api/src/main/java/org/apache/edgent/execution/services/RuntimeServices.java

/*
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regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
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  http://www.apache.org/licenses/LICENSE-2.0

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*/
package org.apache.edgent.execution.services;

/**
 * At runtime a container provides services to
 * executing elements such as oplets and functions.
 * 
 * <P>
 * Services, providers and applications can optionally store
 * preferences (configuration information) using a {@code java.util.pref.Preferences}
 * instance registered as a service. Any provider may optionally register
 * a root {@code Preferences} node. Once a provider registers
 * a {@code Preferences} node, preferences will
 * be saved across reboots of the provider and/or JVM if the underlying
 * {@code Preferences} implementation supports it.
 * 
 * <BR>
 * Services and application code can store keys
 * in the root {@code Preferences} node or create child nodes
 * as required.
 * <pre>
 * <code>
 * Preferences prefs = rs.getService(Preferences.class);
 * if (prefs != null) {
 *     prefs.put("threshold", 3);
 * }
 * </code>
 * </pre>
 *
 */
public interface RuntimeServices {
    
    /**
     * Get a service for this invocation.
     * <P>
     * These services must be provided by all implementations:
     * </P>
     * <UL>
     * <LI>
     * {@code java.util.concurrent.ThreadFactory} - Thread factory, runtime code should
     * create new threads using this factory.
     * </LI>
     * <LI>
     * {@code java.util.concurrent.ScheduledExecutorService} - Scheduler, runtime code should
     * execute asynchronous and repeating tasks using this scheduler. 
     * </LI>
     * </UL>
     * 
     * @param <T> service class type
     * @param serviceClass Type of the service required.
     * @return Service of type implementing {@code serviceClass} if the 
     *      container this invocation runs in supports that service, 
     *      otherwise {@code null}.
     */
    <T> T getService(Class<T> serviceClass);
}