Is this bloom filter threadsafe?

[LeifW]

That is, is calling .add and .mightContain concurrently from many different threads going to work?

[harpocrates]

I wrote a short program to try to find incorrect behavior in the presence of multiple threads, and it unfortunately appears to find some. I think that counts as a witness proof that the bloom filter is not thread-safe.

Looking at the implementation: the backing array would need to use atomic operations like getAndBitWiseOr or else do some locking, but it does neither. It looks like the Java 9 VarHandle API would make this all very possible and efficient using ByteBuffer's, but I've got no idea how to do that without dropping Java 8 support.

bloom-filter-scala/bloom-filter/src/main/scala/bloomfilter/mutable/UnsafeBitArray.scala

Lines 19 to 26 in b2c41c0

	def set(index: Long): Unit = {
	val offset = ptr + (index >>> 6) * 8L
	val long = unsafe.getLong(offset)
	if ((long & (1L << index)) == 0) {
	unsafe.putLong(offset, long | (1L << index))
	bitCount += 1
	}
	}

[rac021]

Will there be a thread-safe implementation of this Bloom filter ?