Question

rxjava2版本2.1.5

尝试理解RxJava2对observable的多个订阅。有一个简单的文件监视服务，跟踪创建，修改，删除目录中的文件。我添加了2个订阅者，并期望在两个订阅者上打印事件。当我将文件复制到监视目录时，我看到一个订阅者打印出该事件。然后，当我删除文件时，我看到第二个订阅者打印出事件。我期待两个订阅者都打印事件。我在这里缺少什么？

import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;

import java.io.IOException;
import java.nio.file.FileSystem;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.concurrent.TimeUnit;

import io.reactivex.BackpressureStrategy;
import io.reactivex.Flowable;
import io.reactivex.schedulers.Schedulers;

public class MyRxJava2DirWatcher {

    public Flowable<WatchEvent<?>> createFlowable(WatchService watcher, Path path) {

        return Flowable.create(subscriber -> {

            boolean error = false;
            WatchKey key;
            try {

                key = path.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
            }
            catch (IOException e) {
                subscriber.onError(e);
                error = true;
            }

            while (!error) {
                key = watcher.take();

                for (final WatchEvent<?> event : key.pollEvents()) {
                    subscriber.onNext(event);
                }

                key.reset();
            }

        }, BackpressureStrategy.BUFFER);

    }

    public static void main(String[] args) throws IOException, InterruptedException {
        Path path = Paths.get("c:\\temp\\delete");
        final FileSystem fileSystem = path.getFileSystem();
        WatchService watcher = fileSystem.newWatchService();

        MyRxJava2DirWatcher my = new MyRxJava2DirWatcher();
        my.createFlowable(watcher, path).subscribeOn(Schedulers.computation()).subscribe(event -> {
            System.out.println("1>>Event kind:" + event.kind() + ". File affected: " + event.context() + ". "
                    + Thread.currentThread().getName());

        }, onError -> {
            System.out.println("1>>" + Thread.currentThread().getName());
            onError.printStackTrace();
        });

        // MyRxJava2DirWatcher my2 = new MyRxJava2DirWatcher();

        my.createFlowable(watcher, path).subscribeOn(Schedulers.computation()).subscribe(event -> {
            System.out.println("2>>Event kind:" + event.kind() + ". File affected: " + event.context() + ". "
                    + Thread.currentThread().getName());

        }, onError -> {
            System.out.println("2>>" + Thread.currentThread().getName());
            onError.printStackTrace();
        });

        TimeUnit.MINUTES.sleep(1000);

    }
}

输出如下所示

2>>Event kind:ENTRY_CREATE. File affected: 1.txt. RxCachedThreadScheduler-2
2>>Event kind:ENTRY_MODIFY. File affected: 1.txt. RxCachedThreadScheduler-2
1>>Event kind:ENTRY_DELETE. File affected: 1.txt. RxCachedThreadScheduler-1

Answer 1

您会在两个WatchService之间共享相同的Flowable，并在其中竞争事件。如果您传入FileSystem而是在newWatchService()中致电Flowable.create，则应该收到所有事件Subscriber的次数：

public Flowable<WatchEvent<?>> createFlowable(FileSystem fs, Path path) {

    return Flowable.create(subscriber -> {

        WatchService watcher = fs.newWatchService();

        subscriber.setCancellable(() -> watcher.close());

        boolean error = false;
        WatchKey key;
        try {

            key = path.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
        }
        catch (IOException e) {
            subscriber.onError(e);
            error = true;
        }

        while (!error) {
            key = watcher.take();

            for (final WatchEvent<?> event : key.pollEvents()) {
                subscriber.onNext(event);
            }

            key.reset();
        }

    }, BackpressureStrategy.BUFFER);

}

另请注意，您应该使用subscribeOn(Schedulers.computation(), false)来避免poll与Subscriber一起陷入僵局。

Answer 2

您正在为两个不同的订阅者创建两个不同的Flowable。是否有一个Flowable订阅了两次，如下所示。

public static void main(String[] args) throws IOException, InterruptedException {
        Path path = Paths.get("c:\\temp\\delete");
        final FileSystem fileSystem = path.getFileSystem();
        WatchService watcher = fileSystem.newWatchService();

        MyRxJava2DirWatcher my = new MyRxJava2DirWatcher();
        Flowable myFlowable = my.createFlowable(watcher, path);

        myFlowable.subscribeOn(Schedulers.computation()).subscribe(event -> {
            System.out.println("1>>Event kind:" + event.kind() + ". File affected: " + event.context() + ". "
                    + Thread.currentThread().getName());

        }, onError -> {
            System.out.println("1>>" + Thread.currentThread().getName());
            onError.printStackTrace();
        });

        myFlowable.subscribeOn(Schedulers.computation()).subscribe(event -> {
            System.out.println("2>>Event kind:" + event.kind() + ". File affected: " + event.context() + ". "
                    + Thread.currentThread().getName());

        }, onError -> {
            System.out.println("2>>" + Thread.currentThread().getName());
            onError.printStackTrace();
        });

        TimeUnit.MINUTES.sleep(1000);

    }
}

RxJava2，Observable / Flowable的2个订阅者，但在任何一个上调用onNext

2 个答案: