Revert "in DirectByteBufferPool keep buffers by soft reference"

akka-io/src/main/scala/akka/io/DirectByteBufferPool.scala

@@ -3,7 +3,6 @@ package akka.io
 import java.util.concurrent.atomic.AtomicBoolean
 import java.nio.ByteBuffer
 import annotation.tailrec
-import java.lang.ref.SoftReference
 
 trait WithBufferPool {
   def tcp: TcpExt
@@ -29,20 +28,11 @@ trait BufferPool {
  */
 private[akka] class DirectByteBufferPool(defaultBufferSize: Int, maxPoolEntries: Int) extends BufferPool {
   private[this] val locked = new AtomicBoolean(false)
-  private[this] val pool: Array[SoftReference[ByteBuffer]] = new Array[SoftReference[ByteBuffer]](maxPoolEntries)
+  private[this] val pool: Array[ByteBuffer] = new Array[ByteBuffer](maxPoolEntries)
   private[this] var buffersInPool: Int = 0
 
-  def acquire(): ByteBuffer = {
-    val buffer = takeBufferFromPool()
-
-    // allocate new buffer and clear outside the lock
-    if (buffer == null)
-      allocate(defaultBufferSize)
-    else {
-      buffer.clear()
-      buffer
-    }
-  }
+  def acquire(): ByteBuffer =
+    takeBufferFromPool()
 
   def release(buf: ByteBuffer): Unit =
     offerBufferToPool(buf)
@@ -51,26 +41,29 @@ private[akka] class DirectByteBufferPool(defaultBufferSize: Int, maxPoolEntries:
     ByteBuffer.allocateDirect(size)
 
   @tailrec
-  private[this] final def takeBufferFromPool(): ByteBuffer = {
-    @tailrec def findBuffer(): ByteBuffer =
-      if (buffersInPool > 0) {
-        buffersInPool -= 1
-        val buf = pool(buffersInPool).get()
+  private final def takeBufferFromPool(): ByteBuffer =
+    if (locked.compareAndSet(false, true)) {
+      val buffer =
+        try if (buffersInPool > 0) {
+          buffersInPool -= 1
+          pool(buffersInPool)
+        } else null
+        finally locked.set(false)
 
-        if (buf != null) buf
-        else findBuffer()
-      } else null
-
-    if (locked.compareAndSet(false, true))
-      try findBuffer() finally locked.set(false)
-    else takeBufferFromPool() // spin while locked
-  }
+      // allocate new and clear outside the lock
+      if (buffer == null)
+        allocate(defaultBufferSize)
+      else {
+        buffer.clear()
+        buffer
+      }
+    } else takeBufferFromPool() // spin while locked
 
   @tailrec
   private final def offerBufferToPool(buf: ByteBuffer): Unit =
     if (locked.compareAndSet(false, true))
       try if (buffersInPool < maxPoolEntries) {
-        pool(buffersInPool) = new SoftReference(buf)
+        pool(buffersInPool) = buf
         buffersInPool += 1
       } // else let the buffer be gc'd
       finally locked.set(false)