Hi,Using unsafe to read fields will make the code very brittle and require us to further detect and buffer types and which fields to read and handle. Currently this seems to be a rather uncommon case, as the code in Adler32 and CRC32 has done a full allocation in JDK 8, and by far either wrapped ByteBuffers or DirectByteBuffers are expected to be used. So for now I will keep the code as is without further complications.
The performance with the copying looks reasonable. The result is multiplied with array length (@OperationsPerInvocation(65536 or 1024)) so score ends up being bytes/ms.
64k buffer lengthBenchmark Mode Samples Score Score error Units o.c.CRC32C.directByteBuffer_64K thrpt 5 998151.406 1539.451 ops/ms o.c.CRC32C.readonlyByteBuffer_64K thrpt 5 961665.219 36823.059 ops/ms o.c.CRC32C.wrappedByteBuffer_64K thrpt 5 1030445.833 9069.889 ops/ms
1k buffer lengthBenchmark Mode Samples Score Score error Units o.c.CRC32C.directByteBuffer_1K thrpt 5 987614.289 3506.829 ops/ms o.c.CRC32C.readonlyByteBuffer_1K thrpt 5 691888.488 217080.205 ops/ms o.c.CRC32C.wrappedByteBuffer_1K thrpt 5 974676.434 463.487 ops/ms
//Staffan On 10/23/2014 02:05 AM, Peter Levart wrote:
On 10/23/2014 10:16 AM, Stanimir Simeonoff wrote:Unsafe is available, so the fields (array, offset) can be read directlyUNSAFE.getObject(buffer, hbOffset), UNSAFE.getObject(buffer, offsetOffset).No need for MethodHandlers.During class init the offsets have to be resolved, pretty much like any CASutilizing algorithm.I didn't propose it as readOnlyBuffers are very, very rarely used and evenmore 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...PeterStanimir 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.07Hi 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 itperform faster if a redundant copy is avoided. Ah, you already told us thatyou 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 withdoPrivileged() 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 patchand 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 sizeof 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 twoints > > 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 usingthe 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 useUnsafe 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 itwill 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
