【算法】6、指数退避算法

            Do some asynchronous operation.·
retries = 0
DO
    wait for (2^retries * 100) milliseconds
    status = Get the result of the asynchronous operation.
    IF status = SUCCESS
        retry = false
    ELSE IF status = NOT_READY
        retry = true
    ELSE IF status = THROTTLED
        retry = true
    ELSE
        Some other error occurred, so stop calling the API.
        retry = false
    END IF
    retries = retries + 1
WHILE (retry AND (retries < MAX_RETRIES))

            public
            enum
             Results {
    SUCCESS, 
    NOT_READY, 
    THROTTLED, 
    SERVER_ERROR
}


            /*
            
 * Performs an asynchronous operation, then polls for the result of the
 * operation using an incremental delay.
 
            */
            public
            static
            void
             doOperationAndWaitForResult() {
    
            try
             {
        
            //
             Do some asynchronous operation.
            long token = asyncOperation();
        int retries = 0;
        boolean retry = false;
        do {
            long waitTime = Math.min(getWaitTimeExp(retries), MAX_WAIT_INTERVAL);
            System.out.print(waitTime + "\n");
            // Wait for the result.            Thread.sleep(waitTime);
            // Get the result of the asynchronous operation.
            Results result = getAsyncOperationResult(token);
            if (Results.SUCCESS == result) {
                retry = false;
            } elseif (Results.NOT_READY == result) {
                retry = true;
            } elseif (Results.THROTTLED == result) {
                retry = true;
            } elseif (Results.SERVER_ERROR == result) {
                retry = true;
            }
            else {
                // Some other error occurred, so stop calling the API.
                retry = false;
            }
        } while (retry && (retries++ < MAX_RETRIES));
    }
    catch (Exception ex) {
    }
}

/*
 * Returns the next wait interval, in milliseconds, using an exponential
 * backoff algorithm.
 */publicstaticlong getWaitTimeExp(int retryCount) {
    long waitTime = ((long) Math.pow(2, retryCount) * 100L);
    return waitTime;
}