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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * accompanied this code).
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package com.sun.tools.internal.xjc.reader;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.HashMap;
import java.util.Map;

import com.sun.tools.internal.xjc.ErrorReceiver;
import com.sun.tools.internal.xjc.model.Model;

Holds all the binding related singleton components in a "ring",
and let you access those components, creating them as necessary.
 A Ring is local to a thread, and only one instanceof Ring can be active at any given time. Use begin() and end(Ring) to start/end a ring scope. Inside a scope, use get() to obtain the instance. 
 When a Model is built by the reader, an active Ring scope is assumed. 
Components in Ring

Depending on the schema language we are dealing with, different
components are in the model. But at least the following components
are in the ring.

 
ErrorReceiver 
Author:
Kohsuke Kawaguchi/**
 * Holds all the binding related singleton components in a "ring",
 * and let you access those components, creating them as necessary.
 *
 * <p>
 * A {@link Ring} is local to a thread,
 * and only one instanceof {@link Ring} can be active at any given time.
 *
 * Use {@link #begin()} and {@link #end(Ring)} to start/end a ring scope.
 * Inside a scope, use {@link #get()} to obtain the instance.
 *
 * <p>
 * When a {@link Model} is built by the reader, an active {@link Ring} scope
 * is assumed.
 *
 *
 * <h2>Components in Ring</h2>
 * <p>
 * Depending on the schema language we are dealing with, different
 * components are in the model. But at least the following components
 * are in the ring.
 *
 * <ul>
 *  <li>{@link ErrorReceiver}
 * </ul>
 *
 * @author Kohsuke Kawaguchi
 */
public final class Ring {

    private final Map<Class,Object> components = new HashMap<Class,Object>();

    private static final ThreadLocal<Ring> instances = new ThreadLocal<Ring>();

    private Ring() {}

    public static <T> void add( Class<T> clazz, T instance ) {
        assert !get().components.containsKey(clazz);
        get().components.put(clazz,instance);
    }

    public static <T> void add( T o ) {
        add((Class<T>)o.getClass(),o);
    }

    public static <T> T get( Class<T> key ) {
        T t = (T)get().components.get(key);
        if(t==null) {
            try {
                Constructor<T> c = key.getDeclaredConstructor();
                c.setAccessible(true);
                t = c.newInstance();
                if(!get().components.containsKey(key))
                    // many components register themselves.
                    add(key,t);
            } catch (InstantiationException e) {
                throw new Error(e);
            } catch (IllegalAccessException e) {
                throw new Error(e);
            } catch (NoSuchMethodException e) {
                throw new Error(e);
            } catch (InvocationTargetException e) {
                throw new Error(e);
            }
        }

        assert t!=null;
        return t;
    }

    
A Ring instance is associated with a thread. /**
     * A {@link Ring} instance is associated with a thread.
     */
    public static Ring get() {
        return instances.get();
    }

    
Starts a new scope.
/**
     * Starts a new scope.
     */
    public static Ring begin() {
        Ring r = null;
        synchronized (instances) {
            r = instances.get();
            instances.set(new Ring());
        }
        return r;
    }

    
Ends a scope.
/**
     * Ends a scope.
     */
    public static void end(Ring old) {
        synchronized (instances) {
            instances.remove();
            instances.set(old);
        }
    }
}