On 10/23/2014 10:16 AM, Stanimir Simeonoff wrote:
Unsafe is available, so the fields (array, offset) can be read directly
UNSAFE.getObject(buffer, hbOffset), UNSAFE.getObject(buffer, offsetOffset).
No need for MethodHandlers.
During class init the offsets have to be resolved, pretty much like any CAS
utilizing algorithm.
I didn't propose it as readOnlyBuffers are very, very rarely used and even
more unlikely to be used to calculate checksums. It just makes the code
ugly.
Agreed. And when Staffan introduces intrinsic, he could pass the
ByteBuffer instance to it and extract the byte[] there...
Peter
Stanimir
On Thu, Oct 23, 2014 at 11:05 AM, Peter Levart <peter.lev...@gmail.com>
wrote:
On 10/23/2014 03:52 AM, Staffan Friberg wrote:
Webrev with these last updates. Added more tests to make sure CRC32C,
CRC32 and Checksum default methods all are covered.
http://cr.openjdk.java.net/~sfriberg/JDK-6321472/webrev.07
Hi Staffan,
Regarding default case:
168 } else {
169 byte[] b = new byte[Math.min(buffer.remaining(), 4096)];
170 while (buffer.hasRemaining()) {
171 int length = Math.min(buffer.remaining(), b.length);
172 buffer.get(b, 0, length);
173 update(b, 0, length);
174 }
175 }
Have you tried using get()/getInt() directly on the (ro) ByteBuffer
instead of copying to byte[] chunks? Intuitively one would expect it
perform faster if a redundant copy is avoided. Ah, you already told us that
you plan to use intrinsic for CRC32C in the future, so you want to have
"addresses" at hand.
A hackish way to avoid copying in this case is to access the byte[] and
offset using reflection. But this would have to be wrapped with
doPrivileged() which would worsen performance for small buffers. A way to
avoid repeated access checks is to do them at class initialization time,
using MethodHandle(s). For example, something like:
private static final MethodHandle bbArrayGetter;
private static final MethodHandle bbArrayOffsetGetter;
static {
MethodHandle hbGetter;
MethodHandle offsetGetter;
try {
Field hbField = ByteBuffer.class.getDeclaredField("hb");
Field offsetField = ByteBuffer.class.
getDeclaredField("offset");
AccessController.doPrivileged(new PrivilegedAction<Void>() {
@Override
public Void run() {
hbField.setAccessible(true);
offsetField.setAccessible(true);
return null;
}
});
hbGetter = MethodHandles.lookup().unreflectGetter(hbField);
offsetGetter = MethodHandles.lookup().
unreflectGetter(offsetField);
} catch (NoSuchFieldException | IllegalAccessException e) {
hbGetter = null;
offsetGetter = null;
}
bbArrayGetter = hbGetter;
bbArrayOffsetGetter = offsetGetter;
}
private static byte[] getArrayOrNull(ByteBuffer bb) {
if (bb.hasArray()) return bb.array();
if (bbArrayGetter != null) {
try {
return (byte[]) bbArrayGetter.invokeExact(bb);
} catch (Throwable e) {
throw new InternalError(e);
}
}
return null;
}
private static int getArrayOffset(ByteBuffer bb) {
if (bb.hasArray()) return bb.arrayOffset();
if (bbArrayOffsetGetter != null) {
try {
return (int) bbArrayOffsetGetter.invokeExact(bb);
} catch (Throwable e) {
throw new InternalError(e);
}
}
throw new UnsupportedOperationException();
}
Regards, Peter
//Staffan
On 10/22/2014 05:37 PM, Stanimir Simeonoff wrote:
Hi Staffan,
The readonly buffer (ByteBuffer.asReadOnlyBuffer()) don't have array()
"working".
You can use "int length = Math.min(buffer.remaining, b.length)" instead,
same with new byte[Math.min(4096, buffer.remaining)]. Using smaller chunks
will be more performance friendly than allocating/eating up a huge byte[].
If you feel like, add a test with a heap bytebuffer.asReadOnlyBuffer().
Stanimir
On Thu, Oct 23, 2014 at 3:06 AM, Staffan Friberg <
staffan.frib...@oracle.com <mailto:staffan.frib...@oracle.com>> wrote:
Hi,
I was thinking about this earlier when I started writing the patch
and then I forgot about it again. I haven't been able to figure
out when the code will be executed. ByteBuffer is implemented in
such a way that only the JDK can extend it and as far as I can
tell you can only create 3 types of ByteBuffers (Direct, Mapped
and Heap), all of which will be handled by the more efficient
calls above.
That said just to make the code a bit safer from OOM it is
probably best to update the default method and all current
implementations which all use the same pattern.
A reasonable solution should be the following code
byte[] b = new byte[(buffer.remaining() < 4096)
? buffer.remaining() : 4096];
while (buffer.hasRemaining()) {
int length = (buffer.remaining() < b.length)
? buffer.remaining() : b.length;
buffer.get(b, 0, length);
update(b, 0, length);
}
Xueming, do you have any further comment?
Regards,
Staffan
On 10/22/2014 03:04 PM, Stanimir Simeonoff wrote:
On Thu, Oct 23, 2014 at 12:10 AM, Bernd Eckenfels
<e...@zusammenkunft.net <mailto:e...@zusammenkunft.net>> wrote:
Hello,
just a question in the default impl:
+ } else {
+ byte[] b = new byte[rem];
+ buffer.get(b);
+ update(b, 0, b.length);
+ }
would it be a good idea to actually put a ceiling on the size
of the
array which is processed at once?
This is an excellent catch.
Should not be too large, probably 4k or so.
