This section provides implementation specific information for deploying JAR files when not using classloader isolation. Chained class loading was the default in GemFire v9, and is provided for legacy support.
Classloader isolation can be disabled using the flag
--disable-classloader-isolation=true when starting servers through Gfsh using the
start server command. With the non-classloader isolated, or chained, approach, JAR files are loaded into classloaders which are chained together with the system classloader where they are able to access other classes in the hierarchy.
For information common between all deployment implementation, read Deploying Application Jars.
The system location where JAR files are written on each member is determined by the
deploy-working-dir GemFire property configured for that member. For example, you could have the following configured in the
gemfire.properties file for your member:
This deployment location can be local or a shared network resource (such as a mount location) used by multiple members in order to reduce disk space usage. If you use a shared directory, you still need to deploy the JAR file on every member that you want to have access to the application, because deployment updates the CLASSPATH and auto-registers functions.
When you deploy JAR files to a cluster or member group, the JAR file is modified to indicate version information in its name. Each JAR filename contains a version number inserted just before the
.jar suffix. For example, if you deploy
MyClasses.jar five times, the filename is displayed as
MyClasses.v5.jar when you list all deployed JAR files.
When you deploy a new JAR file, the member receiving the deployment checks whether the JAR file is a duplicate, either because the JAR file has already been deployed on that member or because the JAR file has already been deployed to a shared deployment working directory that other members are also using. If another member has already deployed this JAR file to the shared directory (determined by doing a byte-for-byte compare to the latest version in its directory), the member receiving the latest deployment does not write the file to disk. Instead, the member updates the ClassPathLoader to use the already deployed JAR file. If a newer version of the JAR file is detected on disk and is already in use, the deployment is canceled.
When a member begins using a JAR file, the member obtains a shared lock on the file. If the member receives a newer version by deployment, the member releases the shared lock and tries to delete the existing JAR file in favor of the newer version. If no other member has a shared lock on the existing JAR, the existing, older version JAR is deleted.
When a cache is started, the new cache requests that the latest versions of each JAR file in the current working directory be added to the ClassPathLoader. If a JAR file has already been deployed to the ClassPathLoader, the ClassPathLoader updates its loaded version if a newer version is found; otherwise, there is no change. If detected, older versions of the JAR files are deleted if no other member has a shared lock on them.
Undeploying a JAR file does not automatically unload the classes that were loaded during deployment. You need to restart your members to unload those classes.
When a cache is closed it requests that all currently deployed JAR files be removed from the ClassPathLoader.
If you are using a shared deployment working directory, all members sharing the directory should belong to the same member group. Upon restart, all members that share the same deployment working directory will deploy and autoload their CLASSPATH with any JARs found in the current working directory. This means that some members may load the JARs even though they are not part of the member group that received the original deployment.