ExecutionContext can execute program logic asynchronously,
typically but not necessarily on a thread pool.
A general purpose
ExecutionContext must be asynchronous in executing
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
APIs such as
Future.onComplete require you to provide a callback
and an implicit
ExecutionContext. The implicit
will be used to execute the callback.
While it is possible to simply import
scala.concurrent.ExecutionContext.Implicits.global to obtain an
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,
The recommended approach is to add
(implicit ec: ExecutionContext) to methods,
or class constructor parameters, which need an
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 may be appropriate to execute code
which blocks on IO or performs long-running computations.
are good ways to create a custom
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.
Prepares for the execution of a task. Returns the prepared
execution context. The recommended implementation of
prepare is to return
This method should no longer be overridden or called. It was
originally expected that
prepare would be called by
all libraries that consume ExecutionContexts, in order to
capture thread local context. However, this usage has proven
difficult to implement in practice and instead it is
now better to avoid using
Instead, if an
ExecutionContext needs to capture thread
local context, it should capture that context when it is
constructed, so that it doesn't need any additional