Stanimir
Am Tue, 21 Oct 2014 10:28:50 -0700
schrieb Staffan Friberg <staffan.frib...@oracle.com
<mailto:staffan.frib...@oracle.com>>:
> Hi Peter,
>
> Thanks for the comments..
> >
> > 217 if (Unsafe.ADDRESS_SIZE == 4) {
> > 218 // On 32 bit platforms read two
ints
> > instead of a single 64bit long
> >
> > When you're reading from byte[] using Unsafe
(updateBytes), you
> > have the option of reading 64bit values on 64bit
platforms. When
> > you're reading from DirectByteBuffer memory
> > (updateDirectByteBuffer), you're only using 32bit reads.
> I will add a comment in the code for this decision. The
reason is
> that read a long results in slightly worse performance in
this case,
> in updateBytes it is faster. I was able to get it to run
slightly
> faster by working directly with the address instead of
always adding
> address + off, but this makes things worse in the 32bit
case since
> all calculation will now be using long variables. So using
the getInt
> as in the current code feels like the best solution as it
strikes the
> best balance between 32 and 64bit. Below is how
updateByteBuffer
> looked with the rewrite I mentioned.
>
>
> ong address = ((DirectBuffer) buffer).address();
> crc = updateDirectByteBuffer(crc, address + pos, address
+ limit);
>
>
> private static int updateDirectByteBuffer(int crc,
long adr,
> long end) {
>
> // Do only byte reads for arrays so short they
can't be
> aligned if (end - adr >= 8) {
>
> // align on 8 bytes
> int alignLength = (8 - (int) (adr & 0x7)) & 0x7;
> for (long alignEnd = adr + alignLength; adr <
alignEnd;
> adr++) { crc = (crc >>> 8)
> ^ byteTable[(crc ^
UNSAFE.getByte(adr)) &
> 0xFF]; }
>
> if (ByteOrder.nativeOrder() ==
ByteOrder.BIG_ENDIAN) {
> crc = Integer.reverseBytes(crc);
> }
>
> // slicing-by-8
> for (; adr < (end - Long.BYTES); adr +=
Long.BYTES) {
> int firstHalf;
> int secondHalf;
> if (Unsafe.ADDRESS_SIZE == 4) {
> // On 32 bit platforms read two ints
instead of
> a single 64bit long firstHalf = UNSAFE.getInt(adr);
> secondHalf = UNSAFE.getInt(adr +
Integer.BYTES);
> } else {
> long value = UNSAFE.getLong(adr);
> if (ByteOrder.nativeOrder() ==
> ByteOrder.LITTLE_ENDIAN) { firstHalf = (int) value;
> secondHalf = (int) (value >>> 32);
> } else { // ByteOrder.BIG_ENDIAN
> firstHalf = (int) (value >>> 32);
> secondHalf = (int) value;
> }
> }
> crc ^= firstHalf;
> if (ByteOrder.nativeOrder() ==
> ByteOrder.LITTLE_ENDIAN) { crc = byteTable7[crc & 0xFF]
> ^ byteTable6[(crc >>> 8) & 0xFF]
> ^ byteTable5[(crc >>> 16) & 0xFF]
> ^ byteTable4[crc >>> 24]
> ^ byteTable3[secondHalf & 0xFF]
> ^ byteTable2[(secondHalf >>>
8) & 0xFF]
> ^ byteTable1[(secondHalf >>>
16) & 0xFF]
> ^ byteTable0[secondHalf >>> 24];
> } else { // ByteOrder.BIG_ENDIAN
> crc = byteTable0[secondHalf & 0xFF]
> ^ byteTable1[(secondHalf >>>
8) & 0xFF]
> ^ byteTable2[(secondHalf >>>
16) & 0xFF]
> ^ byteTable3[secondHalf >>> 24]
> ^ byteTable4[crc & 0xFF]
> ^ byteTable5[(crc >>> 8) & 0xFF]
> ^ byteTable6[(crc >>> 16) & 0xFF]
> ^ byteTable7[crc >>> 24];
> }
> }
>
> if (ByteOrder.nativeOrder() ==
ByteOrder.BIG_ENDIAN) {
> crc = Integer.reverseBytes(crc);
> }
> }
>
> // Tail
> for (; adr < end; adr++) {
> crc = (crc >>> 8)
> ^ byteTable[(crc ^
UNSAFE.getByte(adr)) & 0xFF];
> }
>
> return crc;
> }
>
>
> >
> > Also, in updateBytes, the usage of
> > Unsafe.ARRAY_INT_INDEX_SCALE/ARRAY_LONG_INDEX_SCALE to
index a byte
> > array sounds a little scary. To be ultra portable you
could check
> > that ARRAY_BYTE_INDEX_SCALE == 1 first and refuse to use
Unsafe for
> > byte arrays if it is not 1. Then use
Integer.BYTES/Long.BYTES to
> > manipulate 'offsets' instead. In updateDirectByteBuffer
it would be
> > more appropriate to use Integer.BYTES/Long.BYTES too.
> Good idea. Added a check in the initial if statement and it
will get
> automatically optimized away.
>
> > 225 firstHalf = (int) (value &
> > 0xFFFFFFFF); 226 secondHalf = (int) (value
> > >>> 32); 227 } else { // ByteOrder.BIG_ENDIAN
> > 228 firstHalf = (int) (value >>> 32);
> > 229 secondHalf = (int) (value &
> > 0xFFFFFFFF);
> >
> > firstHalf = (int) value; // this is equivalent for line 225
> > secondHalf = (int) value; // this is equivalent for line 229
> Done.
>
> Here is the latest webrev,
> http://cr.openjdk.java.net/~sfriberg/JDK-6321472/webrev.03
<http://cr.openjdk.java.net/%7Esfriberg/JDK-6321472/webrev.03>
>
> Cheers,
> Staffan
