[SPARK-17714][CORE][TEST-MAVEN][TEST-HADOOP2.6] Avoid using ExecutorClassLoader to load Netty generated classes

## What changes were proposed in this pull request?

Netty's `MessageToMessageEncoder` uses [Javassist](https://github.com/netty/netty/blob/91a0bdc17a8298437d6de08a8958d753799bd4a6/common/src/main/java/io/netty/util/internal/JavassistTypeParameterMatcherGenerator.java#L62) to generate a matcher class and the implementation calls `Class.forName` to check if this class 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 Maven and SBT have different class loader tree. 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 (Note: in maven build, it's loaded into URLClasssLoader so it cannot be found in ExecutorClassLoader). 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` using SBT.

This PR just creates a singleton MessageEncoder and MessageDecoder and makes sure they are created before switching to ExecutorClassLoader. TransportContext will be created when creating RpcEnv and that happens before creating ExecutorClassLoader.

## How was this patch tested?

Jenkins

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #16859 from zsxwing/SPARK-17714.

1 files changed, 4 insertions, 12 deletions

diff --git a/core/src/main/scala/org/apache/spark/util/Utils.scala b/core/src/main/scala/org/apache/spark/util/Utils.scala
index c225e1a0cc..fe6fe6aa4f 100644
--- a/core/src/main/scala/org/apache/spark/util/Utils.scala
+++ b/core/src/main/scala/org/apache/spark/util/Utils.scala
@@ -2608,12 +2608,8 @@ private[util] object CallerContext extends Logging {
   val callerContextSupported: Boolean = {
     SparkHadoopUtil.get.conf.getBoolean("hadoop.caller.context.enabled", false) && {
       try {
-        // `Utils.classForName` will make `ReplSuite` fail with `ClassCircularityError` in
-        // master Maven build, so do not use it before resolving SPARK-17714.
-        // scalastyle:off classforname
-        Class.forName("org.apache.hadoop.ipc.CallerContext")
-        Class.forName("org.apache.hadoop.ipc.CallerContext$Builder")
-        // scalastyle:on classforname
+        Utils.classForName("org.apache.hadoop.ipc.CallerContext")
+        Utils.classForName("org.apache.hadoop.ipc.CallerContext$Builder")
         true
       } catch {
         case _: ClassNotFoundException =>
@@ -2688,12 +2684,8 @@ private[spark] class CallerContext(
   def setCurrentContext(): Unit = {
     if (CallerContext.callerContextSupported) {
       try {
-        // `Utils.classForName` will make `ReplSuite` fail with `ClassCircularityError` in
-        // master Maven build, so do not use it before resolving SPARK-17714.
-        // scalastyle:off classforname
-        val callerContext = Class.forName("org.apache.hadoop.ipc.CallerContext")
-        val builder = Class.forName("org.apache.hadoop.ipc.CallerContext$Builder")
-        // scalastyle:on classforname
+        val callerContext = Utils.classForName("org.apache.hadoop.ipc.CallerContext")
+        val builder = Utils.classForName("org.apache.hadoop.ipc.CallerContext$Builder")
         val builderInst = builder.getConstructor(classOf[String]).newInstance(context)
         val hdfsContext = builder.getMethod("build").invoke(builderInst)
         callerContext.getMethod("setCurrent", callerContext).invoke(null, hdfsContext)