It is a well known fact Spring Webflux applications should not be blocking applications.
Was just wondering, is the app considered as blocking application, if there is a blocking call on start up, but no blocking call on business logic? Just a general question.
I have an example, (super easy to reproduce) where I am using Blockhound in order to test if the app is blocking. While instantiating Bloudhound in my unit and integration tests, the flow has been proven non blocking (very happy).
However, with a Blockhound instantiated on start up, Spring Webflux + Reactive Cassandra like this:
package com.webflux.question.blockingg;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import reactor.blockhound.BlockHound;
@SpringBootApplication
public class Application {
static {
BlockHound.install();
}
public static void main(String[] args) {
SpringApplication.run(Application.class);
}
}
(the Cassandra parts)
package com.webflux.question.blockingg.configuration;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.cassandra.config.AbstractReactiveCassandraConfiguration;
import org.springframework.data.cassandra.config.CqlSessionFactoryBean;
import org.springframework.data.cassandra.repository.config.EnableReactiveCassandraRepositories;
import org.springframework.lang.NonNull;
@Configuration
@EnableReactiveCassandraRepositories
public class CassandraConfiguration extends AbstractReactiveCassandraConfiguration {
@Value("${spring.data.cassandra.username}")
private String username;
@Value("${spring.data.cassandra.password}")
private String passPhrase;
@Value("${spring.data.cassandra.keyspace-name}")
private String keyspace;
@Value("${spring.data.cassandra.datacenter}")
private String datacenter;
@Value("${spring.data.cassandra.contact-points}")
private String contactPoints;
@Value("${spring.data.cassandra.port}")
private int port;
@Bean
@NonNull
@Override
public CqlSessionFactoryBean cassandraSession() {
final CqlSessionFactoryBean cqlSessionFactoryBean = new CqlSessionFactoryBean();
cqlSessionFactoryBean.setContactPoints(contactPoints);
cqlSessionFactoryBean.setKeyspaceName(keyspace);
cqlSessionFactoryBean.setLocalDatacenter(datacenter);
cqlSessionFactoryBean.setPort(port);
cqlSessionFactoryBean.setUsername(username);
cqlSessionFactoryBean.setPassword(passPhrase);
return cqlSessionFactoryBean;
}
@NonNull
@Override
protected String getKeyspaceName() {
return keyspace;
}
@Override
protected String getLocalDataCenter() {
return datacenter;
}
@NonNull
@Override
protected String getContactPoints() {
return contactPoints;
}
@Override
protected int getPort() {
return port;
}
}
The pom:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://maven.apache.org/POM/4.0.0"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.3.3.RELEASE</version>
<relativePath/>
</parent>
<groupId>com.webflux.question</groupId>
<artifactId>blocking</artifactId>
<version>0.2</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>11</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-cassandra-reactive</artifactId>
</dependency>
<dependency>
<groupId>io.projectreactor.tools</groupId>
<artifactId>blockhound</artifactId>
<version>1.0.4.RELEASE</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>11</source>
<target>11</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
I am seeing below on start up.
Does it means my app is blocking?
Will the event loop be hurt because of this?
Is there a way to workaround this?
Thank you for your time.
