Elek, Marton created HDDS-1080:
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Summary: Ozonefs Isolated class loader should support
FsStorageStatistics
Key: HDDS-1080
URL: https://issues.apache.org/jira/browse/HDDS-1080
Project: Hadoop Distributed Data Store
Issue Type: Improvement
Components: Ozone Filesystem
Reporter: Elek, Marton
Assignee: Elek, Marton
Attachments: HDDS-1080.001.patch
HDDS-1033 introduced the storage statistics for ozonefs. Unfortunately the
isolated classloader (HDDS-922) doesn't work any more after this change.
To explain the problem, let's use the specific expression
_classname[classloader]_ for a class (named by classname) which is loaded by
the classloader.
We have two classloaders the _main_ which is the standard classloader of the
application and the _isolated_ classloader which is created by the
OzoneClientAdapterFactory.java.
By default java classloaders delegate the loading to the parent class loader,
and they load all the classes from the parent first (if possible). The isolated
class loader does the oposit, loads all the classes from a specific location of
the jar files. With this approach we can use hadoop3.2+ozone classes together
with older hadoop versions.
But back to the problem:
OzoneFilesystem[main] is loaded by the application. In this class an
OzoneFSStorageStatistics[main] is created and with the help of
OzoneClientAdapterFactory[main] a new OzoneClientAdapterImpl[isolated!!] is
instantiated which implements the OzoneClientAdapter[main] and will do all the
main work[isolated].
OzoneClientAdapterImp[isolated] has a new constructor which requires
(String[system], String[system], OzoneFSStorageStatistics[isolated]).
And this is the problem, it requires OzoneFSStorageStatistics[isolated] but we
have a OzoneFSStorageStatistics[main].
The fix is very straightforward. In the FilteredClassLoader.java we ha a list
for the classes which should be shared by the two classloaders. For these
classes the isolated classloader will delegate the loading to the parent
([main]) classloader and we will have one (and only one)
OzoneFSStorageStatistics[main] everywhere.
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