Staticly initialize DirectByteBuffer constructor

Java reflection is quite expensive (https://docs.oracle.com/javase/tutorial/reflect/index.html):

"Because reflection involves types that are dynamically resolved, certain Java virtual machine optimizations can not be performed.
 Consequently, reflective operations have slower performance than their non-reflective counterparts,
 and should be avoided in sections of code which are called frequently in performance-sensitive applications."

In critical path we call getByteBuffer quite frequently: https://user-images.githubusercontent.com/1121987/47508402-bcce9680-d87c-11e8-99d2-7b55677e4d3e.png

So we could statically initialize ByteBuffer constructor reflection, and only instantiate it based on the arguments.

Change-Id: Ibca8ddbd67c4239a6e462a453669b7519c89afc8

Author: petro-rudenko

src/main/java/org/apache/spark/shuffle/rdma/RdmaBuffer.java

@@ -40,7 +40,18 @@ class RdmaBuffer {
   private final MemoryBlock block;
   private AtomicInteger refCount;
 
-  public static final UnsafeMemoryAllocator unsafeAlloc = new UnsafeMemoryAllocator();
+  static final UnsafeMemoryAllocator unsafeAlloc = new UnsafeMemoryAllocator();
+  public static final Constructor<?> directBufferConstructor;
+
+  static {
+    try {
+      Class<?> classDirectByteBuffer = Class.forName("java.nio.DirectByteBuffer");
+      directBufferConstructor = classDirectByteBuffer.getDeclaredConstructor(long.class, int.class);
+      directBufferConstructor.setAccessible(true);
+    } catch (Exception e) {
+      throw new RuntimeException("java.nio.DirectByteBuffer class not found");
+    }
+  }
 
   RdmaBuffer(IbvPd ibvPd, int length) throws IOException {
     block = unsafeAlloc.allocate((long)length);
@@ -126,25 +137,10 @@ private void unregister() {
   }
 
   ByteBuffer getByteBuffer() throws IOException {
-    Class<?> classDirectByteBuffer;
-    try {
-      classDirectByteBuffer = Class.forName("java.nio.DirectByteBuffer");
-    } catch (ClassNotFoundException e) {
-      throw new IOException("java.nio.DirectByteBuffer class not found");
-    }
-    Constructor<?> constructor;
-    try {
-      constructor = classDirectByteBuffer.getDeclaredConstructor(long.class, int.class);
-    } catch (NoSuchMethodException e) {
-      throw new IOException("java.nio.DirectByteBuffer constructor not found");
-    }
-    constructor.setAccessible(true);
-    ByteBuffer byteBuffer;
     try {
-      byteBuffer = (ByteBuffer)constructor.newInstance(getAddress(), getLength());
+      return (ByteBuffer)directBufferConstructor.newInstance(getAddress(), getLength());
     } catch (Exception e) {
       throw new IOException("java.nio.DirectByteBuffer exception: " + e.toString());
     }
-    return byteBuffer;
   }
 }

src/main/java/org/apache/spark/shuffle/rdma/RdmaMappedFile.java

@@ -200,30 +200,14 @@ public void dispose() throws IOException, InvocationTargetException, IllegalAcce
   }
 
   private ByteBuffer getByteBuffer(long address, int length) throws IOException {
-    Class<?> classDirectByteBuffer;
     try {
-      classDirectByteBuffer = Class.forName("java.nio.DirectByteBuffer");
-    } catch (ClassNotFoundException e) {
-      throw new IOException("java.nio.DirectByteBuffer class not found");
-    }
-    Constructor<?> constructor;
-    try {
-      constructor = classDirectByteBuffer.getDeclaredConstructor(long.class, int.class);
-    } catch (NoSuchMethodException e) {
-      throw new IOException("java.nio.DirectByteBuffer constructor not found");
-    }
-    constructor.setAccessible(true);
-    ByteBuffer byteBuffer;
-    try {
-      byteBuffer = (ByteBuffer)constructor.newInstance(address, length);
+      return (ByteBuffer)RdmaBuffer.directBufferConstructor.newInstance(address, length);
     } catch (InvocationTargetException ex) {
       throw new IOException("java.nio.DirectByteBuffer: " +
         "InvocationTargetException: " + ex.getTargetException());
     } catch (Exception e) {
       throw new IOException("java.nio.DirectByteBuffer exception: " + e.toString());
     }
-
-    return byteBuffer;
   }
 
   public ByteBuffer getByteBufferForPartition(int partitionId) throws IOException {

src/main/java/org/apache/spark/shuffle/rdma/RdmaRegisteredBuffer.java

@@ -18,7 +18,6 @@
 package org.apache.spark.shuffle.rdma;
 
 import java.io.IOException;
-import java.lang.reflect.Constructor;
 import java.nio.ByteBuffer;
 import java.util.concurrent.atomic.AtomicInteger;
 
@@ -75,22 +74,9 @@ ByteBuffer getByteBuffer(int length) throws IOException {
       throw new IllegalArgumentException("Exceeded Registered Length!");
     }
 
-    Class<?> classDirectByteBuffer;
-    try {
-      classDirectByteBuffer = Class.forName("java.nio.DirectByteBuffer");
-    } catch (ClassNotFoundException e) {
-      throw new IOException("java.nio.DirectByteBuffer class not found");
-    }
-    Constructor<?> constructor;
-    try {
-      constructor = classDirectByteBuffer.getDeclaredConstructor(long.class, int.class);
-    } catch (NoSuchMethodException e) {
-      throw new IOException("java.nio.DirectByteBuffer constructor not found");
-    }
-    constructor.setAccessible(true);
     ByteBuffer byteBuffer;
     try {
-      byteBuffer = (ByteBuffer)constructor.newInstance(
+      byteBuffer = (ByteBuffer)RdmaBuffer.directBufferConstructor.newInstance(
         getRegisteredAddress() + (long)blockOffset, length);
       blockOffset += length;
     } catch (Exception e) {