In the document "Effective Scala" published by twitter, I see a code example:
class Pool(conns: Seq[Conn]) {
private[this] val waiters = new Broker[Conn]
private[this] val returnConn = new Broker[Conn]
val get: Offer[Conn] = waiters.recv
def put(c: Conn) { returnConn ! c }
private[this] def loop(connq: Queue[Conn]) {
Offer.choose(
if (connq.isEmpty) Offer.never else {
val (head, rest) = connq.dequeue
waiters.send(head) { _ => loop(rest) }
},
returnConn.recv { c => loop(connq enqueue c) }
).sync()
}
loop(Queue.empty ++ conns)
}
The code doesn't appear to be tail recursive, and isn't annotated as such. Since this is a connection pool that would presumably be left running for the life of the program, what would prevent a pool like this from eventually blowing up the stack, and generating a StackOverflowException?
The code is not recursive at all! loop
does not call itself. It passes closures { _ => loop(rest) }
and { c => loop(connq enqueue c) }
to waiters.send
and returnConn.recv
respectively which call loop
again. No recursion hence no stack overflow.