In Java 8 it is shown as none of the available 4 c

Question

I have a container running a Spring Boot microservice. I am using openjdk version "1.8.0_212" under OpenJDK Runtime Environment (IcedTea 3.12.0) (Alpine 8.212.04-r0) When I use -XX:+PrintFlagsFinal flag and print the JVM parameters I expected to see

-XX:+UseParallelGC as true

But to my surprise none of the 4 collectors (-XX:+UseSerialGC,-XX:+UseParallelGC,-XX:+UseConcMarkSweepGC,–XX:+UseG1GC) were active.

Shown below is my dockerfile:

FROM openjdk:8-jdk-alpine
ADD  ./demo-0.0.1-SNAPSHOT.jar /usr/src/factorial/
WORKDIR /usr/src/factorial
EXPOSE 8080
CMD java $JAVA_OPTIONS -jar demo-0.0.1-SNAPSHOT.jar

I'm running this using:

  docker run -d --rm --name factorialorialContainer --memory='512m' --cpus=2 -p 8080:8080 -e JAVA_OPTIONS="$(cat /Users/sulekahelmini/Documents/fyp/fyp_work/MLscripts/$3)" suleka96/factorial:latest

The flags_base.txt

-Xms512m -Xmx512m -XX:+PrintFlagsFinal -version

This is part of the output of -XX:+PrintFlagsFinal

     intx UnguardOnExecutionViolation               = 0                                   {product}
     bool UnlinkSymbolsALot                         = false                               {product}
     bool Use486InstrsOnly                          = false                               {ARCH product}
     bool UseAES                                    = true                                {product}
     bool UseAESIntrinsics                          = true                                {product}
     intx UseAVX                                    = 2                                   {ARCH product}
     bool UseAdaptiveGCBoundary                     = false                               {product}
     bool UseAdaptiveGenerationSizePolicyAtMajorCollection  = true                                {product}
     bool UseAdaptiveGenerationSizePolicyAtMinorCollection  = true                                {product}
     bool UseAdaptiveNUMAChunkSizing                = true                                {product}
     bool UseAdaptiveSizeDecayMajorGCCost           = true                                {product}
     bool UseAdaptiveSizePolicy                     = true                                {product}
     bool UseAdaptiveSizePolicyFootprintGoal        = true                                {product}
     bool UseAdaptiveSizePolicyWithSystemGC         = false                               {product}
     bool UseAddressNop                             = true                                {ARCH product}
     bool UseAltSigs                                = false                               {product}
     bool UseAutoGCSelectPolicy                     = false                               {product}
     bool UseBMI1Instructions                       = true                                {ARCH product}
     bool UseBMI2Instructions                       = true                                {ARCH product}
     bool UseBiasedLocking                          = true                                {product}
     bool UseBimorphicInlining                      = true                                {C2 product}
     bool UseBoundThreads                           = true                                {product}
     bool UseCLMUL                                  = true                                {ARCH product}
     bool UseCMSBestFit                             = true                                {product}
     bool UseCMSCollectionPassing                   = true                                {product}
     bool UseCMSCompactAtFullCollection             = true                                {product}
     bool UseCMSInitiatingOccupancyOnly             = false                               {product}
     bool UseCRC32Intrinsics                        = true                                {product}
     bool UseCodeCacheFlushing                      = true                                {product}
     bool UseCompiler                               = true                                {product}
     bool UseCompilerSafepoints                     = true                                {product}
     bool UseCompressedClassPointers               := true                                {lp64_product}
     bool UseCompressedOops                        := true                                {lp64_product}
     bool UseConcMarkSweepGC                        = false                               {product}
     bool UseCondCardMark                           = false                               {C2 product}
     bool UseContainerSupport                       = true                                {product}
     bool UseCountLeadingZerosInstruction           = true                                {ARCH product}
     bool UseCountTrailingZerosInstruction          = true                                {ARCH product}
     bool UseCountedLoopSafepoints                  = false                               {C2 product}
     bool UseCounterDecay                           = true                                {product}
     bool UseDivMod                                 = true                                {C2 product}
     bool UseDynamicNumberOfGCThreads               = false                               {product}
     bool UseFPUForSpilling                         = true                                {C2 product}
     bool UseFastAccessorMethods                    = false                               {product}
     bool UseFastEmptyMethods                       = false                               {product}
     bool UseFastJNIAccessors                       = true                                {product}
     bool UseFastStosb                              = true                                {ARCH product}
     bool UseG1GC                                   = false                               {product}
     bool UseGCLogFileRotation                      = false                               {product}
     bool UseGCOverheadLimit                        = true                                {product}
     bool UseGCTaskAffinity                         = false                               {product}
     bool UseHeavyMonitors                          = false                               {product}
     bool UseHugeTLBFS                              = false                               {product}
     bool UseInlineCaches                           = true                                {product}
     bool UseInterpreter                            = true                                {product}
     bool UseJumpTables                             = true                                {C2 product}
