为什么 Spring Webflux 只接受 256 个并行请求?

Question

在默认配置中，Spring Webflux似乎将并行请求的数量限制为256个。

我的设置有这个非常简单的控制器：

@RestController
public class SimpleRestController {
private final Log logger = LogFactory.getLog(getClass());
private AtomicLong countEnter = new AtomicLong(0);
private AtomicLong countExit = new AtomicLong(0);
@GetMapping(value = "/delayed")
public Mono<String> delayed() {
logger.info("delayed ENTER " + countEnter.incrementAndGet());
return Mono.just("result").delayElement(Duration.ofSeconds(60))
.doOnNext(s -> logger.info("delayed EXIT " + countExit.incrementAndGet()));
}
}

该配置仅启用 WebFlux：

@SpringBootConfiguration
@EnableWebFlux
public class SearchServiceConfiguration {
}

依赖关系只有少数：

<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>10</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
<configuration>
<source>10</source>
<target>10</target>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
</plugins>
</build>

我使用此脚本并行调用端点：

#!/usr/bin/env bash
for p in `seq 1 1000`;
do
curl -s http://localhost:8080/delayed &
done
wait
echo "All done"

对于第 257 个请求，返回Resource temporarily unavailable。

哪个设置会限制并行请求的数量？

这是生成的日志输出：

2018-10-26 14:27:27.253  INFO 23728 --- [           main] s.w.r.r.m.a.RequestMappingHandlerMapping : Mapped "{[/sleep],methods=[GET],produces=[application/stream+json]}" onto public java.lang.String controller.SimpleRestController.sleep() throws java.lang.InterruptedException
2018-10-26 14:27:27.253  INFO 23728 --- [           main] s.w.r.r.m.a.RequestMappingHandlerMapping : Mapped "{[/delayed],methods=[GET]}" onto public reactor.core.publisher.Mono<java.lang.String> controller.SimpleRestController.delayed()
2018-10-26 14:27:27.315  INFO 23728 --- [           main] o.s.w.r.r.m.a.ControllerMethodResolver   : Looking for @ControllerAdvice: org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext@3cdf2c61: startup date [Fri Oct 26 14:27:26 CEST 2018]; root of context hierarchy
2018-10-26 14:27:27.639  INFO 23728 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-10-26 14:27:27.938  INFO 23728 --- [ctor-http-nio-1] r.ipc.netty.tcp.BlockingNettyContext     : Started HttpServer on /0:0:0:0:0:0:0:0:8080
2018-10-26 14:27:27.939  INFO 23728 --- [           main] o.s.b.web.embedded.netty.NettyWebServer  : Netty started on port(s): 8080
2018-10-26 14:27:27.943  INFO 23728 --- [           main] d.h.s.s.SimpleApplication                : Started SimpleApplication in 1.548 seconds (JVM running for 2.396)
2018-10-26 14:27:34.295  INFO 23728 --- [ctor-http-nio-5] d.h.s.s.controller.SimpleRestController  : delayed ENTER 2
2018-10-26 14:27:34.295  INFO 23728 --- [ctor-http-nio-3] d.h.s.s.controller.SimpleRestController  : delayed ENTER 1
2018-10-26 14:27:34.295  INFO 23728 --- [ctor-http-nio-4] d.h.s.s.controller.SimpleRestController  : delayed ENTER 4
2018-10-26 14:27:34.295  INFO 23728 --- [ctor-http-nio-2] d.h.s.s.controller.SimpleRestController  : delayed ENTER 3
2018-10-26 14:27:34.324  INFO 23728 --- [ctor-http-nio-6] d.h.s.s.controller.SimpleRestController  : delayed ENTER 5
2018-10-26 14:27:34.351  INFO 23728 --- [ctor-http-nio-7] d.h.s.s.controller.SimpleRestController  : delayed ENTER 6
2018-10-26 14:27:34.381  INFO 23728 --- [ctor-http-nio-8] d.h.s.s.controller.SimpleRestController  : delayed ENTER 7
2018-10-26 14:27:34.413  INFO 23728 --- [ctor-http-nio-1] d.h.s.s.controller.SimpleRestController  : delayed ENTER 8
2018-10-26 14:27:34.438  INFO 23728 --- [ctor-http-nio-2] d.h.s.s.controller.SimpleRestController  : delayed ENTER 9
2018-10-26 14:27:34.466  INFO 23728 --- [ctor-http-nio-3] d.h.s.s.controller.SimpleRestController  : delayed ENTER 10
2018-10-26 14:27:34.497  INFO 23728 --- [ctor-http-nio-4] d.h.s.s.controller.SimpleRestController  : delayed ENTER 11
2018-10-26 14:27:34.526  INFO 23728 --- [ctor-http-nio-5] d.h.s.s.controller.SimpleRestController  : delayed ENTER 12
2018-10-26 14:27:34.561  INFO 23728 --- [ctor-http-nio-6] d.h.s.s.controller.SimpleRestController  : delayed ENTER 13
2018-10-26 14:27:34.594  INFO 23728 --- [ctor-http-nio-7] d.h.s.s.controller.SimpleRestController  : delayed ENTER 14
...
2018-10-26 14:27:42.675  INFO 23728 --- [ctor-http-nio-6] d.h.s.s.controller.SimpleRestController  : delayed ENTER 253
2018-10-26 14:27:42.711  INFO 23728 --- [ctor-http-nio-7] d.h.s.s.controller.SimpleRestController  : delayed ENTER 254
2018-10-26 14:27:42.745  INFO 23728 --- [ctor-http-nio-8] d.h.s.s.controller.SimpleRestController  : delayed ENTER 255
2018-10-26 14:27:42.774  INFO 23728 --- [ctor-http-nio-1] d.h.s.s.controller.SimpleRestController  : delayed ENTER 256
2018-10-26 14:28:04.312  INFO 23728 --- [     parallel-3] d.h.s.s.controller.SimpleRestController  : delayed EXIT 1
2018-10-26 14:28:04.312  INFO 23728 --- [     parallel-2] d.h.s.s.controller.SimpleRestController  : delayed EXIT 2
2018-10-26 14:28:04.321  INFO 23728 --- [     parallel-2] d.h.s.s.controller.SimpleRestController  : delayed EXIT 3
2018-10-26 14:28:04.321  INFO 23728 --- [     parallel-2] d.h.s.s.controller.SimpleRestController  : delayed EXIT 4
2018-10-26 14:28:04.333  INFO 23728 --- [     parallel-4] d.h.s.s.controller.SimpleRestController  : delayed EXIT 5
2018-10-26 14:28:04.359  INFO 23728 --- [     parallel-5] d.h.s.s.controller.SimpleRestController  : delayed EXIT 6
2018-10-26 14:28:04.389  INFO 23728 --- [     parallel-6] d.h.s.s.controller.SimpleRestController  : delayed EXIT 7
2018-10-26 14:28:04.421  INFO 23728 --- [     parallel-7] d.h.s.s.controller.SimpleRestController  : delayed EXIT 8
2018-10-26 14:28:04.446  INFO 23728 --- [     parallel-8] d.h.s.s.controller.SimpleRestController  : delayed EXIT 9
2018-10-26 14:28:04.474  INFO 23728 --- [     parallel-1] d.h.s.s.controller.SimpleRestController  : delayed EXIT 10
2018-10-26 14:28:04.505  INFO 23728 --- [     parallel-2] d.h.s.s.controller.SimpleRestController  : delayed EXIT 11
...
2018-10-26 14:28:12.570  INFO 23728 --- [     parallel-1] d.h.s.s.controller.SimpleRestController  : delayed EXIT 250
2018-10-26 14:28:12.607  INFO 23728 --- [     parallel-2] d.h.s.s.controller.SimpleRestController  : delayed EXIT 251
2018-10-26 14:28:12.643  INFO 23728 --- [     parallel-3] d.h.s.s.controller.SimpleRestController  : delayed EXIT 252
2018-10-26 14:28:12.683  INFO 23728 --- [     parallel-4] d.h.s.s.controller.SimpleRestController  : delayed EXIT 253
2018-10-26 14:28:12.719  INFO 23728 --- [     parallel-5] d.h.s.s.controller.SimpleRestController  : delayed EXIT 254
2018-10-26 14:28:12.752  INFO 23728 --- [     parallel-6] d.h.s.s.controller.SimpleRestController  : delayed EXIT 255
2018-10-26 14:28:12.782  INFO 23728 --- [     parallel-7] d.h.s.s.controller.SimpleRestController  : delayed EXIT 256

