Question

我正在尝试连接到MQTT代理。我想重试，以防我无法连接。我得到关于连接成功或失败的回调。

在阅读了多个retryWhen和处理异步回调的例子后，我将这段代码放在一起。如果我成功连接，它工作正常。此外，如果我从e.onError(throwable)同步拨打Flowable，它会重试3次。但如果我从回调的e.onError(throwable)方法中调用onFailure()，它会崩溃我的Android应用。

以下是代码：

RxJava链

createConnectionFlowable(client, options)
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    .retryWhen(createRetryFunction())
    .subscribe(createConsumer());

创建一个Flowable

private Flowable<String> createConnectionFlowable(final MqttAndroidClient client, final MqttConnectOptions options) {
    return Flowable.create(new FlowableOnSubscribe<String>() {

        public void subscribe(final FlowableEmitter<String> e) throws Exception {
                client.connect(options).setActionCallback(new IMqttActionListener() {
                    public void onSuccess(IMqttToken iMqttToken) { e.onComplete(); }
                    public void onFailure(IMqttToken iMqttToken, Throwable throwable) { e.onError(throwable); }
                });
        }
    }, BackpressureStrategy.BUFFER);
}

创建重试功能

private Function<Flowable<Throwable>, Publisher<?>> createRetryFunction() {
    return new Function<Flowable<Throwable>, Publisher<?>>() {

        public Publisher<?> apply(Flowable<Throwable> throwableFlowable) throws Exception {
            return throwableFlowable.zipWith(
                    Flowable.range(1, 3),
                    new BiFunction<Throwable, Integer, Integer>() {
                        public Integer apply(Throwable throwable, Integer integer) throws Exception { return integer; }
                    }
            )
            .flatMap(new Function<Integer, Publisher<?>>() {
                public Publisher<?> apply(Integer integer) throws Exception {
                    return Flowable.timer(integer, TimeUnit.SECONDS);
                }
            });
        }
    };
}

消费者：在这里做所有好事

private Consumer<String> createConsumer() {
    return new Consumer<String>() {
        public void accept(String s) throws Exception {
            Log.d(TAG, "accept: do important stuff here" + s);
        }
    };
}

错误日志

12-20 11:51:08.544 16769-16769/com.work.app D/MqttBridgeService: onFailure: connection unsuccessful
12-20 11:51:08.544 16769-16769/com.work.app D/MqttBridgeService: apply() called with: throwable = [Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /10.31.252.211 (port 1883) after 30000ms: isConnected failed: ECONNREFUSED (Connection refused)], integer = [1]
12-20 11:51:08.544 16769-16769/com.work.app D/MqttBridgeService: apply: delay retry by seconds:1
12-20 11:51:09.589 16769-16830/com.work.app D/AlarmPingSender: Unregister alarmreceiver to MqttServicepaho837944119000
12-20 11:51:09.600 16769-16831/com.work.app D/AlarmPingSender: Unregister alarmreceiver to MqttServicepaho837944119000
12-20 11:51:09.606 16769-16769/com.work.app D/MqttBridgeService: onFailure: connection unsuccessful
12-20 11:51:09.606 16769-16769/com.work.app D/MqttBridgeService: onFailure: connection unsuccessful
12-20 11:51:09.606 16769-16769/com.work.app W/System.err: Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /10.31.252.211 (port 1883) after 30000ms: isConnected failed: ECONNREFUSED (Connection refused)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule.start(TCPNetworkModule.java:79)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at org.eclipse.paho.client.mqttv3.internal.ClientComms$ConnectBG.run(ClientComms.java:590)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at java.lang.Thread.run(Thread.java:818)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err: Caused by: java.net.ConnectException: failed to connect to /10.31.252.211 (port 1883) after 30000ms: isConnected failed: ECONNREFUSED (Connection refused)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at libcore.io.IoBridge.isConnected(IoBridge.java:234)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at libcore.io.IoBridge.connectErrno(IoBridge.java:171)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at libcore.io.IoBridge.connect(IoBridge.java:122)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:183)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:452)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at java.net.Socket.connect(Socket.java:884)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule.start(TCPNetworkModule.java:70)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:   ... 2 more
12-20 11:51:09.606 16769-16769/com.work.app W/System.err: Caused by: android.system.ErrnoException: isConnected failed: ECONNREFUSED (Connection refused)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:     at libcore.io.IoBridge.isConnected(IoBridge.java:223)
12-20 11:51:09.606 16769-16769/com.work.app W/System.err:   ... 8 more
12-20 11:51:09.606 16769-16769/com.work.app E/AndroidRuntime: FATAL EXCEPTION: main
                                                                     Process: com.work.app, PID: 16769
                                                                     Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /10.31.252.211 (port 1883) after 30000ms:

问题

为什么这段代码会抛出一个崩溃应用程序的异常？理想情况下，它应该处理异常？我在这里错过了什么？
为什么不重试3次？
如果我从e.onError(throwable)方法同步拨打Flowable.subscribe()，为什么相同的代码会重试？

参考

Answer 1

由于您subscribe使用Consumer<String>，因此您没有为流定义错误处理程序。这意味着错误将通过RxJavaPlugins.getErrorHandler().handleError(...)传递给默认错误处理程序。在Android上，这个处理程序似乎会导致致命的错误。要解决此问题，请使用Observer<String>代替Consumer<String>
日志似乎表明客户端失败3次（“onFailure”被提及三次）在Rx之外做任何事情。如果我不得不猜测客户端可能是有状态的，这意味着在初始连接后跟随调用client.connect(...)会出现某种形式的奇怪行为导致问题。由于日志显示error - 1 sec wait - error, error，我猜回调仍然有效，因此第二次失败会被发送到RxJava两次。
假设你在谈论同步时谈论waitForCompletion()方法，它将支持我在2中的假设。由于没有注册回调，每个throwable只会报告一次，修复行为。

我不确定为什么发射器在终止后会保持功能（onError / onComplete），但由于规范要求这些方法只调用一次，因此可能是未指定的行为导致此问题。

Answer 2

我终于有了这个工作！

事实证明，这不是RxJava2的问题，而是Mqtt（Eclipse Paho）在主线程上运行回调

package com.alphavoice.sampleproject.community.user;

import org.json.JSONObject;

public class User {
    public User(JSONObject dataset) {

    }
}

的方式，即使客户端是在不同的线程上创建的！

对此的简单解决方案是等待客户端在其创建的线程上进行连接。除了这个方法
之外，问题中共享的代码是正确的
package com.alphavoice.sampleproject.community.user; import org.json.JSONObject; public class User { public User(JSONObject dataset) { } }

希望这可以帮助那些使用这些库的人：）

RxJava2：无法使用retryWhen处理异步回调异常

2 个答案: