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package org.glassfish.config.support;

import org.jvnet.hk2.annotations.Contract;

import java.io.IOException;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.locks.Lock;

/**
 * Service to lock the configuration elements for a particular domain
 * configuration. All changes to the domain configuration changes
 * being the domain.xml or the security artifacts must go through
 * this service to ensure proper synchronization.
 *
 * The access gate must be implemented using a read-write locking
 * where multiple users can access in read mode the configuration
 * while a write access requires a exclusive lock.
 *
 * A try {...} finally {...} block should be used to ensure the
 * Lock returned for access is released when the access to the
 * configuration is not needed any longer.
 *
 * @author Jerome Dochez
 */
@Contract
public interface ConfigurationAccess {

    /**
     * Wait and return an read access {@link Lock} to the configuration
     * elements. Once the lock is returned, other threads can access
     * the configuration is read mode, but no thread can access it in
     * write mode.
     *
     * The lock instance must be released in the same thread that
     * obtained it.
     *
     * @return the read access lock to be released once the
     * configuration access is not needed any longer.
     * @throws IOException if the configuration cannot be accessed
     * due to a file access error.
     * @throws TimeoutException if the lock cannot be obtained
     * before the system defined time out runs out.
     */
    public Lock accessRead() throws IOException, TimeoutException;

    /**
     * Wait and return an exclusive write access {@link Lock} to the configuration
     * elements. Once the lock is returned, no other thread can
     * access the configuration is read or write mode.
     *
     * The lock instance must be released in the same thread that
     * obtained it.
     *
     * @return the read access lock to be released once the
     * configuration access is not needed any longer.
     * @throws IOException if the configuration cannot be accessed
     * due to a file access error.
     * @throws TimeoutException if the lock cannot be obtained
     * before the system defined time out runs out.
     */

    public Lock accessWrite() throws IOException, TimeoutException;
}