I would strongly recommend using the version in Guice wiki instead. It
appears that your scope only provides one type of instance, which is
not really a scope at all.
And you use DCL by locking on Injector.class which Scopes.SINGLETON
also locks on, this could cause unnecessary performance hits.
I suggested sometime ago that Guice singleton should probably not
synchronize on Injector.class, I reiterate that suggestion =D
Dhanji.
On Thu, Nov 20, 2008 at 8:41 AM, davide <[EMAIL PROTECTED]> wrote:
>
> Hi,
>
> some time ago I wrote my own implementation of custom scope (attached
> below) that, in order to cache objects, returns a Provider that keeps
> its cached instance (like com.google.inject.Scopes.SINGLETON).
>
> Today, looking at the wiki page I saw that the suggested
> implementation of custom scope maintain its own map for caching
> instances. Is this map needed? is my implementation broken?
>
> Thanks,
> Davide
>
>
> /**
> * Simple implementation of Guice scope, that admit a single active
> scope a time
> * and identify the lifespan of a scope with an object of type S.
> */
> public class SimpleScope<S> implements Scope {
>
> /**
> * A listener for the scope event [EMAIL PROTECTED] SimpleScope#end()}
> */
> public interface Listener {
> void scopeBegin(Object scopeId);
> void scopeEnd();
> }
>
> private S scopeId;
> private List<Listener> listeners;
>
> private final Provider<S> SCOPE_ID_PROVIDER = new Provider<S>() {
> public S get() {
> if (scopeId == null)
> throw new IllegalStateException("In "+SimpleScope.this+"
> requested
> value when inactive");
> return scopeId;
> }
> };
>
> protected <T> SimpleScope(SimpleScope<T> parentScope) {
> listeners = new ArrayList<Listener>();
> if (parentScope != null) {
> final Listener parentListener = new Listener() {
> public void scopeEnd() {
> if (scopeId != null)
> end();
> }
> public void scopeBegin(Object x) {}
> };
> parentScope.registerListener( parentListener );
> }
> }
>
> protected SimpleScope() {
> this(null);
> }
>
> public void registerListener(Listener listener) {
> listeners.add(listener);
> }
>
> public Provider<S> getActiveProvider() {
> return SCOPE_ID_PROVIDER;
> }
>
> public void begin(S scopeId) {
> if (scopeId == null)
> throw new NullPointerException("In "+this+" null scope
> identifier");
> if (this.scopeId != null)
> throw new IllegalStateException("In "+this+", attempted begin
> ("+scopeId+") when already active");
> this.scopeId = scopeId;
> for (Listener observer : listeners)
> observer.scopeBegin(scopeId);
> }
>
> public <T> Provider<T> scope(Key<T> key, Provider<T> creator) {
> SimpleScopeProvider<T> cachingProvider = new SimpleScopeProvider<T>
> (creator);
> listeners.add(cachingProvider);
> return cachingProvider;
> }
>
> public void end() {
> if (this.scopeId == null)
> throw new IllegalStateException("In "+this+", attempted end()
> when inactive");
> for (Listener observer : listeners)
> observer.scopeEnd();
> scopeId = null;
> }
>
> @Override
> public String toString() {
> StringBuilder sb = new StringBuilder(getClass().getName());
> if (scopeId != null)
> sb.append('(').append(scopeId).append(')');
> return sb.toString();
> }
> }
>
> /**
> * Caching provider used in SimpleScope
> * @author davide
> */
> class SimpleScopeProvider<T> implements Provider<T>,
> SimpleScope.Listener {
>
> private final Provider<T> creator;
> private volatile T instance;
>
> public SimpleScopeProvider(Provider<T> creator) {
> this.creator = creator;
> }
>
> public T get() {
> if (instance == null) {
> // see com.google.inject.Scopes.SINGLETON
> synchronized (Injector.class) {
> if (instance == null) {
> instance = creator.get();
> }
> }
> }
> return instance;
> }
>
> public void scopeBegin(Object scopeId) {
> T i = instance;
> if (i instanceof SimpleScope.Listener)
> ((SimpleScope.Listener) i).scopeBegin(scopeId);
> }
>
> public void scopeEnd() {
> // TODO check if any race condition may occur
> T i = instance;
> if (i instanceof SimpleScope.Listener)
> ((SimpleScope.Listener) i).scopeEnd();
> instance = null;
>
> }
>
> public String toString() {
> return creator.toString();
> }
> }
>
> >
>
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