singleton values in the map, skipping over any value for which newInstance() threw an exception or returned null.

Throws:

java.lang.InterruptedException - If getting the values was interrupted.

isEmpty

public boolean isEmpty()

Returns true if the map is empty.

Returns:

true, if the map is empty

entries

public java.util.List<java.util.Map.Entry<K,V>> entries()
                                                 throws java.lang.InterruptedException

Get the map entries.

Returns:

the map entries.

Throws:

java.lang.InterruptedException - if interrupted.

remove

public V remove(K key)
         throws java.lang.InterruptedException

Remove the singleton for a given key.

Parameters:

key - the key

Returns:

the old singleton from the map, if one was present, otherwise null.

Throws:

java.lang.InterruptedException - if interrupted.

clear

public void clear()

Clear the map.