Answer 1

这不是我在本地设置中看到的。将控制器更改为以下内容会将"onNext 1"打印为"onNext 1000"：

AtomicLong count = new AtomicLong(0);
@GetMapping("/delayed")
public Mono<String> delayed() {
return Mono.just("result").delayElement(Duration.ofSeconds(30))
.doOnNext(s -> {
logger.info("onNext " + count.incrementAndGet());
});
}

在您的一条评论中，您提到了特定于 Servlet 的CommonsRequestLoggingFilter。这告诉我你运行的不是Spring WebFlux应用程序，而是Spring MVC应用程序。如果你运行的是 Spring Boot，并且类路径上有 Spring MVC，Spring Boot 会为你配置一个 Spring MVC 应用程序。

默认情况下，Spring MVC将使用SimpleAsyncTaskExecutor来调度这些请求的异步处理(Spring MVC 支持反应式返回类型，但会将它们视为@Async请求，异步但不是非阻塞(。我认为默认情况下SimpleAsyncTaskExecutor没有并发限制。也许您在应用程序中配置了一个任务执行器，将并发性限制为 256？

我尝试使用 Spring MVC 应用程序重现它，但仍然处理了 999 个请求，并在日志中解决了一个异常：

.w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.web.context.request.async.AsyncRequestTimeoutException]

Answer 2

服务器不是您的限制因素。该错误表示由于资源限制，创建后台进程失败。有几种可能的原因：

• 内存 - 每个进程都需要内存来加载 curl。
• 进程 - 可以创建的进程数可能有限制
• 打开文件 - 每个进程打开多个"文件"。这是用引号括起来的，因为"文件"包括网络连接和由curl加载的动态库。一次可以打开的数量有系统范围的限制。