     bool UseLWPSynchronization                     = true                                {product}
     bool UseLargePages                             = false                               {pd product}
     bool UseLargePagesInMetaspace                  = false                               {product}
     bool UseLargePagesIndividualAllocation         = false                               {pd product}
     bool UseLinuxPosixThreadCPUClocks              = true                                {product}
     bool UseLockedTracing                          = false                               {product}
     bool UseLoopCounter                            = true                                {product}
     bool UseLoopInvariantCodeMotion                = true                                {C1 product}
     bool UseLoopPredicate                          = true                                {C2 product}
     bool UseMathExactIntrinsics                    = true                                {C2 product}
     bool UseMaximumCompactionOnSystemGC            = true                                {product}
     bool UseMembar                                 = false                               {pd product}
     bool UseMontgomeryMultiplyIntrinsic            = true                                {C2 product}
     bool UseMontgomerySquareIntrinsic              = true                                {C2 product}
     bool UseMulAddIntrinsic                        = true                                {C2 product}
     bool UseMultiplyToLenIntrinsic                 = true                                {C2 product}
     bool UseNUMA                                   = false                               {product}
     bool UseNUMAInterleaving                       = false                               {product}
     bool UseNewLongLShift                          = false                               {ARCH product}
     bool UseOSErrorReporting                       = false                               {pd product}
     bool UseOldInlining                            = true                                {C2 product}
     bool UseOnStackReplacement                     = true                                {pd product}
     bool UseOnlyInlinedBimorphic                   = true                                {C2 product}
     bool UseOprofile                               = false                               {product}
     bool UseOptoBiasInlining                       = true                                {C2 product}
     bool UsePSAdaptiveSurvivorSizePolicy           = true                                {product}
     bool UseParNewGC                               = false                               {product}
     bool UseParallelGC                             = false                               {product}
     bool UseParallelOldGC                          = false                               {product}
     bool UsePerfData                               = true                                {product}
     bool UsePopCountInstruction                    = true                                {product}
     bool UseRDPCForConstantTableBase               = false                               {C2 product}
     bool UseRTMDeopt                               = false                               {ARCH product}
     bool UseRTMLocking                             = false                               {ARCH product}
     bool UseSHA                                    = false                               {product}
     bool UseSHA1Intrinsics                         = false                               {product}
     bool UseSHA256Intrinsics                       = false                               {product}
     bool UseSHA512Intrinsics                       = false                               {product}
     bool UseSHM                                    = false                               {product}
     intx UseSSE                                    = 4                                   {product}
     bool UseSSE42Intrinsics                        = true                                {product}
     bool UseSerialGC                               = false                               {product}
     bool UseSharedSpaces                           = false                               {product}
     bool UseSignalChaining                         = true                                {product}
     bool UseSquareToLenIntrinsic                   = true                                {C2 product}
     bool UseStoreImmI16                            = false                               {ARCH product}
     bool UseStringDeduplication                    = false                               {product}
     bool UseSuperWord                              = true                                {C2 product}
     bool UseTLAB                                   = true                                {pd product}
     bool UseThreadPriorities                       = true                                {pd product}
     bool UseTransparentHugePages                   = false                               {product}
     bool UseTypeProfile                            = true                                {product}
     bool UseTypeSpeculation                        = true                                {C2 product}
     bool UseUnalignedLoadStores                    = false                               {ARCH product}
     bool UseVMInterruptibleIO                      = false                               {product}
     bool UseXMMForArrayCopy                        = true                                {product}
     bool UseXmmI2D                                 = false                               {ARCH product}
     bool UseXmmI2F                                 = false                               {ARCH product}
     bool UseXmmLoadAndClearUpper                   = true                                {ARCH product}
     bool UseXmmRegToRegMoveAll                     = true             

After running

jcmd [pid] VM.flags

I am getting the below output which also does not specify a collector:

-XX:CICompilerCount=2 -XX:InitialHeapSize=536870912 -XX:MaxHeapSize=536870912 -XX:MaxNewSize=178913280 -XX:MinHeapDeltaBytes=196608 -XX:NewSize=178913280 -XX:OldSize=357957632 -XX:+StartAttachListener -XX:+UseCompressedClassPointers -XX:+UseCompressedOops 

What Is happening here? Is there anything I'm doing wrong?

Answer 1

In JDK 8, if no Use*GC flags are set, and if Parallel GC hasn't been chosen ergonomically, then Serial GC is used.

The fix for JDK-8068582 automatically turns on -XX:+UseSerialGC in such cases since JDK 9.