[GitHub] [rocketmq] JerryChaox commented on issue #1718: Switching from CMS to G1

[GitBox <gi...@apache.org>]

JerryChaox commented on issue #1718: Switching from CMS to G1
URL: https://github.com/apache/rocketmq/issues/1718#issuecomment-593444788
 
 
   > I performed verification tests. There is no problem with GC switching, but high-level JDK （after JDK1.8）is not supported because of modularity and class loader.
   > 我进行了验证测试，GC替换没有问题，但是由于模块化和类加载器等原因，高版本JDK不支持。
   
   According to the migration guide:
   
   1. https://docs.oracle.com/javase/9/migrate/toc.htm#JSMIG-GUID-A78CC891-701D-4549-AA4E-B8DD90228B4B
   2. https://docs.oracle.com/en/java/javase/11/migrate/index.html#JSMIG-GUID-A78CC891-701D-4549-AA4E-B8DD90228B4B
   
   Starting from JDK 9
   > Class and resource files previously stored in lib/rt.jar, lib/tools.jar, lib/dt.jar and various other internal JAR files are stored in a more efficient format in implementation-specific files in the lib directory.
   
   >The javac compiler and java launcher will exit if the java.ext.dirs system property is set, or if the lib/ext directory exists. To additionally check the platform-specific systemwide directory, specify the -XX:+CheckEndorsedAndExtDirs command-line option. This causes the same exit behavior to occur if the directory exists and isn’t empty. The extension class loader is retained in JDK 9 and is specified as the platform class loader (see getPlatformClassLoader.)
   
   So starting from jdk9, it's necessary to remove this line for JAVA_OPT:
   `JAVA_OPT="${JAVA_OPT} -Djava.ext.dirs=${JAVA_HOME}/jre/lib/ext:${BASE_DIR}/lib"`
   and rocketmq does not need the extension mechanism.
   
   Moreover, it's necessary to check if rocketmq break the rules of this new specification (JEP220).
   
   [See JEP 220: Modular Run-Time Images. ](http://openjdk.java.net/jeps/220)
   
   
   

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