// $Id: Promise.java,v 1.10 2005/07/17 11:33:58 chrislott Exp $package org.jgroups.util;import org.jgroups.TimeoutException;/** * Allows a thread to submit an asynchronous request and to wait for the result. The caller may choose to check * for the result at a later time, or immediately and it may block or not. Both the caller and responder have to * know the promise. * @author Bela Ban */public class Promise {    Object result=null;    boolean hasResult=false;    /**     * Blocks until a result is available, or timeout milliseconds have elapsed     * @param timeout     * @return An object     * @throws TimeoutException. If a timeout occurred (implies that timeout > 0)     */    public Object getResultWithTimeout(long timeout) throws TimeoutException {        synchronized(this) {            try {                return _getResultWithTimeout(timeout);            }            finally {                notifyAll();            }        }    }    /**     * Blocks until a result is available, or timeout milliseconds have elapsed. Needs to be called with     * a lock held on 'this'     * @param timeout     * @return An object     * @throws TimeoutException. If a timeout occurred (implies that timeout > 0)     */    private Object _getResultWithTimeout(long timeout) throws TimeoutException {        Object  ret=null;        long    time_to_wait=timeout, start;        boolean timeout_occurred=false;        start=System.currentTimeMillis();        while(hasResult == false) {            if(timeout <= 0) {                doWait();            }            else {                if(time_to_wait <= 0) {                    timeout_occurred=true;                    break; // terminate the while loop                }                else {                    doWait(time_to_wait);                    time_to_wait=timeout - (System.currentTimeMillis() - start);                }            }        }        ret=result;        result=null;        hasResult=false;        if(timeout_occurred)            throw new TimeoutException();        else            return ret;    }    public Object getResult() {        try {            return getResultWithTimeout(0);        }        catch(TimeoutException e) {            return null;        }    }    /**     * Returns the result, but never throws a TimeoutException; returns null instead.     * @param timeout     * @return Object     */    public Object getResult(long timeout) {        try {            return getResultWithTimeout(timeout);        }        catch(TimeoutException e) {            return null;        }    }    void doWait() {        try {wait();} catch(InterruptedException e) {}    }    void doWait(long timeout) {        try {wait(timeout);} catch(InterruptedException e) {}    }    /**     * Checks whether result is available. Does not block.     */    public boolean hasResult() {        synchronized(this) {            return hasResult;        }    }    /**     * Sets the result and notifies any threads     * waiting for it     */    public void setResult(Object obj) {        synchronized(this) {            result=obj;            hasResult=true;            notifyAll();        }    }    /**     * Causes all waiting threads to return     */    public void reset() {        synchronized(this) {            result=null;            hasResult=false;            notifyAll();        }    }    public String toString() {        return "hasResult=" + hasResult + ",result=" + result;    }}