AsyncHttp4sServlet is not async

Bootstrap.scala

package net.shrine.api


import cats.effect.{ConcurrentEffect, IO}
import javax.servlet.annotation.WebListener
import javax.servlet.{ServletContextEvent, ServletContextListener}
import net.shrine.api.http4s.servlet.syntax.ShrineServletContextSyntax
import org.http4s.HttpRoutes
import org.http4s.dsl.impl.{->, /}
import org.http4s.dsl.io.{GET, Ok, Root, http4sOkSyntax}

import scala.concurrent.duration.DurationInt
import scala.language.higherKinds
import scala.concurrent.ExecutionContext.global

@WebListener
class Bootstrap extends ServletContextListener {

  override def contextInitialized(sce: ServletContextEvent): Unit = {
    val context = sce.getServletContext
    implicit val concurrentEffect: ConcurrentEffect[IO] = IO.ioConcurrentEffect(IO.contextShift(global))

    ShrineServletContextSyntax.mountService(
      context = context,
      name = "test http4s",
      service = service,
      asyncTimeout = 55.seconds
    )
  }

  override def contextDestroyed(sce: ServletContextEvent): Unit = {}

  val service: HttpRoutes[IO] = HttpRoutes.of[IO] {

    case _@GET -> Root / "ping" => Ok("pong")

    case _@GET -> Root / "parallel" =>
      val startTime = System.currentTimeMillis()
      scala.concurrent.blocking { Thread.sleep(15000) }
      val endTime = System.currentTimeMillis()

      val reply = s"blockingTestReq done in ${endTime - startTime}"

      Ok(reply)
  }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>shrine-base</artifactId>
        <groupId>net.shrine</groupId>
        <version>1.26.2.1-SNAPSHOT</version>
        <relativePath>../../pom.xml</relativePath>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>test-app</artifactId>
    <name>test http4s App</name>
    <packaging>jar</packaging>

    <build>
        <plugins>
            <plugin>
                <groupId>net.alchim31.maven</groupId>
                <artifactId>scala-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <dependency>
            <groupId>org.http4s</groupId>
            <artifactId>http4s-dsl_${scala-major-version}</artifactId>
            <version>0.19.0-M2</version>
        </dependency>
        <dependency>
            <groupId>org.http4s</groupId>
            <artifactId>http4s-core_${scala-major-version}</artifactId>
            <version>0.19.0-M2</version>
        </dependency>
        <dependency>
            <groupId>org.http4s</groupId>
            <artifactId>http4s-server_${scala-major-version}</artifactId>
            <version>0.19.0-M2</version>
        </dependency>
        <dependency>
            <groupId>org.http4s</groupId>
            <artifactId>http4s-servlet_${scala-major-version}</artifactId>
            <version>0.19.0-M2</version>
        </dependency>
        <dependency>
            <groupId>org.http4s</groupId>
            <artifactId>http4s-circe_${scala-major-version}</artifactId>
            <version>0.19.0-M2</version>
        </dependency>
        <dependency>
            <groupId>org.http4s</groupId>
            <artifactId>http4s-client_${scala-major-version}</artifactId>
            <version>0.19.0-M2</version>
        </dependency>
        <dependency>
            <groupId>org.http4s</groupId>
            <artifactId>http4s-testing_${scala-major-version}</artifactId>
            <version>0.19.0-M2</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>${slf4j-version}</version>
        </dependency>
    </dependencies>
</project>

ShrineServletContextSyntax.scala

package net.shrine.api.http4s.servlet.syntax

import cats.effect.{ConcurrentEffect, Effect}
import javax.servlet.{ServletContext, ServletRegistration}
import org.http4s.HttpRoutes
import org.http4s.server.DefaultServiceErrorHandler
import org.http4s.servlet.{AsyncHttp4sServlet, NonBlockingServletIo}

import scala.concurrent.duration.FiniteDuration
import scala.language.higherKinds

object ShrineServletContextSyntax {
  /* This mountService function is a copy of the mountService function in org.http4s.servlet.syntax.ServletContextSyntax.scala
     *  version 0.18.9 of http4s with the asyncTimeout added as parameter so that the default timeout of 30 seconds can be modified
     *  There is a bug filed at https://github.com/http4s/http4s/issues/1812
     */
  def mountService[F[_]: Effect](
                                  context : ServletContext,
                                  name: String,
                                  service: HttpRoutes[F],
                                  asyncTimeout: FiniteDuration,
                                  mapping: String = "/*")(
                                  implicit concurrentEffect: ConcurrentEffect[F]
  ): ServletRegistration.Dynamic = {
    //todo this won't work because by default the service is BlockingIO    val servlet = AsyncHttp4sServlet(service,asyncTimeout)

    val servlet = new AsyncHttp4sServlet(
      service = service,
      asyncTimeout = asyncTimeout,
      servletIo = NonBlockingServletIo(4096),
      serviceErrorHandler = DefaultServiceErrorHandler[F]
    )

    val reg = context.addServlet(name, servlet)
    reg.setLoadOnStartup(1)
    reg.setAsyncSupported(true)
    reg.addMapping(mapping)
    reg
  }
}

war pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>shrine-base</artifactId>
        <groupId>net.shrine</groupId>
        <version>1.26.2.1-SNAPSHOT</version>
        <relativePath>/../../pom.xml</relativePath>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>test-war</artifactId>
    <name>test http4s War</name>
    <packaging>war</packaging>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <configuration>
                    <warName>test</warName>
                </configuration>
            </plugin>
        </plugins>
    </build>
    <dependencies>
        <dependency>
            <groupId>net.shrine</groupId>
            <artifactId>test-app</artifactId>
            <version>${project.version}</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>${slf4j-version}</version>
            <scope>runtime</scope>
        </dependency>
    </dependencies>
</project>

web.xml

<?xml version="1.0"?>

<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_4.dtd">

<web-app>
    <listener>
        <listener-class>net.shrine.api.Bootstrap</listener-class>
    </listener>
</web-app>