concurrent
An object that may eventually be completed with a result value of type T which may be
awaited using blocking methods.
An object that may eventually be completed with a result value of type T which may be
awaited using blocking methods.
The Await object provides methods that allow accessing the result of an Awaitable
by blocking the current thread until the Awaitable has been completed or a timeout has
occurred.
A context to be notified by scala.concurrent.blocking when
a thread is about to block.
A context to be notified by scala.concurrent.blocking when
a thread is about to block. In effect this trait provides
the implementation for scala.concurrent.Await.
scala.concurrent.Await.result() and scala.concurrent.Await.ready()
locates an instance of BlockContext by first looking for one
provided through BlockContext.withBlockContext() and failing that,
checking whether Thread.currentThread is an instance of BlockContext.
So a thread pool can have its java.lang.Thread instances implement
BlockContext. There's a default BlockContext used if the thread
doesn't implement BlockContext.
Typically, you'll want to chain to the previous BlockContext,
like this:
val oldContext = BlockContext.current val myContext = new BlockContext { override def blockOn[T](thunk: =>T)(implicit permission: CanAwait): T = { // you'd have code here doing whatever you need to do // when the thread is about to block. // Then you'd chain to the previous context: oldContext.blockOn(thunk) } } BlockContext.withBlockContext(myContext) { // then this block runs with myContext as the handler // for scala.concurrent.blocking }
This marker trait is used by Await to ensure that Awaitable.ready and Awaitable.result are not directly called by user code.
This marker trait is used by Await to ensure that Awaitable.ready and Awaitable.result are not directly called by user code. An implicit instance of this trait is only available when user code is currently calling the methods on Await.
This class provides a simple FIFO queue of data objects, which are read by one or more reader threads.
This class provides a simple FIFO queue of data objects, which are read by one or more reader threads.
type of data exchanged
1.0, 10/03/2003
A DelayedLazyVal is a wrapper for lengthy computations which have a
valid partially computed result.
A DelayedLazyVal is a wrapper for lengthy computations which have a
valid partially computed result.
The first argument is a function for obtaining the result at any given
point in time, and the second is the lengthy computation. Once the
computation is complete, the apply method will stop recalculating it
and return a fixed value from that point forward.
2.8
An ExecutionContext can execute program logic asynchronously,
typically but not necessarily on a thread pool.
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.
It is possible to simply import
scala.concurrent.ExecutionContext.Implicits.global to obtain an
implicit ExecutionContext. This global context is a reasonable
default thread pool.
However, application developers should carefully consider where they
want to set 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 might want to avoid
hardcoding scala.concurrent.ExecutionContext.Implicits.global all
over the place in your code.
One approach is to add (implicit ec: ExecutionContext)
to methods which need an ExecutionContext. Then import a specific
context in one place for the entire application or module,
passing it implicitly to individual methods.
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.
An ExecutionContext that is also a Java Executor.
An ExecutionContext that is also a Java ExecutorService.
The trait that represents futures.
The trait that represents futures.
Asynchronous computations that yield futures are created with the Future.apply call:
val s = "Hello" val f: Future[String] = Future { s + " future!" } f onSuccess { case msg => println(msg) }
A marker indicating that a java.lang.Runnable provided to scala.concurrent.ExecutionContext
wraps a callback provided to Future.onComplete.
A marker indicating that a java.lang.Runnable provided to scala.concurrent.ExecutionContext
wraps a callback provided to Future.onComplete.
All callbacks provided to a Future end up going through onComplete, so this allows an
ExecutionContext to special-case callbacks that were executed by Future if desired.
Promise is an object which can be completed with a value or failed with an exception.
A SyncChannel allows one to exchange data synchronously between
a reader and a writer thread.
A SyncChannel allows one to exchange data synchronously between
a reader and a writer thread. The writer thread is blocked until the
data to be written has been read by a corresponding reader thread.
2.0, 04/17/2008
A class to provide safe concurrent access to a mutable cell.
A class to provide safe concurrent access to a mutable cell. All methods are synchronized.
type of the contained value
1.0, 10/03/2003
This class ...
This class ...
(Since version 2.11.2) Use java.util.concurrent.locks.Lock
1.0, 10/03/2003
Await is what is used to ensure proper handling of blocking for Awaitable instances.
Await is what is used to ensure proper handling of blocking for Awaitable instances.
While occasionally useful, e.g. for testing, it is recommended that you avoid Await when possible in favor of callbacks and combinators like onComplete and use in for comprehensions. Await will block the thread on which it runs, and could cause performance and deadlock issues.
Contains factory methods for creating execution contexts.
Future companion object.
The JavaConversions object provides implicit conversions supporting
interoperability between Scala and Java concurrency classes.
Used to designate a piece of code which potentially blocks, allowing the current BlockContext to adjust the runtime's behavior.
Used to designate a piece of code which potentially blocks, allowing the current BlockContext to adjust the runtime's behavior. Properly marking blocking code may improve performance or avoid deadlocks.
Blocking on an Awaitable should be done using Await.result instead of blocking.
A piece of code which contains potentially blocking or long running calls.
CancellationException if the computation was cancelled
InterruptedException in the case that a wait within the blocking body was interrupted
Starts an asynchronous computation and returns a Future object with the result of that computation.
Starts an asynchronous computation and returns a Future object with the result of that computation.
The result becomes available once the asynchronous computation is completed.
the type of the result
the asynchronous computation
the execution context on which the future is run
the Future holding the result of the computation
(Since version 2.11.0) Use Future { ... } instead.
Creates a promise object which can be completed with a value or an exception.
Creates a promise object which can be completed with a value or an exception.
the type of the value in the promise
the newly created Promise object
(Since version 2.11.0) Use Promise[T]() instead.
This package object contains primitives for concurrent and parallel programming.
Guide
A more detailed guide to Futures and Promises, including discussion and examples can be found at http://docs.scala-lang.org/overviews/core/futures.html.
Common Imports
When working with Futures, you will often find that importing the whole concurrent package is convenient, furthermore you are likely to need an implicit ExecutionContext in scope for many operations involving Futures and Promises:
Specifying Durations
Operations often require a duration to be specified. A duration DSL is available to make defining these easier:
Using Futures For Non-blocking Computation
Basic use of futures is easy with the factory method on Future, which executes a provided function asynchronously, handing you back a future result of that function without blocking the current thread. In order to create the Future you will need either an implicit or explicit ExecutionContext to be provided:
Avoid Blocking
Although blocking is possible in order to await results (with a mandatory timeout duration):
and although this is sometimes necessary to do, in particular for testing purposes, blocking in general is discouraged when working with Futures and concurrency in order to avoid potential deadlocks and improve performance. Instead, use callbacks or combinators to remain in the future domain: