GitHub user zsxwing opened a pull request:
https://github.com/apache/spark/pull/16859
[SPARK-17714][Core][maven]Avoid using ExecutorClassLoader to load Netty
generated classes
## What changes were proposed in this pull request?
Netty's `MessageToMessageEncoder` uses Javassist to generate a matcher
class and the implementation calls `Class.forName` to check if this calls is
already generated. If `MessageEncoder` or `MessageDecoder` is created in
`ExecutorClassLoader.findClass`, it will cause `ClassCircularityError`. This is
because loading this Netty generated class will call
`ExecutorClassLoader.findClass` to search this class, and `ExecutorClassLoader`
will try to use RPC to load it and cause to load the non-exist matcher class
again. JVM will report `ClassCircularityError` to prevent such infinite
recursion.
##### Why it only happens in Maven builds
It's because the Maven build will set a URLClassLoader as the current
context class loader to run the tests and expose this issue. The class loader
tree is as following:
```
bootstrap class loader ------ ... ----- REPL class loader ----
ExecutorClassLoader
|
|
URLClasssLoader
```
The SBT build uses the bootstrap class loader directly and
`ReplSuite.test("propagation of local properties")` is the first test in
ReplSuite, which happens to load
`io/netty/util/internal/__matchers__/org/apache/spark/network/protocol/MessageMatcher`
into the bootstrap class loader. This issue can be reproduced in SBT as well.
Here are the produce steps:
- Enable `hadoop.caller.context.enabled`.
- Replace `Class.forName` with `Utils.classForName` in `object
CallerContext`.
- Ignore `ReplSuite.test("propagation of local properties")`.
- Run `ReplSuite`.
This PR just creates a singleton MessageEncoder and MessageDecoder and
makes sure they can be created before switching to ExecutorClassLoader.
TransportContext will be created when creating RpcEnv and that happens before
creating ExecutorClassLoader.
## How was this patch tested?
Jenkins
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/zsxwing/spark SPARK-17714
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/16859.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #16859
----
commit 1c8847494c29d4b51182ecfeebb5cc85e000e7a1
Author: Shixiong Zhu <shixi...@databricks.com>
Date: 2017-02-07T22:30:42Z
Avoid using ExecutorClassLoader to load Netty generated classes
----
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