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package javax.ejb;

import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.*;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.*;

import java.util.concurrent.TimeUnit;

/**
 * Specifies the amount of time in a given time unit that a concurrent
 * access attempt should block before timing out.
 * <p>
 * This annotation may be applied to a stateful session bean or to a
 * singleton session bean that uses container managed concurrency.
 * <p>
 * By default, clients are allowed to make concurrent calls to a
 * stateful session object and the container is required to serialize
 * such concurrent requests.  The <code>AccessTimeout</code>
 * annotation is used to specify the amount of time a stateful session
 * bean request should block in the case that the bean instance
 * is already processing a different request.  Use of the
 * <code>AccessTimeout</code> annotation with a value of 0 specifies
 * to the container that concurrent client requests to a stateful
 * session bean are prohibited.
 * <p>
 * The <code>AccessTimeout</code> annotation can be specified on a
 * business method or a bean class.  If it is specified on a class, it
 * applies to all business methods of that class.  If it is specified
 * on both a class and on a business method of the class, the
 * method-level annotation takes precedence for the given method.
 * <p>
 * Access timeouts for a singleton session bean only apply to methods
 * eligible for concurrency locks.  The <code>AccessTimeout</code> annotation can
 * be specified on the singleton session bean class or on an eligible
 * method of the class.  If <code>AccessTimeout</code> is specified on
 * both a class and on a method of that class, the method-level annotation
 * takes precedence for the given method.
 * <p>
 * The semantics of the <code>value</code> element are as follows:
 * <ul>
 * <li>A value <code>></code> 0 indicates a timeout value in the units
 * specified by the <code>unit</code> element.
 * <li>A value of 0 means concurrent access is not permitted.
 * <li>A value of -1 indicates that the client request will block
 * indefinitely until forward progress it can proceed.
 * </ul>
 * Values less than -1 are not valid.
 *
 * @since EJB 3.1
 */
@Target({METHOD, TYPE})
@Retention(RUNTIME)
public @interface AccessTimeout {

    /**
     * The semantics of the <code>value</code> element are as follows:
     * <ul>
     * <li>A value <code>></code> 0 indicates a timeout value in the units
     * specified by the <code>unit</code> element.
     * <li>A value of 0 means concurrent access is not permitted.
     * <li>A value of -1 indicates that the client request will block
     * indefinitely until forward progress it can proceed.
     * </ul>
     * Values less than -1 are not valid.
     */
    long value();

    /**
     * Units used for the specified value.
     */
    TimeUnit unit() default TimeUnit.MILLISECONDS;

}