I was struggling to understand a problem with shared classes in Java and I found the options being used by my program were not as I expected.
I thought it would be a very simple task to display at start up options used. It may be, but I could not find how to do it. If anyone knows the simple answer please tell me.
I found one way – take a dump! This seems a little extreme, but it was all I could find. With Liberty you can take a javacore dump (F IZUSVR1,JAVACORE) and display it, or you can take a dump at start up.
In the jvm.options I specified
-Xdump:java:events=vmstart
This gave me in //STDERR
JVMDUMP039I Processing dump event “vmstart”, detail “” at 2021/05/20 13:19:06 – please wait.
JVMDUMP032I JVM requested Java dump using ‘/S0W1/var/…/javacore.20210520.131906.65569.0001.txt’
JVMDUMP010I Java dump written to /S0W1/var…/javacore.20210520.131906.65569.0001.txt
JVMDUMP013I Processed dump event “vmstart”, detail “”.
In this file was list of all the options passed to the JVM
1CIUSERARGS UserArgs:
2CIUSERARG -Xoptionsfile=/usr/lpp/java/J8.0_64/lib/s390x/compressedrefs/options.default
2CIUSERARG -Xlockword:mode=default,noLockword=java/lang/String,noLockword=java/util/Ma
2CIUSERARG -Xjcl:jclse29
2CIUSERARG -Djava.home=/usr/lpp/java/J8.0_64
2CIUSERARG -Djava.ext.dirs=/usr/lpp/java/J8.0_64/lib/ext
2CIUSERARG -Xthr:tw=HEAVY
2CIUSERARG -Xshareclasses:name=liberty-%u,nonfatal,cacheDirPerm=1000,cacheDir=…
2CIUSERARG -XX:ShareClassesEnableBCI
2CIUSERARG -Xscmx60m
2CIUSERARG -Xscmaxaot4m
2CIUSERARG -Xdump:java:events=vmstart
2CIUSERARG -Xscminjitdata5m
2CIUSERARG -Xshareclasses:nonFatal
2CIUSERARG -Xshareclasses:groupAccess
2CIUSERARG -Xshareclasses:cacheDirPerm=0777
2CIUSERARG -Xshareclasses:cacheDir=/tmp,name=zosmf2
2CIUSERARG -Xshareclasses:verbose
2CIUSERARG -Xscmx100m…
the storage limits
1CIUSERLIMITS User Limits (in bytes except for NOFILE and NPROC) NULL ------------------------------------------------------------------------ NULL type soft limit hard limit 2CIUSERLIMIT RLIMIT_AS 1831837696 unlimited 2CIUSERLIMIT RLIMIT_CORE 4194304 4194304 2CIUSERLIMIT RLIMIT_CPU unlimited unlimited 2CIUSERLIMIT RLIMIT_DATA unlimited unlimited 2CIUSERLIMIT RLIMIT_FSIZE unlimited unlimited 2CIUSERLIMIT RLIMIT_NOFILE 10000 10000 2CIUSERLIMIT RLIMIT_STACK unlimited unlimited 2CIUSERLIMIT RLIMIT_MEMLIMIT 4294967296 4294967296
and environment variables used.
1CIENVVARS Environment Variables
2CIENVVAR LOGNAME=IZUSVR
2CIENVVAR _CEE_ENVFILE_S=DD:STDENV
2CIENVVAR _EDC_ADD_ERRNO2=1
2CIENVVAR _EDC_PTHREAD_YIELD=-2
2CIENVVAR WLP_SKIP_MAXPERMSIZE=true
2CIENVVAR _BPX_SHAREAS=NO
2CIENVVAR JAVA_HOME=/usr/lpp/java/J8.0_64…
All interesting stuff including the -X.. parameters. I could see that the parameters I had specified were not being picked up because they were specified higher up! Another face palm moment.
There was a lot more interesting stuff in the file, but this was not relevant to my little problems.
Once z/OSMF was active I took a dump using the f izusvr1,javacore command and looked at the information on the shared classes cache
1SCLTEXTCMST Cache Memory Status 1SCLTEXTCNTD Cache Name Cache path 2SCLTEXTCMDT sharedcc_IZUSVR /tmp/javasharedresources/..._IZUSVR_G37 2SCLTEXTCPF Cache is 85% full 2SCLTEXTCSZ Cache size = 104857040 2SCLTEXTSMB Softmx bytes = 104857040 2SCLTEXTFRB Free bytes = 14936416
This is where I found the shared cache was not what I was expecting! I originally spotted that the cache was too small – and made it bigger.
Afterwards…
Remember to delete the javacore files.
I removed the -Xdump:java:events=vmstart statement, because I found it more convenient to use the f izusvr1,javacore command to take a dump when needed.
ColinPaice 