Caused by: java.lang.IllegalArgumentException: Error instantiating class AtomicTimestampGenerator (specified by advanced.timestamp-generator.class): Blocking call! java.io.FileOutputStream#writeBytes
at com.datastax.oss.driver.internal.core.util.Reflection.buildFromConfig(Reflection.java:239)
at com.datastax.oss.driver.internal.core.util.Reflection.buildFromConfig(Reflection.java:94)
at com.datastax.oss.driver.internal.core.context.DefaultDriverContext.buildTimestampGenerator(DefaultDriverContext.java:368)
at com.datastax.oss.driver.internal.core.util.concurrent.LazyReference.get(LazyReference.java:55)
at com.datastax.oss.driver.internal.core.context.DefaultDriverContext.getTimestampGenerator(DefaultDriverContext.java:743)
at com.datastax.oss.driver.internal.core.session.DefaultSession$SingleThreaded.init(DefaultSession.java:349)
at com.datastax.oss.driver.internal.core.session.DefaultSession$SingleThreaded.access$1100(DefaultSession.java:300)
at com.datastax.oss.driver.internal.core.session.DefaultSession.lambda$init$0(DefaultSession.java:146)
at io.netty.util.concurrent.PromiseTask.runTask(PromiseTask.java:98)
at io.netty.util.concurrent.PromiseTask.run(PromiseTask.java:106)
at io.netty.channel.DefaultEventLoop.run(DefaultEventLoop.java:54)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: reactor.blockhound.BlockingOperationError: Blocking call! java.io.FileOutputStream#writeBytes
at java.base/java.io.FileOutputStream.writeBytes(FileOutputStream.java)
at java.base/java.io.FileOutputStream.write(FileOutputStream.java:354)
at org.apache.logging.log4j.core.appender.OutputStreamManager.writeToDestination(OutputStreamManager.java:250)
at org.apache.logging.log4j.core.appender.FileManager.writeToDestination(FileManager.java:273)
at org.apache.logging.log4j.core.appender.rolling.RollingFileManager.writeToDestination(RollingFileManager.java:240)
at org.apache.logging.log4j.core.appender.OutputStreamManager.flushBuffer(OutputStreamManager.java:282)
at org.apache.logging.log4j.core.appender.OutputStreamManager.flush(OutputStreamManager.java:291)
at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.directEncodeEvent(AbstractOutputStreamAppender.java:199)
at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.tryAppend(AbstractOutputStreamAppender.java:190)
at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.append(AbstractOutputStreamAppender.java:181)
at org.apache.logging.log4j.core.appender.RollingFileAppender.append(RollingFileAppender.java:312)
at org.apache.logging.log4j.core.config.AppenderControl.tryCallAppender(AppenderControl.java:156)
at org.apache.logging.log4j.core.config.AppenderControl.callAppender0(AppenderControl.java:129)
at org.apache.logging.log4j.core.config.AppenderControl.callAppenderPreventRecursion(AppenderControl.java:120)
at org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:84)
at org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:543)
at org.apache.logging.log4j.core.config.LoggerConfig.processLogEvent(LoggerConfig.java:502)
at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:485)
at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:460)
at org.apache.logging.log4j.core.config.AwaitCompletionReliabilityStrategy.log(AwaitCompletionReliabilityStrategy.java:82)
at org.apache.logging.log4j.core.Logger.log(Logger.java:161)
at org.apache.logging.log4j.spi.AbstractLogger.tryLogMessage(AbstractLogger.java:2198)
at org.apache.logging.log4j.spi.AbstractLogger.logMessageTrackRecursion(AbstractLogger.java:2152)
at org.apache.logging.log4j.spi.AbstractLogger.logMessageSafely(AbstractLogger.java:2135)
at org.apache.logging.log4j.spi.AbstractLogger.logMessage(AbstractLogger.java:2016)
at org.apache.logging.log4j.spi.AbstractLogger.logIfEnabled(AbstractLogger.java:1875)
at org.apache.logging.slf4j.Log4jLogger.info(Log4jLogger.java:179)
at com.datastax.oss.driver.internal.core.time.Clock.getInstance(Clock.java:35)
at com.datastax.oss.driver.internal.core.time.MonotonicTimestampGenerator.buildClock(MonotonicTimestampGenerator.java:109)
at com.datastax.oss.driver.internal.core.time.MonotonicTimestampGenerator.<init>(MonotonicTimestampGenerator.java:43)
at com.datastax.oss.driver.internal.core.time.AtomicTimestampGenerator.<init>(AtomicTimestampGenerator.java:52)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
at com.datastax.oss.driver.internal.core.util.Reflection.buildFromConfig(Reflection.java:232)
... 14 more
Official response from Datastax team:
The error is happening when Spring is building the application context, which happens when the application starts. Blocking calls are usually allowed during this phase, even for reactive / non-blocking applications – otherwise, your application would be totally unable to read a config file, for instance – since this is a blocking call.
Actively working on JAVA-2449 right now. I will change Uuids.random() to use non-blocking stuff.