Change newURI to uriOf and add some comments

Author: zsxwing

core/src/main/scala/org/apache/spark/deploy/worker/WorkerWatcher.scala

@@ -37,6 +37,10 @@ private[spark] class WorkerWatcher(override val rpcEnv: RpcEnv, workerUrl: Strin
   }
 
   // Used to avoid shutting down JVM during tests
+  // In the normal case, exitNonZero will call `System.exit(-1)` to shutdown the JVM. In the unit
+  // test, the user should call `setTesting(true)` so that `exitNonZero` will set `isShutDown` to
+  // true rather than calling `System.exit`. The user can check `isShutDown` to know if
+  // `exitNonZero` is called.
   private[deploy] var isShutDown = false
   private[deploy] def setTesting(testing: Boolean) = isTesting = testing
   private var isTesting = false

core/src/main/scala/org/apache/spark/rpc/ActionScheduler.scala

@@ -66,7 +66,10 @@ private[spark] trait ActionScheduler {
 }
 
 private[spark] trait Cancellable {
-  // Should be reentrant
+  /**
+   * Cancel the corresponding work. The caller may call this method multiple times and call it in
+   * any thread.
+   */
   def cancel(): Unit
 }
 

core/src/main/scala/org/apache/spark/rpc/RpcEnv.scala

@@ -84,7 +84,7 @@ private[spark] trait RpcEnv {
   /**
    * Create a URI used to create a [[RpcEndpointRef]]
    */
-  def newURI(systemName: String, address: RpcAddress, endpointName: String): String
+  def uriOf(systemName: String, address: RpcAddress, endpointName: String): String
 }
 
 private[spark] case class RpcEnvConfig(

core/src/main/scala/org/apache/spark/rpc/akka/AkkaRpcEnv.scala

@@ -172,6 +172,10 @@ private[spark] class AkkaRpcEnv private (
     }
   }
 
+  /**
+   * Run `action` safely to avoid to crash the thread. If any non-fatal exception happens, it will
+   * call `endpoint.onError`. If `endpoint.onError` throws any non-fatal exception, just log it.
+   */
   private def safelyCall(endpoint: RpcEndpoint)(action: => Unit): Unit = {
     try {
       action
@@ -204,10 +208,10 @@ private[spark] class AkkaRpcEnv private (
 
   override def setupEndpointRef(
       systemName: String, address: RpcAddress, endpointName: String): RpcEndpointRef = {
-    setupEndpointRefByUrl(newURI(systemName, address, endpointName))
+    setupEndpointRefByUrl(uriOf(systemName, address, endpointName))
   }
 
-  override def newURI(systemName: String, address: RpcAddress, endpointName: String): String = {
+  override def uriOf(systemName: String, address: RpcAddress, endpointName: String): String = {
     AkkaUtils.address(
       AkkaUtils.protocol(actorSystem), systemName, address.host, address.port, endpointName)
   }