--- a/jdk/src/share/classes/sun/nio/ch/IOVecWrapper.java	Tue Aug 10 13:15:40 2010 -0700
+++ b/jdk/src/share/classes/sun/nio/ch/IOVecWrapper.java	Thu Aug 12 19:53:25 2010 +0100
@@ -25,6 +25,7 @@
 
 package sun.nio.ch;
 
+import java.nio.ByteBuffer;
 import sun.misc.*;
 
 
@@ -43,23 +44,98 @@
 class IOVecWrapper {
 
     // Miscellaneous constants
-    static int BASE_OFFSET = 0;
-    static int LEN_OFFSET;
-    static int SIZE_IOVEC;
+    private static final int BASE_OFFSET = 0;
+    private static final int LEN_OFFSET;
+    private static final int SIZE_IOVEC;
 
     // The iovec array
-    private AllocatedNativeObject vecArray;
+    private final AllocatedNativeObject vecArray;
+
+    // Number of elements in iovec array
+    private final int size;
+
+    // Buffers and position/remaining corresponding to elements in iovec array
+    private final ByteBuffer[] buf;
+    private final int[] position;
+    private final int[] remaining;
+
+    // Shadow buffers for cases when original buffer is substituted
+    private final ByteBuffer[] shadow;
 
     // Base address of this array
-    long address;
+    final long address;
 
     // Address size in bytes
     static int addressSize;
 
-    IOVecWrapper(int newSize) {
-        newSize = (newSize + 1) * SIZE_IOVEC;
-        vecArray = new AllocatedNativeObject(newSize, false);
-        address = vecArray.address();
+    private static class Deallocator implements Runnable {
+        private final AllocatedNativeObject obj;
+        Deallocator(AllocatedNativeObject obj) {
+            this.obj = obj;
+        }
+        public void run() {
+            obj.free();
+        }
+    }
+
+    // per thread IOVecWrapper
+    private static final ThreadLocal<IOVecWrapper> cached =
+        new ThreadLocal<IOVecWrapper>();
+
+    private IOVecWrapper(int size) {
+        this.size      = size;
+        this.buf       = new ByteBuffer[size];
+        this.position  = new int[size];
+        this.remaining = new int[size];
+        this.shadow    = new ByteBuffer[size];
+        this.vecArray  = new AllocatedNativeObject(size * SIZE_IOVEC, false);
+        this.address   = vecArray.address();
+    }
+
+    static IOVecWrapper get(int size) {
+        IOVecWrapper wrapper = cached.get();
+        if (wrapper != null && wrapper.size < size) {
+            // not big enough; eagerly release memory
+            wrapper.vecArray.free();
+            wrapper = null;
+        }
+        if (wrapper == null) {
+            wrapper = new IOVecWrapper(size);
+            Cleaner.create(wrapper, new Deallocator(wrapper.vecArray));
+            cached.set(wrapper);
+        }
+        return wrapper;
+    }
+
+    void setBuffer(int i, ByteBuffer buf, int pos, int rem) {
+        this.buf[i] = buf;
+        this.position[i] = pos;
+        this.remaining[i] = rem;
+    }
+
+    void setShadow(int i, ByteBuffer buf) {
+        shadow[i] = buf;
+    }
+
+    ByteBuffer getBuffer(int i) {
+        return buf[i];
+    }
+
+    int getPosition(int i) {
+        return position[i];
+    }
+
+    int getRemaining(int i) {
+        return remaining[i];
+    }
+
+    ByteBuffer getShadow(int i) {
+        return shadow[i];
+    }
+
+    void clearRefs(int i) {
+        buf[i] = null;
+        shadow[i] = null;
     }
 
     void putBase(int i, long base) {
@@ -78,10 +154,6 @@
             vecArray.putLong(offset, len);
     }
 
-    void free() {
-        vecArray.free();
-    }
-
     static {
         addressSize = Util.unsafe().addressSize();
         LEN_OFFSET = addressSize;