Name: vrR10176 Date: 03/21/2001



Api spec says about a view buffer (class java.nio.ByteBuffer):

"A view buffer is potentially much more efficient because it will
be direct if, and only if, its backing byte buffer is direct."

But JVM (jdk1.4.0beta-b56) incorrectly creates in some cases
non-direct view buffers, while its backing byte buffer is direct.

For example,

api spec says (class java.nio.IntBuffer):
"A int buffer created as a view of a byte buffer will be direct
if, and only if, the byte buffer itself is direct."

and (class java.nio.ByteBuffer):
" public abstract IntBuffer asIntBuffer()
     Creates a view of this byte buffer as an int buffer.

The content of the new buffer will start at this buffer's current position.
Changes to this buffer's content will be visible in the new buffer, and vice
versa; the two buffers' position, limit, and mark values will be independent."

If int buffer was created by asIntBuffer() method and its backing byte
buffer is direct, this int buffer must be direct.

But if position of backing byte buffer is 1,2,3,5,...etc (not a multiple of 4),
then asIntBuffer() creates non-direct int buffer, if position is 0,4,...etc
(multiple of 4), then asIntBuffer() creates direct int buffer.
Although all these int buffers must be direct.


Similar behavior is observed for other view buffers (ShortBuffer, FloatBuffer, ...).


To reproduce the issue execute following test.
------------ test.java ------------------------
import java.nio.*;

public class test {
public static void main(String argv[]) {
ByteBuffer buf = ByteBuffer.allocateDirect(8);
System.out.println("Byte buffer is direct: " + buf.isDirect());
for(int i=0; i<6; i++){
buf.position(i);
IntBuffer intBuf = buf.asIntBuffer();
System.out.println("Position: " + i + " Int buffer is direct: " + intBuf.isDirect());
}
}
}

------------ Logs ------------------------
$ java -version
java version "1.4.0-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-beta-b56)
Java HotSpot(TM) Client VM (build 1.4-beta-B56, mixed mode)

$javac test.java

$java -Xfuture test
Byte buffer is direct: true
Position: 0 Int buffer is direct: true
Position: 1 Int buffer is direct: false
Position: 2 Int buffer is direct: false
Position: 3 Int buffer is direct: false
Position: 4 Int buffer is direct: true
Position: 5 Int buffer is direct: false

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