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/*******************************************************************************
 * Copyright (c) 2010-present Sonatype, Inc.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   Stuart McCulloch (Sonatype, Inc.) - initial API and implementation
 *******************************************************************************/
package org.eclipse.sisu.bean;

import java.util.ArrayList;

import com.google.inject.Binder;
import com.google.inject.Module;
import com.google.inject.Scopes;
import com.google.inject.matcher.Matcher;
import com.google.inject.matcher.Matchers;
import com.google.inject.spi.BindingScopingVisitor;
import com.google.inject.spi.DefaultBindingScopingVisitor;

/**
 * Schedules safe activation of beans even when cyclic dependencies are involved.
* Takes advantage of the new Guice ProvisionListener SPI, if available at runtime. */ public abstract class BeanScheduler { // ---------------------------------------------------------------------- // Static initialization // ---------------------------------------------------------------------- static { Object cycleActivator; Object candidateCycle = new Object(); Object cycleConfirmed = new Object(); try { // extra check in case we have both old and new versions of guice overlapping on the runtime classpath Binder.class.getMethod( "bindListener", Matcher.class, com.google.inject.spi.ProvisionListener[].class ); // allow cycle detection to be turned off completely final String detectCycles = System.getProperty( "sisu.detect.cycles" ); if ( "false".equalsIgnoreCase( detectCycles ) ) { cycleActivator = null; } else { cycleActivator = new CycleActivator(); } // support use of the old 'pessimistic' approach if ( "pessimistic".equalsIgnoreCase( detectCycles ) ) { candidateCycle = cycleConfirmed; } } catch ( final Exception e ) { cycleActivator = null; } catch ( final LinkageError e ) { cycleActivator = null; } CYCLE_ACTIVATOR = cycleActivator; CANDIDATE_CYCLE = candidateCycle; CYCLE_CONFIRMED = cycleConfirmed; } // ---------------------------------------------------------------------- // Constants // ---------------------------------------------------------------------- static final Object CYCLE_ACTIVATOR; static final Object CANDIDATE_CYCLE; static final Object CYCLE_CONFIRMED; /** * Enables deferred activation of component cycles, only needed in legacy systems like Plexus. */ public static final Module MODULE = new Module() { public void configure( final Binder binder ) { if ( null != CYCLE_ACTIVATOR ) { binder.bindListener( Matchers.any(), (com.google.inject.spi.ProvisionListener) CYCLE_ACTIVATOR ); } } }; // ---------------------------------------------------------------------- // Implementation fields // ---------------------------------------------------------------------- static final ThreadLocal pendingHolder = new ThreadLocal(); // ---------------------------------------------------------------------- // Public methods // ---------------------------------------------------------------------- /** * Detects if a dependency cycle exists and activation needs to be deferred. */ public static void detectCycle( final Object value ) { if ( null != CYCLE_ACTIVATOR && Scopes.isCircularProxy( value ) ) { final Object[] holder = pendingHolder.get(); if ( null != holder ) { final Object pending = holder[0]; if ( CANDIDATE_CYCLE.equals( pending ) ) { holder[0] = CYCLE_CONFIRMED; } } } } /** * Schedules activation of the given bean at the next safe activation point. * * @param bean The managed bean */ public final void schedule( final Object bean ) { if ( null != CYCLE_ACTIVATOR ) { final Object[] holder = pendingHolder.get(); if ( null != holder ) { final Object pending = holder[0]; if ( CYCLE_CONFIRMED.equals( pending ) ) { holder[0] = new Pending( bean ); return; // will be activated later } else if ( pending instanceof Pending ) { ( (Pending) pending ).add( bean ); return; // will be activated later } } } activate( bean ); // no ProvisionListener, so activate immediately } // ---------------------------------------------------------------------- // Customizable methods // ---------------------------------------------------------------------- /** * Customized activation of the given bean. * * @param bean The bean to activate */ protected abstract void activate( final Object bean ); // ---------------------------------------------------------------------- // Implementation types // ---------------------------------------------------------------------- /** * Collects pending beans waiting for activation. */ @SuppressWarnings( "serial" ) private final class Pending extends ArrayList { Pending( final Object bean ) { add( bean ); } /** * Activates pending beans in order of registration, that is in the order they finished injection. */ public void activate() { for ( int i = 0, size = size(); i < size; i++ ) { BeanScheduler.this.activate( get( i ) ); } } } /** * Listens to provisioning events in order to determine safe activation points. */ static final class CycleActivator implements com.google.inject.spi.ProvisionListener { private static final BindingScopingVisitor IS_SCOPED = new DefaultBindingScopingVisitor() { @Override public Boolean visitNoScoping() { return Boolean.FALSE; } @Override protected Boolean visitOther() { return Boolean.TRUE; } }; public void onProvision( final ProvisionInvocation pi ) { // Only scoped dependencies like singletons are candidates for dependency cycles if ( Boolean.TRUE.equals( pi.getBinding().acceptScopingVisitor( IS_SCOPED ) ) ) { Object[] holder = pendingHolder.get(); if ( null == holder ) { pendingHolder.set( holder = new Object[1] ); } if ( null == holder[0] ) { final Object pending; holder[0] = CANDIDATE_CYCLE; try { pi.provision(); // may involve nested calls/cycles } finally { pending = holder[0]; holder[0] = null; } if ( pending instanceof Pending ) { ( (Pending) pending ).activate(); } } } } } }