Ignite memory leaks in 2.8.0

[Andrey Davydov]

Hello,   There are at least two way link to IgniteKernal leaks to GC root and makes it unavailable for GC.   The first one:   this     - value: org.apache.ignite.internal.IgniteKernal #1 <- grid     - class: org.apache.ignite.internal.GridKernalContextImpl, value: org.apache.ignite.internal.IgniteKernal #1   <- ctx     - class: org.apache.ignite.internal.processors.query.h2.IgniteH2Indexing, value: org.apache.ignite.internal.GridKernalContextImpl #2    <- this$0     - class: org.apache.ignite.internal.processors.query.h2.IgniteH2Indexing$10, value: org.apache.ignite.internal.processors.query.h2.IgniteH2Indexing #2     <- serializer     - class: org.h2.util.JdbcUtils, value: org.apache.ignite.internal.processors.query.h2.IgniteH2Indexing$10 #1      <- [5395]     - class: java.lang.Object[], value: org.h2.util.JdbcUtils class JdbcUtils       <- elementData     - class: java.util.Vector, value: java.lang.Object[] #37309        <- classes     - class: sun.misc.Launcher$AppClassLoader, value: java.util.Vector #31         <- contextClassLoader (thread object)     - class: java.lang.Thread, value: sun.misc.Launcher$AppClassLoader #1   org.h2.util.JdbcUtils has static field JavaObjectSerializer serializer, which see IgniteKernal via IgniteH2Indexing. It make closed and stopped IgniteKernal non collectable by GC. If some Ignites run in same JVM, JdbcUtils will always use only one, and it can cause some races.   The second way:   this     - value: org.apache.ignite.internal.IgniteKernal #2 <- grid     - class: org.apache.ignite.internal.GridKernalContextImpl, value: org.apache.ignite.internal.IgniteKernal #2   <- ctx     - class: org.apache.ignite.internal.processors.cache.GridCacheContext, value: org.apache.ignite.internal.GridKernalContextImpl #1    <- cctx     - class: org.apache.ignite.internal.processors.cache.distributed.dht.GridDhtCacheEntry, value: org.apache.ignite.internal.processors.cache.GridCacheContext #24     <- parent     - class: org.apache.ignite.internal.processors.cache.GridCacheMvccCandidate, value: org.apache.ignite.internal.processors.cache.distributed.dht.GridDhtCacheEntry #4      <- [0]     - class: java.lang.Object[], value: org.apache.ignite.internal.processors.cache.GridCacheMvccCandidate #1       <- elements     - class: java.util.ArrayDeque, value: java.lang.Object[] #43259        <- value     - class: java.lang.ThreadLocal$ThreadLocalMap$Entry, value: java.util.ArrayDeque #816         <- [119]     - class: java.lang.ThreadLocal$ThreadLocalMap$Entry[], value: java.lang.ThreadLocal$ThreadLocalMap$Entry #51          <- table     - class: java.lang.ThreadLocal$ThreadLocalMap, value: java.lang.ThreadLocal$ThreadLocalMap$Entry[] #21           <- threadLocals (thread object)     - class: java.lang.Thread, value: java.lang.ThreadLocal$ThreadLocalMap #2   Link to IgniteKernal leaks to ThreadLocal variable, so when we start/stop many instances of Ignite in same jvm during testing, we got many stopped “zomby” ignites on ThreadLocal context of main test thread and it cause OutOfMemory after some dozens of tests.   Andrey.