TMVar
A convenience implementation in the Txn
monad, built on top of TVar
.
You can think of this as a mutable memory location that may contain a value. Writes will block if full and reads will block if empty.
import cats.effect.IO
import cats.effect.unsafe.implicits.global
import cats.syntax.semigroup._
import cats.instances.string._
import io.github.timwspence.cats.stm.STM
val stm = STM.runtime[IO].unsafeRunSync()
// stm: STM[IO] = io.github.timwspence.cats.stm.STM$Make$$anon$1$$anon$2@225656db
import stm._
val txn: Txn[String] = for {
tmvar <- TMVar.empty[String]
_ <- tmvar.put("Hello") //Would block if full
hello <- tmvar.take //Would block if empty
_ <- tmvar.put("world") //Would block if full
world <- tmvar.read //Would block if empty.
} yield hello |+| world
// txn: Txn[String] = Bind(
// txn = Bind(
// txn = Alloc(
// v = Delay(
// thunk = cats.effect.IO$$$Lambda$10319/0x0000000802cce040@f589e2e,
// event = cats.effect.tracing.TracingEvent$StackTrace
// )
// ),
// f = scala.Function1$$Lambda$10388/0x0000000802d97040@3bd057e9
// ),
// f = <function1>
// )
val result = stm.commit(txn).unsafeRunSync()
// result: String = "Helloworld"