調(diào)用close方法后,此時是有可能存在未處理完的消息的；然后代碼會運行到下一個while死循環(huán), 如果客戶端沒有手動設(shè)置強(qiáng)制關(guān)閉, 則需要繼續(xù)處理未處理后的消息; 如果設(shè)置了強(qiáng)制關(guān)閉, 則表示客戶端丟棄未處理完的消息。

 /**
     * The main run loop for the sender thread
     */
    public void run() {
        log.debug("Starting Kafka producer I/O thread.");

        // main loop, runs until close is called
        while (running) {
            try {
                run(time.milliseconds());
            } catch (Exception e) {
                log.error("Uncaught error in kafka producer I/O thread: ", e);
            }
        }

        log.debug("Beginning shutdown of Kafka producer I/O thread, sending remaining records.");

        // okay we stopped accepting requests but there may still be
        // requests in the accumulator or waiting for acknowledgment,
        // wait until these are completed.
        while (!forceClose && (this.accumulator.hasUndrained() || this.client.inFlightRequestCount() > 0)) {
            try {
                run(time.milliseconds());
            } catch (Exception e) {
                log.error("Uncaught error in kafka producer I/O thread: ", e);
            }
        }
        if (forceClose) {
            // We need to fail all the incomplete batches and wake up the threads waiting on
            // the futures.
            log.debug("Aborting incomplete batches due to forced shutdown");
            this.accumulator.abortIncompleteBatches();
        }
        try {
            this.client.close();
        } catch (Exception e) {
            log.error("Failed to close network client", e);
        }

        log.debug("Shutdown of Kafka producer I/O thread has completed.");
    }