[SPARK-7288] Suppress compiler warnings due to use of sun.misc.Unsafe; add facade in front of Unsafe; remove use of Unsafe.setMemory

This patch suppresses compiler warnings due to our use of `sun.misc.Unsafe` (introduced in #5725).  These warnings can only be suppressed via the `-XDignore.symbol.file` javac flag; the `SuppressWarnings` annotation won't work for these.

In order to restrict uses of this compiler flag to the `unsafe` module, I placed a facade in front of `Unsafe` so that other modules won't call it directly. This facade also will also help us to avoid accidental usage of deprecated Unsafe methods or methods that aren't supported in Java 6.

I also removed an unnecessary use of `Unsafe.setMemory`, which isn't present in certain versions of Java 6, and excluded the new `unsafe` module from Javadoc.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #5814 from JoshRosen/unsafe-compiler-warnings-fixes and squashes the following commits:

9e8c483 [Josh Rosen] Exclude new unsafe module from Javadoc
ba75ecf [Josh Rosen] Only apply -XDignore.symbol.file flag in unsafe project.
7403345 [Josh Rosen] Put facade in front of Unsafe.
50230c0 [Josh Rosen] Remove usage of Unsafe.setMemory
96d41c9 [Josh Rosen] Use -XDignore.symbol.file to suppress warnings about sun.misc.Unsafe usage

1 files changed, 11 insertions, 0 deletions

diff --git a/project/SparkBuild.scala b/project/SparkBuild.scala
index 4bfa8cede7..a93aa12ce1 100644
--- a/project/SparkBuild.scala
+++ b/project/SparkBuild.scala
@@ -163,6 +163,9 @@ object SparkBuild extends PomBuild {
       x => enable(MimaBuild.mimaSettings(sparkHome, x))(x)
     }
 
+  /* Unsafe settings */
+  enable(Unsafe.settings)(unsafe)
+
   /* Enable Assembly for all assembly projects */
   assemblyProjects.foreach(enable(Assembly.settings))
 
@@ -216,6 +219,13 @@ object SparkBuild extends PomBuild {
 
 }
 
+object Unsafe {
+  lazy val settings = Seq(
+    // This option is needed to suppress warnings from sun.misc.Unsafe usage
+    javacOptions in Compile += "-XDignore.symbol.file"
+  )
+}
+
 object Flume {
   lazy val settings = sbtavro.SbtAvro.avroSettings
 }
@@ -424,6 +434,7 @@ object Unidoc {
       .map(_.filterNot(_.getCanonicalPath.contains("org/apache/spark/network")))
       .map(_.filterNot(_.getCanonicalPath.contains("org/apache/spark/shuffle")))
       .map(_.filterNot(_.getCanonicalPath.contains("org/apache/spark/executor")))
+      .map(_.filterNot(_.getCanonicalPath.contains("org/apache/spark/unsafe")))
       .map(_.filterNot(_.getCanonicalPath.contains("python")))
       .map(_.filterNot(_.getCanonicalPath.contains("org/apache/spark/util/collection")))
       .map(_.filterNot(_.getCanonicalPath.contains("org/apache/spark/sql/catalyst")))