vertx executeBlocking 不同的行为

Question

我正在试验 vertx executeBlocking，以模拟我遵循的实时场景

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()));
    });

阻塞方法非常简单

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

很明显平均漏掉了两个事件，因为延迟设置为2秒。然后我将阻塞方法包装在 class 中，然后按以下方式执行

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()));
            });
        }
    });
});

wrapper Method就是这样设计的

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

现在我看到了异步执行，没有遗漏任何一个事件。我找不到可能的解释。即使在包装器方法中，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。

更新1：

对于第二种情况，AsyncClass 的结构如下

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 确保阻塞任务按顺序执行（一个接一个）。

所以当第二个阻塞任务执行时（两秒后），counter变量已经递增了两次。因此 1、3、5 系列。

在您使用包装 class 的另一次尝试中，counter 变量值在调用 executeBlocking 之前被捕获。所以当执行阻塞任务时，你得到了你期望的值。

Answer 2

观察到的行为是由于 Lambda body variable capture 捕获了外部 class 引用 (this)。

外部 class 实例变量 counter 将在计算 Lambda 主体 表达式时更改其值（增加 1超过初始值）这给人一种意外行为的错觉。

保持相同的程序顺序，您可以将 Lambda 表达式 主体替换为 Handler<Future<String>> 实现，其中 counter 外部实例变量存储在另一个将在处理程序执行体中使用的实例变量：

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()))
          );
      }
);

恢复，上述行为仅与闭包语义相关，与Vert.x内部无关。

vertx executeBlocking 不同的行为

vertx executeBlocking different behaviour

java

multithreading

asynchronous

vert.x