Immutable collection (an example in book of scala in depth)

Question

In the book, it has the following example, it only sync the insert, but didn't sync lookup.I knew the currentIndex will point to a different object after insert, but is the operation of pointing to a different object atomic? example, suppose the pointer is of 8 bytes (on 64 bit machine), then at some point currentIndex will switch the pointer, but if that switch is not atomic, such as it first switch the first 4 bytes, and then switch the second 4 bytes, and if between the first and second switch, we lookup the data, then the pointer points to an object never exists and that will cause problem

class ImmutableService[Key, Value] extends Service[Key, Value] {
   var currentIndex = new ImmutableHashMap[Key,Value]
   def lookUp(k: Key): Option[Value] = currentIndex.get(k)
   def insert(k: Key, v: Value): Unit = synchronized {
       currentIndex = currentIndex + ((k, v))
   }
}

From http://stackoverflow.com/questions/4756536/what-operations-in-java-are-consider-atomic ,and elsewhere, all assignments are considered atomic. — Chick, May 14 '13 at 03:44

score 0 · Answer 1 · edited May 23 '17 at 12:30

0

Yes, currentIndex is a reference - so changes to it will be done atomically.

Check:

Are 64 bit assignments in Java atomic on a 32 bit machine?

edited May 23 '17 at 12:30

Community

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answered Jun 07 '13 at 23:59

Sandipan

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Immutable collection (an example in book of scala in depth)

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