8247619: Improve Direct Buffering of Characters

Reviewed-by: alanb, ahgross, rhalade, psandoz

Author: Brian Burkhalter

src/java.base/share/classes/java/nio/Buffer.java

@@ -313,8 +313,8 @@ public final int position() {
     public Buffer position(int newPosition) {
         if (newPosition > limit | newPosition < 0)
             throw createPositionException(newPosition);
+        if (mark > newPosition) mark = -1;
         position = newPosition;
-        if (mark > position) mark = -1;
         return this;
     }
 
@@ -503,7 +503,8 @@ public Buffer rewind() {
      * @return  The number of elements remaining in this buffer
      */
     public final int remaining() {
-        return limit - position;
+        int rem = limit - position;
+        return rem > 0 ? rem : 0;
     }
 
     /**

src/java.base/share/classes/java/nio/Heap-X-Buffer.java.template

@@ -292,7 +292,9 @@ class Heap$Type$Buffer$RW$
     public $Type$Buffer compact() {
 #if[rw]
         int pos = position();
-        int rem = limit() - pos;
+        int lim = limit();
+        assert (pos <= lim);
+        int rem = (pos <= lim ? lim - pos : 0);
         System.arraycopy(hb, ix(pos), hb, ix(0), rem);
         position(rem);
         limit(capacity());

src/java.base/share/classes/java/nio/X-Buffer.java.template

@@ -452,15 +452,23 @@ public abstract class $Type$Buffer
      */
     public int read(CharBuffer target) throws IOException {
         // Determine the number of bytes n that can be transferred
-        int targetRemaining = target.remaining();
         int limit = limit();
-        int remaining = limit - position();
-        if (remaining == 0)
+        int pos = position();
+        int remaining = limit - pos;
+        assert remaining >= 0;
+        if (remaining <= 0) // include equality condition when remaining == 0
             return -1;
+
+        int targetRemaining = target.remaining();
+        assert targetRemaining >= 0;
+        if (targetRemaining <= 0) // include condition targetRemaining == 0
+            return 0;
+
         int n = Math.min(remaining, targetRemaining);
+
         // Set source limit to prevent target overflow
         if (targetRemaining < remaining)
-            limit(position() + n);
+            limit(pos + n);
         try {
             if (n > 0)
                 target.put(this);
@@ -951,15 +959,19 @@ public abstract class $Type$Buffer
             throw new ReadOnlyBufferException();
 
         int srcPos = src.position();
-        int n = src.limit() - srcPos;
+        int srcLim = src.limit();
+        int srcRem = (srcPos <= srcLim ? srcLim - srcPos : 0);
         int pos = position();
-        if (n > limit() - pos)
+        int lim = limit();
+        int rem = (pos <= lim ? lim - pos : 0);
+
+        if (srcRem > rem)
             throw new BufferOverflowException();
 
-        putBuffer(pos, src, srcPos, n);
+        putBuffer(pos, src, srcPos, srcRem);
 
-        position(pos + n);
-        src.position(srcPos + n);
+        position(pos + srcRem);
+        src.position(srcPos + srcRem);
 
         return this;
     }