An ExecutionContext
can execute program logic asynchronously, typically but not necessarily on a thread pool.
A general purpose ExecutionContext
must be asynchronous in executing any Runnable
that is passed into its execute
-method. A special purpose ExecutionContext
may be synchronous but must only be passed to code that is explicitly safe to be run using a synchronously executing ExecutionContext
.
APIs such as Future.onComplete
require you to provide a callback and an implicit ExecutionContext
. The implicit ExecutionContext
will be used to execute the callback.
While it is possible to simply import scala.concurrent.ExecutionContext.Implicits.global
to obtain an implicit ExecutionContext
, application developers should carefully consider where they want to define the execution policy; ideally, one place per application — or per logically related section of code — will make a decision about which ExecutionContext
to use. That is, you will mostly want to avoid hardcoding, especially via an import, scala.concurrent.ExecutionContext.Implicits.global
. The recommended approach is to add (implicit ec: ExecutionContext)
to methods, or class constructor parameters, which need an ExecutionContext
.
Then locally import a specific ExecutionContext
in one place for the entire application or module, passing it implicitly to individual methods. Alternatively define a local implicit val with the required ExecutionContext
.
A custom ExecutionContext
may be appropriate to execute code which blocks on IO or performs long-running computations. ExecutionContext.fromExecutorService
and ExecutionContext.fromExecutor
are good ways to create a custom ExecutionContext
.
The intent of ExecutionContext
is to lexically scope code execution. That is, each method, class, file, package, or application determines how to run its own code. This avoids issues such as running application callbacks on a thread pool belonging to a networking library. The size of a networking library's thread pool can be safely configured, knowing that only that library's network operations will be affected. Application callback execution can be configured separately.
Attributes
- Companion
- object
- Source
- ExecutionContext.scala
- Graph
-
- Supertypes
- Known subtypes