package io.github.timwspence.cats.stm
import java.util.concurrent.atomic.AtomicReference
import io.github.timwspence.cats.stm.STM.internal._
/**
* Transactional variable - a mutable memory location
* that can be read or written to via `STM` actions.
*
* Analagous to `cats.effect.concurrent.Ref`.
*/
final class TVar[A] private[stm] (
private[stm] val id: Long,
@volatile private[stm] var value: A,
private[stm] val pending: AtomicReference[Map[TxId, Txn]]
) {
/**
* Get the current value as an
* `STM` action.
*/
def get: STM[A] = STM { log =>
val entry = getOrInsert(log)
TSuccess(entry.unsafeGet[A])
}
/**
* Set the current value as an
* `STM` action.
*/
def set(a: A): STM[Unit] = STM { log =>
val entry = getOrInsert(log)
TSuccess(entry.unsafeSet(a))
}
/**
* Modify the current value as an
* `STM` action.
*/
def modify(f: A => A): STM[Unit] = STM { log =>
val entry = getOrInsert(log)
val updated = f(entry.unsafeGet[A])
TSuccess(entry.unsafeSet(updated))
}
private def getOrInsert(log: TLog): TLogEntry =
if (log.contains(id))
log(id)
else {
val entry = TLogEntry(this, value)
log += id -> entry
entry
}
}
object TVar {
def of[A](value: A): STM[TVar[A]] = STM { _ =>
val id = IdGen.incrementAndGet
TSuccess(new TVar(id, value, new AtomicReference(Map())))
}
}
