Blockhound detects block call in DefaultConnectionFuture

[gustavosci]

Bug Report

While testing we detected a blocking call in lettuce client, specifically in the class DefaultConnectionFuture.
How could we avoid this block call?

Lettuce version: 6.0.1.RELEASE

Stack trace: at java.base/jdk.internal.misc.Unsafe.park(Unsafe.java) ~[na:na] at java.base/java.util.concurrent.locks.LockSupport.park(LockSupport.java:194) ~[na:na] at java.base/java.util.concurrent.CompletableFuture$Signaller.block(CompletableFuture.java:1796) ~[na:na] at java.base/java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3128) ~[na:na] at java.base/java.util.concurrent.CompletableFuture.waitingGet(CompletableFuture.java:1823) ~[na:na] at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1998) ~[na:na] at io.lettuce.core.DefaultConnectionFuture.get(DefaultConnectionFuture.java:69) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at io.lettuce.core.AbstractRedisClient.getConnection(AbstractRedisClient.java:315) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at io.lettuce.core.RedisClient.connect(RedisClient.java:211) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at org.springframework.data.redis.connection.lettuce.StandaloneConnectionProvider.lambda$getConnection$1(StandaloneConnectionProvider.java:115) ~[spring-data-redis-2.4.1.jar:2.4.1] at java.base/java.util.Optional.orElseGet(Optional.java:369) ~[na:na] at org.springframework.data.redis.connection.lettuce.StandaloneConnectionProvider.getConnection(StandaloneConnectionProvider.java:115) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$ExceptionTranslatingConnectionProvider.getConnection(LettuceConnectionFactory.java:1459) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$SharedConnection.getNativeConnection(LettuceConnectionFactory.java:1247) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$SharedConnection.getConnection(LettuceConnectionFactory.java:1230) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getSharedReactiveConnection(LettuceConnectionFactory.java:989) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getReactiveConnection(LettuceConnectionFactory.java:445) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getReactiveConnection(LettuceConnectionFactory.java:98) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.core.ReactiveRedisTemplate.lambda$doInConnection$0(ReactiveRedisTemplate.java:198) ~[spring-data-redis-2.4.1.jar:2.4.1]

Thanks in advance.

[mp911de]

That's a Spring Data Redis issue where you need to enable eager connection factory initialization.

[gustavosci]

Hey @mp911de, first of all, thanks for your answer.

I tried to use eager connection factory initialization, however now I'm getting the following error when trying to connect to redis during application startup:

Caused by: io.lettuce.core.RedisConnectionException: Unable to connect to localhost:6379 at io.lettuce.core.RedisConnectionException.create(RedisConnectionException.java:78) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at io.lettuce.core.RedisConnectionException.create(RedisConnectionException.java:56) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at io.lettuce.core.AbstractRedisClient.getConnection(AbstractRedisClient.java:320) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at io.lettuce.core.RedisClient.connect(RedisClient.java:211) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at org.springframework.data.redis.connection.lettuce.StandaloneConnectionProvider.lambda$getConnection$1(StandaloneConnectionProvider.java:115) ~[spring-data-redis-2.4.1.jar:2.4.1] at java.base/java.util.Optional.orElseGet(Optional.java:369) ~[na:na] at org.springframework.data.redis.connection.lettuce.StandaloneConnectionProvider.getConnection(StandaloneConnectionProvider.java:115) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$ExceptionTranslatingConnectionProvider.getConnection(LettuceConnectionFactory.java:1459) ~[spring-data-redis-2.4.1.jar:2.4.1] ... 66 common frames omitted Caused by: io.netty.channel.StacklessClosedChannelException: null at io.netty.channel.AbstractChannel$AbstractUnsafe.ensureOpen(ChannelPromise)(Unknown Source) ~[netty-transport-4.1.54.Final.jar:4.1.54.Final]

After getting this, I also tried to change the related beans (ReactiveRedisConnectionFactory and ReactiveRedisTemplate) to be lazy, since my assumption is that at application startup the netty channels are not ready to be used yet. Well, the application started, but when I made the first operation with redis and the bean LettuceConnectionFactory was created, I got the same block call:

Caused by: reactor.blockhound.BlockingOperationError: Blocking call! jdk.internal.misc.Unsafe#park at java.base/jdk.internal.misc.Unsafe.park(Unsafe.java) ~[na:na] at java.base/java.util.concurrent.locks.LockSupport.park(LockSupport.java:194) ~[na:na] at java.base/java.util.concurrent.CompletableFuture$Signaller.block(CompletableFuture.java:1796) ~[na:na] at java.base/java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3128) ~[na:na] at java.base/java.util.concurrent.CompletableFuture.waitingGet(CompletableFuture.java:1823) ~[na:na] at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1998) ~[na:na] at io.lettuce.core.DefaultConnectionFuture.get(DefaultConnectionFuture.java:69) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at io.lettuce.core.AbstractRedisClient.getConnection(AbstractRedisClient.java:315) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at io.lettuce.core.RedisClient.connect(RedisClient.java:211) ~[lettuce-core-6.0.1.RELEASE.jar:6.0.1.RELEASE] at org.springframework.data.redis.connection.lettuce.StandaloneConnectionProvider.lambda$getConnection$1(StandaloneConnectionProvider.java:115) ~[spring-data-redis-2.4.1.jar:2.4.1] at java.base/java.util.Optional.orElseGet(Optional.java:369) ~[na:na] at org.springframework.data.redis.connection.lettuce.StandaloneConnectionProvider.getConnection(StandaloneConnectionProvider.java:115) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$ExceptionTranslatingConnectionProvider.getConnection(LettuceConnectionFactory.java:1459) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$SharedConnection.getNativeConnection(LettuceConnectionFactory.java:1247) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory$SharedConnection.getConnection(LettuceConnectionFactory.java:1230) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.getSharedConnection(LettuceConnectionFactory.java:979) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.initConnection(LettuceConnectionFactory.java:475) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory.afterPropertiesSet(LettuceConnectionFactory.java:297) ~[spring-data-redis-2.4.1.jar:2.4.1] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1847) ~[spring-beans-5.3.1.jar:5.3.1] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1784) ~[spring-beans-5.3.1.jar:5.3.1] ... 142 common frames omitted

My current simple config is:

    @Bean
    @Primary
    fun getReactiveRedisConnectionFactory() : ReactiveRedisConnectionFactory {
        val factory = LettuceConnectionFactory()
        factory.eagerInitialization = true
        return factory
    }

    @Bean
    fun getReactiveRedisTemplate(factory: ReactiveRedisConnectionFactory): ReactiveRedisTemplate<String, Order> {
        val keySerializer = StringRedisSerializer()
        val valueSerializer = Jackson2JsonRedisSerializer(Order::class.java)

        val builder = RedisSerializationContext.newSerializationContext<String, Order>(keySerializer)
        val context = builder.value(valueSerializer).build()

        return ReactiveRedisTemplate(factory, context)
    }

Am I missing something important here?

Thanks for your help!

[mp911de]

That is the natural consequence. Either you can initialize the connection at startup and move blocking calls onto the main thread or lazy initialization on the first access where blocking calls happen on the thread that requests the connection.