evalOnExecutor

core/shared/src/main/scala/cats/effect/IO.scala

@@ -359,11 +359,38 @@ sealed abstract class IO[+A] private () extends IOPlatform[A] {
    */
   def evalOn(ec: ExecutionContext): IO[A] = IO.EvalOn(this, ec)
 
+  /**
+   * Shifts the execution of the current IO to the specified [[java.util.concurrent.Executor]].
+   *
+   * @param executor
+   * @return
+   */
+  def evalOnExecutor(executor: Executor): IO[A] = {
+    require(executor != null, "Cannot pass undefined Executor as an argument")
+    executor match {
+      case ec: ExecutionContext =>
+        evalOn(ec: ExecutionContext)
+      case executor =>
+        IO.executionContext.flatMap { refEc =>
+          val newEc: ExecutionContext =
+            ExecutionContext.fromExecutor(executor, refEc.reportFailure)
+          evalOn(newEc)
+        }
+    }
+  }
+
   def startOn(ec: ExecutionContext): IO[FiberIO[A @uncheckedVariance]] = start.evalOn(ec)
 
+  def startOnExecutor(executor: Executor): IO[FiberIO[A @uncheckedVariance]] =
+    start.evalOnExecutor(executor)
+
   def backgroundOn(ec: ExecutionContext): ResourceIO[IO[OutcomeIO[A @uncheckedVariance]]] =
     Resource.make(startOn(ec))(_.cancel).map(_.join)
 
+  def backgroundOnExecutor(
+      executor: Executor): ResourceIO[IO[OutcomeIO[A @uncheckedVariance]]] =
+    Resource.make(startOnExecutor(executor))(_.cancel).map(_.join)
+
   /**
    * Given an effect which might be [[uncancelable]] and a finalizer, produce an effect which
    * can be canceled by running the finalizer. This combinator is useful for handling scenarios

kernel/shared/src/main/scala/cats/effect/kernel/Async.scala

@@ -166,6 +166,23 @@ trait Async[F[_]] extends AsyncPlatform[F] with Sync[F] with Temporal[F] {
    */
   def evalOn[A](fa: F[A], ec: ExecutionContext): F[A]
 
+  /**
+   * [[Async.evalOn]] with provided [[java.util.concurrent.Executor]]
+   */
+  def evalOnExecutor[A](fa: F[A], executor: Executor): F[A] = {
+    require(executor != null, "Cannot pass undefined Executor as an argument")
+    executor match {
+      case ec: ExecutionContext =>
+        evalOn[A](fa, ec: ExecutionContext)
+      case executor =>
+        flatMap(executionContext) { refEc =>
+          val newEc: ExecutionContext =
+            ExecutionContext.fromExecutor(executor, refEc.reportFailure)
+          evalOn[A](fa, newEc)
+        }
+    }
+  }
+
   /**
    * [[Async.evalOn]] as a natural transformation.
    */
@@ -174,6 +191,14 @@ trait Async[F[_]] extends AsyncPlatform[F] with Sync[F] with Temporal[F] {
       def apply[A](fa: F[A]): F[A] = evalOn(fa, ec)
     }
 
+  /**
+   * [[Async.evalOnExecutor]] as a natural transformation.
+   */
+  def evalOnExecutorK(executor: Executor): F ~> F =
+    new (F ~> F) {
+      def apply[A](fa: F[A]): F[A] = evalOnExecutor(fa, executor)
+    }
+
   /**
    * Start a new fiber on a different execution context.
    *
@@ -182,6 +207,14 @@ trait Async[F[_]] extends AsyncPlatform[F] with Sync[F] with Temporal[F] {
   def startOn[A](fa: F[A], ec: ExecutionContext): F[Fiber[F, Throwable, A]] =
     evalOn(start(fa), ec)
 
+  /**
+   * Start a new fiber on a different executor.
+   *
+   * See [[GenSpawn.start]] for more details.
+   */
+  def startOnExecutor[A](fa: F[A], executor: Executor): F[Fiber[F, Throwable, A]] =
+    evalOnExecutor(start(fa), executor)
+
   /**
    * Start a new background fiber on a different execution context.
    *
@@ -192,6 +225,16 @@ trait Async[F[_]] extends AsyncPlatform[F] with Sync[F] with Temporal[F] {
       ec: ExecutionContext): Resource[F, F[Outcome[F, Throwable, A]]] =
     Resource.make(startOn(fa, ec))(_.cancel)(this).map(_.join)
 
+  /**
+   * Start a new background fiber on a different executor.
+   *
+   * See [[GenSpawn.background]] for more details.
+   */
+  def backgroundOnExecutor[A](
+      fa: F[A],
+      executor: Executor): Resource[F, F[Outcome[F, Throwable, A]]] =
+    Resource.make(startOnExecutor(fa, executor))(_.cancel)(this).map(_.join)
+
   /**
    * Obtain a reference to the current execution context.
    */

kernel/shared/src/main/scala/cats/effect/kernel/syntax/AsyncSyntax.scala

@@ -16,8 +16,9 @@
 
 package cats.effect.kernel.syntax
 
-import cats.effect.kernel.{Async, Fiber, Outcome, Resource, Sync}
+import cats.effect.kernel._
 
+import java.util.concurrent.Executor
 import scala.concurrent.ExecutionContext
 
 trait AsyncSyntax {
@@ -30,13 +31,23 @@ final class AsyncOps[F[_], A] private[syntax] (private[syntax] val wrapped: F[A]
   def evalOn(ec: ExecutionContext)(implicit F: Async[F]): F[A] =
     Async[F].evalOn(wrapped, ec)
 
+  def evalOnExecutor(executor: Executor)(implicit F: Async[F]): F[A] =
+    Async[F].evalOnExecutor(wrapped, executor)
+
   def startOn(ec: ExecutionContext)(implicit F: Async[F]): F[Fiber[F, Throwable, A]] =
     Async[F].startOn(wrapped, ec)
 
+  def startOnExecutor(executor: Executor)(implicit F: Async[F]): F[Fiber[F, Throwable, A]] =
+    Async[F].startOnExecutor(wrapped, executor)
+
   def backgroundOn(ec: ExecutionContext)(
       implicit F: Async[F]): Resource[F, F[Outcome[F, Throwable, A]]] =
     Async[F].backgroundOn(wrapped, ec)
 
+  def backgroundOnExecutor(executor: Executor)(
+      implicit F: Async[F]): Resource[F, F[Outcome[F, Throwable, A]]] =
+    Async[F].backgroundOnExecutor(wrapped, executor)
+
   def syncStep[G[_]: Sync](limit: Int)(implicit F: Async[F]): G[Either[F[A], A]] =
     Async[F].syncStep[G, A](wrapped, limit)
 }