final class TaskLocal[A] extends AnyRef
A TaskLocal is like a
ThreadLocal
that is pure and with a flexible scope, being processed in the
context of the Task data type.
This data type wraps monix.execution.misc.Local.
Just like a ThreadLocal, usage of a TaskLocal is safe,
the state of all current locals being transported over
async boundaries (aka when threads get forked) by the Task
run-loop implementation, but only when the Task reference
gets executed with Task.Options.localContextPropagation
set to true.
One way to achieve this is with Task.executeWithOptions,
a single call is sufficient just before runAsync:
import monix.execution.Scheduler.Implicits.global val t = Task(42) t.executeWithOptions(_.enableLocalContextPropagation) // triggers the actual execution .runToFuture
Another possibility is to use Task.runToFutureOpt or
Task.runToFutureOpt instead of runAsync and specify the set of
options implicitly:
{
implicit val options = Task.defaultOptions.enableLocalContextPropagation
// Options passed implicitly
val f = t.runToFutureOpt
}Full example:
import monix.eval.{Task, TaskLocal} val task: Task[Unit] = for { local <- TaskLocal(0) value1 <- local.read // value1 == 0 _ <- local.write(100) value2 <- local.read // value2 == 100 value3 <- local.bind(200)(local.read.map(_ * 2)) // value3 == 200 * 2 value4 <- local.read // value4 == 100 _ <- local.clear value5 <- local.read // value5 == 0 } yield { // Should print 0, 100, 400, 100, 0 println("value1: " + value1) println("value2: " + value2) println("value3: " + value3) println("value4: " + value4) println("value5: " + value5) } // For transporting locals over async boundaries defined by // Task, any Scheduler will do, however for transporting locals // over async boundaries managed by Future and others, you need // a `TracingScheduler` here: import monix.execution.Scheduler.Implicits.global // Needs enabling the "localContextPropagation" option // just before execution implicit val opts = Task.defaultOptions.enableLocalContextPropagation // Triggering actual execution val result = task.runToFutureOpt
- Source
- TaskLocal.scala
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- def bind[R](value: A)(task: Task[R]): Task[R]
Binds the local var to a
valuefor the duration of the giventaskexecution.Binds the local var to a
valuefor the duration of the giventaskexecution.// Should yield 200 on execution, regardless of what value // we have in `local` at the time of evaluation val task: Task[Int] = for { local <- TaskLocal(0) value <- local.bind(100)(local.read.map(_ * 2)) } yield value
- value
is the value to be set in this local var when the task evaluation is triggered (aka lazily)
- task
is the Task to wrap, having the given
valueas the response to read queries and transported over asynchronous boundaries — on finish the local gets reset to the previous value
- See also
bindL for the version with a lazy
value.
- def bindClear[R](task: Task[R]): Task[R]
Clears the local var to the default for the duration of the given
taskexecution.Clears the local var to the default for the duration of the given
taskexecution.// Should yield 0 on execution, regardless of what value // we have in `local` at the time of evaluation val task: Task[Int] = for { local <- TaskLocal(0) value <- local.bindClear(local.read.map(_ * 2)) } yield value
- def bindL[R](value: Task[A])(task: Task[R]): Task[R]
Binds the local var to a
valuefor the duration of the giventaskexecution, thevalueitself being lazily evaluated in the Task context.Binds the local var to a
valuefor the duration of the giventaskexecution, thevalueitself being lazily evaluated in the Task context.// Should yield 200 on execution, regardless of what value // we have in `local` at the time of evaluation val task: Task[Int] = for { local <- TaskLocal(0) value <- local.bindL(Task.eval(100))(local.read.map(_ * 2)) } yield value
- value
is the value to be set in this local var when the task evaluation is triggered (aka lazily)
- task
is the Task to wrap, having the given
valueas the response to read queries and transported over asynchronous boundaries — on finish the local gets reset to the previous value
- See also
bind for the version with a strict
value.
- def clear: Task[Unit]
Clears the local value, making it return its
default. - def clone(): AnyRef
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- def local: Task[Local[A]]
Returns monix.execution.misc.Local instance used in this TaskLocal.
Returns monix.execution.misc.Local instance used in this TaskLocal.
Note that
TaskLocal.bindwill restore the original local value on the thread where theTask'srun-loop ends up so it might lead to leaving local modified in other thread. - final def ne(arg0: AnyRef): Boolean
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- def read: Task[A]
Returns the current local value (in the
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- def write(value: A): Task[Unit]
Updates the local value.
This is the API documentation for the Monix library.
Package Overview
monix.execution exposes lower level primitives for dealing with asynchronous execution:
Atomictypes, as alternative tojava.util.concurrent.atomicmonix.catnap exposes pure abstractions built on top of the Cats-Effect type classes:
monix.eval is for dealing with evaluation of results, thus exposing Task and Coeval.
monix.reactive exposes the
Observablepattern:Observableimplementationsmonix.tail exposes Iterant for purely functional pull based streaming:
BatchandBatchCursor, the alternatives to Scala'sIterableandIteratorrespectively that we are using within Iterant's encodingYou can control evaluation with type you choose - be it Task, Coeval, cats.effect.IO or your own as long as you provide correct cats-effect or cats typeclass instance.