BELUGA BEHR created HBASE-20211: ----------------------------------- Summary: ReadOnlyBufferException In UnsafeAccess Key: HBASE-20211 URL: https://issues.apache.org/jira/browse/HBASE-20211 Project: HBase Issue Type: Bug Components: hbase Affects Versions: 2.0.0 Reporter: BELUGA BEHR
If you trace the BBUtils API, what you see is this code: {code:java} public static void copyFromBufferToArray(byte[] out, ByteBuffer in, int sourceOffset, int destinationOffset, int length) { if (in.hasArray()) { System.arraycopy(in.array(), sourceOffset + in.arrayOffset(), out, destinationOffset, length); } else if (UNSAFE_AVAIL) { UnsafeAccess.copy(in, sourceOffset, out, destinationOffset, length); } else { ByteBuffer inDup = in.duplicate(); inDup.position(sourceOffset); inDup.get(out, destinationOffset, length); } } {code} A ByteBuffer is being used here, which is not read-only, so it actually hits on the first condition and executes this code: {quote}System.arraycopy(in.array(), sourceOffset + in.arrayOffset(), out, destinationOffset, length); {quote} Which is almost exactly what the {{ByteBuffer}} relative bulk get method does anyway, so there is no savings here, just overheard and complexity. In regards to the second condition... there is a bug there that I just noticed. {code:java|title=org.apache.hadoop.hbase.util.UnsafeAccess} public static void copy(ByteBuffer src, int srcOffset, byte[] dest, int destOffset, int length) { long srcAddress = srcOffset; Object srcBase = null; if (src.isDirect()) { srcAddress = srcAddress + ((DirectBuffer) src).address(); } else { srcAddress = srcAddress + BYTE_ARRAY_BASE_OFFSET + src.arrayOffset(); srcBase = src.array(); } long destAddress = destOffset + BYTE_ARRAY_BASE_OFFSET; unsafeCopy(srcBase, srcAddress, dest, destAddress, length); } {code} This issue here is the [arrayOffset()|https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html#arrayOffset--] call. The JavaDocs here say: {quote}Invoke the hasArray method before invoking this method in order to ensure that this buffer has an accessible backing array. {quote} However, as we saw in the previous method, if _hasArray_ returns true, we do _System.arraycopy,_ so the only reason we would be in this _copy_ code is if there was no access to the backing array, yet here it is, depending on it having such access. That could cause problems with Read-Only ByteBuffers that does not affect the _relative bulk get method_. {code:java} public class Test { public static void main(String[] args) throws IOException { ByteArrayOutputStream baos = new ByteArrayOutputStream(); ByteBufferWriterOutputStream bbwos = new ByteBufferWriterOutputStream(baos); ByteBuffer bbSmall = ByteBuffer.wrap(new byte[512]).asReadOnlyBuffer(); bbwos.write(bbSmall, 0, 512); bbwos.close(); } } Exception in thread "main" java.nio.ReadOnlyBufferException at java.nio.ByteBuffer.arrayOffset(ByteBuffer.java:1024) at org.apache.hadoop.hbase.util.UnsafeAccess.copy(UnsafeAccess.java:398) at org.apache.hadoop.hbase.util.ByteBufferUtils.copyFromBufferToArray(ByteBufferUtils.java:54) at org.apache.hadoop.hbase.io.ByteBufferWriterOutputStream.write(ByteBufferWriterOutputStream.java:59) at org.apache.hadoop.hbase.io.Test.main(Test.java:14) {code} -- This message was sent by Atlassian JIRA (v7.6.3#76005)