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Apache Jena Fuseki server Kafka connector
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.kafka.clients.consumer.internals;

import org.apache.kafka.common.utils.ExponentialBackoff;
import org.apache.kafka.common.utils.LogContext;
import org.slf4j.Logger;

class RequestState {

    private final Logger log;
    protected final String owner;
    final static int RETRY_BACKOFF_EXP_BASE = 2;
    final static double RETRY_BACKOFF_JITTER = 0.2;
    protected final ExponentialBackoff exponentialBackoff;
    protected long lastSentMs = -1;
    protected long lastReceivedMs = -1;
    protected int numAttempts = 0;
    protected long backoffMs = 0;
    private boolean requestInFlight = false;

    public RequestState(final LogContext logContext,
                        final String owner,
                        final long retryBackoffMs,
                        final long retryBackoffMaxMs) {
        this.log = logContext.logger(RequestState.class);
        this.owner = owner;
        this.exponentialBackoff = new ExponentialBackoff(
                retryBackoffMs,
                RETRY_BACKOFF_EXP_BASE,
                retryBackoffMaxMs,
                RETRY_BACKOFF_JITTER);
    }

    // Visible for testing
    RequestState(final LogContext logContext,
                 final String owner,
                 final long retryBackoffMs,
                 final int retryBackoffExpBase,
                 final long retryBackoffMaxMs,
                 final double jitter) {
        this.log = logContext.logger(RequestState.class);
        this.owner = owner;
        this.exponentialBackoff = new ExponentialBackoff(
                retryBackoffMs,
                retryBackoffExpBase,
                retryBackoffMaxMs,
                jitter);
    }

    /**
     * Reset request state so that new requests can be sent immediately
     * and the backoff is restored to its minimal configuration.
     */
    public void reset() {
        this.requestInFlight = false;
        this.lastSentMs = -1;
        this.lastReceivedMs = -1;
        this.numAttempts = 0;
        this.backoffMs = exponentialBackoff.backoff(0);
    }

    public boolean canSendRequest(final long currentTimeMs) {
        if (requestInFlight()) {
            log.trace("An inflight request already exists for {}", this);
            return false;
        }

        long remainingBackoffMs = remainingBackoffMs(currentTimeMs);

        if (remainingBackoffMs <= 0) {
            return true;
        } else {
            log.trace("{} ms remain before another request should be sent for {}", remainingBackoffMs, this);
            return false;
        }
    }

    /**
     * @return True if no response has been received after the last send, indicating that there
     * is a request in-flight.
     */
    public boolean requestInFlight() {
        return requestInFlight;
    }

    public void onSendAttempt(final long currentTimeMs) {
        this.requestInFlight = true;

        // Here we update the timer everytime we try to send a request.
        this.lastSentMs = currentTimeMs;
    }

    /**
     * Callback invoked after a successful send. This resets the number of attempts
     * to 0, but the minimal backoff will still be enforced prior to allowing a new
     * send. To send immediately, use {@link #reset()}.
     *
     * @param currentTimeMs Current time in milliseconds
     */
    public void onSuccessfulAttempt(final long currentTimeMs) {
        this.requestInFlight = false;
        this.lastReceivedMs = currentTimeMs;
        this.backoffMs = exponentialBackoff.backoff(0);
        this.numAttempts = 0;
    }

    /**
     * Callback invoked after a failed send. The number of attempts
     * will be incremented, which may increase the backoff before allowing
     * the next send attempt.
     *
     * @param currentTimeMs Current time in milliseconds
     */
    public void onFailedAttempt(final long currentTimeMs) {
        this.requestInFlight = false;
        this.lastReceivedMs = currentTimeMs;
        this.backoffMs = exponentialBackoff.backoff(numAttempts);
        this.numAttempts++;
    }

    long remainingBackoffMs(final long currentTimeMs) {
        long timeSinceLastReceiveMs = currentTimeMs - this.lastReceivedMs;
        return Math.max(0, backoffMs - timeSinceLastReceiveMs);
    }

    /**
     * This method appends the instance variables together in a simple String of comma-separated key value pairs.
     * This allows subclasses to include these values and not have to duplicate each variable, helping to prevent
     * any variables from being omitted when new ones are added.
     *
     * @return String version of instance variables.
     */
    protected String toStringBase() {
        return "owner='" + owner + '\'' +
                ", exponentialBackoff=" + exponentialBackoff +
                ", lastSentMs=" + lastSentMs +
                ", lastReceivedMs=" + lastReceivedMs +
                ", numAttempts=" + numAttempts +
                ", backoffMs=" + backoffMs +
                ", requestInFlight=" + requestInFlight;
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + "{" + toStringBase() + '}';
    }
}