Question

我正在尝试使用vertx executeBlocking来模拟我在

之后所做的实时场景

vertx.setPeriodic(1000, id ->{
    counter += 1;
    LOGGER.info("invoked method {} ",counter);
    vertx.executeBlocking(future -> {
        int counterFinal = counter;
        String result = service.blockingMethod("cycle "+counterFinal+" executed");
        future.complete(result);
    }, res -> {
        LOGGER.info(String.format("The result is: %s", res.result()));
    });

阻止方法非常简单

public String blockingMethod(String result){
    block(2);
    return result;
}

这就是结果

07:50:27.742 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - invoked method 1 
07:50:28.742 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - invoked method 2 
07:50:29.740 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - invoked method 3 
07:50:29.764 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - The result is: cycle 1 executed
07:50:30.739 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - invoked method 4 
07:50:31.739 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - invoked method 5 
07:50:31.773 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - The result is: cycle 3 executed
07:50:32.751 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - invoked method 6 
07:50:33.748 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - invoked method 7 
07:50:33.789 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.AsyncExperimentalVerticle - The result is: cycle 5 executed

它显然平均缺少两个事件，因为延迟设置为2秒。然后我将阻塞方法包装在一个类中，然后以下面的方式执行

vertx.setPeriodic(1000, id ->{
    counter++;
    LOGGER.info("invoked method {} ",counter);
    service.wrapperMethod("Hello", counter, new Handler<AsyncClass>() {
        @Override
        public void handle(AsyncClass event) {
            vertx.executeBlocking(future -> {
                String result = event.result();
                future.complete(result);
            }, res -> {
                LOGGER.info(String.format("The result is: %s", res.result()));
            });
        }
    });
});

并且以这种方式设计了包装器方法

public void wrapperMethod(String input, int cycle, Handler<AsyncClass> execute) {
    AsyncClass instance = new AsyncClass(input,String.valueOf(cycle)); // my custom class where the result method has a 2 sec delay
    execute.handle(instance);
}

然后我得到了预期的结果。

08:08:27.358 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - invoked method 1 
08:08:27.368 [vert.x-worker-thread-0] INFO lab.async.base.support.AsyncClass - Invoking method inside AsyncClass class
08:08:28.338 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - invoked method 2 
08:08:29.345 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - invoked method 3 
08:08:29.384 [vert.x-worker-thread-0] INFO lab.async.base.support.AsyncClass - Invoking method inside AsyncClass class
08:08:29.386 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - The result is: Hello world of cycle 1
08:08:30.347 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - invoked method 4 
08:08:31.351 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - invoked method 5 
08:08:31.391 [vert.x-worker-thread-0] INFO lab.async.base.support.AsyncClass - Invoking method inside AsyncClass class
08:08:31.391 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - The result is: Hello world of cycle 2
08:08:32.341 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - invoked method 6 
08:08:33.343 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - invoked method 7 
08:08:33.396 [vert.x-worker-thread-0] INFO lab.async.base.support.AsyncClass - Invoking method inside AsyncClass class
08:08:33.397 [vert.x-eventloop-thread-0] INFO lab.async.base.verticle.TestVerticle2 - The result is: Hello world of cycle 3

现在我看到异步执行而不会错过任何一个事件。我无法找到可能的解释。即使在包装方法中，如果我延迟n秒，它也会按预期错过事件。

有人请帮助我理解这种行为。

UPDATE1：

对于第二种情况，AsyncClass的结构在下面给出

public class AsyncClass {

    private static final Logger LOGGER = LoggerFactory.getLogger(AsyncClass.class);

    private String input;
    private String cycle;

    public AsyncClass(String input, String cycle) {
        this.input = input;
        this.cycle = cycle;
    }

    public String result(){
        LOGGER.info("Invoking method inside AsyncClass class");
        block(2);
        return input+" world of cycle "+cycle;
    }

    private void block(int pauseLimitInSecond){
        try {
            TimeUnit.SECONDS.sleep(pauseLimitInSecond);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            LOGGER.error("exception - > ", e);
        }
    }
}

Answer 1

您使用的executeBlocking method可确保按顺序执行阻止任务（一个接一个）。

因此，当执行第二个阻塞任务时（两秒钟后），counter变量已经增加了两次。因此1，3，5系列。

在使用包装类的其他尝试中，在调用counter之前捕获executeBlocking变量值。因此，当执行阻塞任务时，您将获得所期望的值。

Answer 2

观察到的行为归因于Lambda body variable capture，其中捕获了外部类引用（this）。

外部类实例变量counter将在评估 Lambda body 表达式时更改其值（在初始值上增加1），这会产生错觉意外行为。

保持相同的程序序列，您可以用Handler<Future<String>>实现替换 Lambda表达式体，其中counter外部实例变量存储在另一个实例变量中在处理程序执行体中使用：

private static final class BlockingHandler implements Handler<Future<String>> {

    private final YourBlockingService service;

    private final int counter;

    public BlockingHandler(int counter, YourBlockingService service) {
        this.counter = counter;
        this.service = service;
    }

    @Override
    public void handle(Future<String> event) {
        String result = service.blockingMethod("cycle " + this.counter + " executed", 2);
        event.complete(result);
    }
}

您的Verticle代码将如下所示：

this.vertx.setPeriodic(
      1000,
      id -> {
          counter += 1;
          LOGGER.info("invoked method {}", counter);
          vertx.executeBlocking(
                new YourBlockingHandler(this.counter, this.service),
                res -> LOGGER.info(String.format("The result is: %s", res.result()))
          );
      }
);

要恢复，上述行为仅与闭包语义有关，与 Vert.x 内部结构无关。

vertx executeBlocking不同的行为

2 个答案: