Switch to OpenJ9 base image (#360)

Dockerfile

@@ -1,4 +1,4 @@
-FROM openjdk:8u212-jre-alpine
+FROM adoptopenjdk/openjdk8-openj9:alpine
 
 LABEL maintainer "itzg"
 
@@ -75,7 +75,7 @@ WORKDIR /data
 ENTRYPOINT [ "/start" ]
 
 ENV UID=1000 GID=1000 \
-  JVM_XX_OPTS="-XX:+UseG1GC" MEMORY="1G" \
+  MEMORY="1G" \
   TYPE=VANILLA VERSION=LATEST FORGEVERSION=RECOMMENDED SPONGEBRANCH=STABLE SPONGEVERSION= FABRICVERSION=LATEST LEVEL=world \
   PVP=true DIFFICULTY=easy ENABLE_RCON=true RCON_PORT=25575 RCON_PASSWORD=minecraft \
   LEVEL_TYPE=DEFAULT GENERATOR_SETTINGS= WORLD= MODPACK= MODS= SERVER_PORT=25565 ONLINE_MODE=TRUE CONSOLE=true SERVER_NAME="Dedicated Server" \

README.md

@@ -1015,6 +1015,14 @@ via a `JVM_XX_OPTS` environment variable.
 For some cases, if e.g. after removing mods, it could be necessary to startup minecraft with an additional `-D` parameter like `-Dfml.queryResult=confirm`. To address this you can use the environment variable `JVM_DD_OPTS`, which builds the params from a given list of values separated by space, but without the `-D` prefix. To make things running under systems (e.g. Plesk), which doesn't allow `=` inside values, a `:` (colon) could be used instead. The upper example would look like this:
 `JVM_DD_OPTS=fml.queryResult:confirm`, and will be converted to `-Dfml.queryResult=confirm`. 
 
+The container uses [OpenJ9](https://www.eclipse.org/openj9/docs) and a couple of J9 options are
+simplified by environment variables:
+
+- `-e TUNE_VIRTUALIZED=TRUE` : enables the option to 
+  [optimize for virtualized environments](https://www.eclipse.org/openj9/docs/xtunevirtualized/)
+- `-e TUNE_NURSERY_SIZES=TRUE` : configures nursery sizes where the initial size is 50%
+  of the `MAX_MEMORY` and the max size is 80%.
+
 ### HTTP Proxy
 
 You may configure the use of an HTTP/HTTPS proxy by passing the proxy's URL via the `PROXY`

start-minecraftFinalSetup

@@ -84,6 +84,23 @@ if [ -n "$JVM_DD_OPTS" ]; then
       done
 fi
 
+if isTrue ${TUNE_VIRTUALIZED}; then
+  JVM_XX_OPTS="${JVM_XX_OPTS} -Xtune:virtualized"
+fi
+
+if isTrue ${TUNE_NURSERY_SIZES}; then
+  case ${MAX_MEMORY^^} in
+    *G)
+      MAX_MEMORY_MB=$(( ${MAX_MEMORY%?} * 1024 )) ;;
+    *M)
+      MAX_MEMORY_MB=${MAX_MEMORY%?} ;;
+  esac
+
+  NURSERY_MINIMUM=$(( ${MAX_MEMORY_MB} / 2 ))
+  NURSERY_MAXIMUM=$(( ${MAX_MEMORY_MB} * 4/5 ))
+  JVM_XX_OPTS="${JVM_XX_OPTS} -Xmns${NURSERY_MINIMUM}M -Xmnx${NURSERY_MAXIMUM}M"
+fi
+
 mcServerRunnerArgs="--stop-duration 60s"
 
 if [[ ${TYPE} == "FEED-THE-BEAST" ]]; then