Update a few comments (minor)

Author: andrewor14

bin/spark-class2.cmd

@@ -127,7 +127,7 @@ if not "x%JAVA_HOME%"=="x" set RUNNER=%JAVA_HOME%\bin\java
 
 rem In Spark submit client mode, the driver is launched in the same JVM as Spark submit itself.
 rem Here we must parse the properties file for relevant "spark.driver.*" configs before launching
-rem the driver JVM itself. Instead of handling this complexity in Bash, we launch a separate JVM
+rem the driver JVM itself. Instead of handling this complexity here, we launch a separate JVM
 rem to prepare the launch environment of this driver JVM.
 
 rem In this case, leave out the main class (org.apache.spark.deploy.SparkSubmit) and use our own.

bin/spark-submit.cmd

@@ -29,7 +29,6 @@ set SPARK_SUBMIT_DRIVER_MEMORY=
 set SPARK_SUBMIT_LIBRARY_PATH=
 set SPARK_SUBMIT_CLASSPATH=
 set SPARK_SUBMIT_OPTS=
-set SPARK_DRIVER_MEMORY=
 set SPARK_SUBMIT_BOOTSTRAP_DRIVER=
 
 :loop

core/src/main/scala/org/apache/spark/deploy/SparkSubmitDriverBootstrapper.scala

@@ -139,7 +139,7 @@ private[spark] object SparkSubmitDriverBootstrapper {
     stderrThread.start()
 
     // In Windows, the subprocess reads directly from our stdin, so we should avoid spawning
-    // a thread that also reads from stdin and contends with the subprocess.
+    // a thread that contends with the subprocess in reading from System.in.
     if (Utils.isWindows) {
       // For the PySpark shell, the termination of this process is handled in java_gateway.py
       process.waitFor()

python/pyspark/java_gateway.py

@@ -70,7 +70,7 @@ def preexec_func():
                 error_msg += "--------------------------------------------------------------\n"
             raise Exception(error_msg)
 
-        # Ensure the Java child processes do not linger after python has exited in Windows.
+        # In Windows, ensure the Java child processes do not linger after Python has exited.
         # In UNIX-based systems, the child process can kill itself on broken pipe (i.e. when
         # the parent process' stdin sends an EOF). In Windows, however, this is not possible
         # because java.lang.Process reads directly from the parent process' stdin, contending
@@ -81,7 +81,7 @@ def preexec_func():
             # (because the UNIX "exec" command is not available). This means we cannot simply
             # call proc.kill(), which kills only the "spark-submit.cmd" process but not the
             # JVMs. Instead, we use "taskkill" with the tree-kill option "/t" to terminate all
-            # child processes.
+            # child processes in the tree.
             def killChild():
                 Popen(["cmd", "/c", "taskkill", "/f", "/t", "/pid", str(proc.pid)])
             atexit.register(killChild)