object ExecutionContext
Contains factory methods for creating execution contexts.
- Source
- ExecutionContext.scala
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Value Members
- final def !=(arg0: Any): Boolean
Test two objects for inequality.
Test two objects for inequality.
- returns
true
if !(this == that), false otherwise.
- Definition Classes
- AnyRef → Any
- final def ##: Int
Equivalent to
x.hashCode
except for boxed numeric types andnull
.Equivalent to
x.hashCode
except for boxed numeric types andnull
. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. Fornull
returns a hashcode wherenull.hashCode
throws aNullPointerException
.- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
- final def ==(arg0: Any): Boolean
The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.- returns
true
if the receiver object is equivalent to the argument;false
otherwise.
- Definition Classes
- AnyRef → Any
- final def asInstanceOf[T0]: T0
Cast the receiver object to be of type
T0
.Cast the receiver object to be of type
T0
.Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression
1.asInstanceOf[String]
will throw aClassCastException
at runtime, while the expressionList(1).asInstanceOf[List[String]]
will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.- returns
the receiver object.
- Definition Classes
- Any
- Exceptions thrown
ClassCastException
if the receiver object is not an instance of the erasure of typeT0
.
- def clone(): AnyRef
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the
clone
method is platform dependent.- returns
a copy of the receiver object.
- final val defaultReporter: (Throwable) => Unit
The default reporter simply prints the stack trace of the
Throwable
to System.err.The default reporter simply prints the stack trace of the
Throwable
to System.err.- returns
the function for error reporting
- final def eq(arg0: AnyRef): Boolean
Tests whether the argument (
that
) is a reference to the receiver object (this
).Tests whether the argument (
that
) is a reference to the receiver object (this
).The
eq
method implements an equivalence relation on non-null instances ofAnyRef
, and has three additional properties:- It is consistent: for any non-null instances
x
andy
of typeAnyRef
, multiple invocations ofx.eq(y)
consistently returnstrue
or consistently returnsfalse
. - For any non-null instance
x
of typeAnyRef
,x.eq(null)
andnull.eq(x)
returnsfalse
. null.eq(null)
returnstrue
.
When overriding the
equals
orhashCode
methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2
), they should be equal to each other (o1 == o2
) and they should hash to the same value (o1.hashCode == o2.hashCode
).- returns
true
if the argument is a reference to the receiver object;false
otherwise.
- Definition Classes
- AnyRef
- It is consistent: for any non-null instances
- def equals(arg0: AnyRef): Boolean
The equality method for reference types.
- def finalize(): Unit
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the
finalize
method is invoked, as well as the interaction betweenfinalize
and non-local returns and exceptions, are all platform dependent.- Attributes
- protected[lang]
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.Throwable])
- Note
not specified by SLS as a member of AnyRef
- def fromExecutor(e: Executor): ExecutionContextExecutor
Creates an
ExecutionContext
from the givenExecutor
with the default reporter.Creates an
ExecutionContext
from the givenExecutor
with the default reporter.- e
the
Executor
to use. Ifnull
, a newExecutor
is created with default configuration.- returns
the
ExecutionContext
using the givenExecutor
- def fromExecutor(e: Executor, reporter: (Throwable) => Unit): ExecutionContextExecutor
Creates an
ExecutionContext
from the givenExecutor
.Creates an
ExecutionContext
from the givenExecutor
.- e
the
Executor
to use. Ifnull
, a newExecutor
is created with default configuration.- reporter
a function for error reporting
- returns
the
ExecutionContext
using the givenExecutor
- def fromExecutorService(e: ExecutorService): ExecutionContextExecutorService
Creates an
ExecutionContext
from the givenExecutorService
with the default reporter.Creates an
ExecutionContext
from the givenExecutorService
with the default reporter.If it is guaranteed that none of the executed tasks are blocking, a single-threaded
ExecutorService
can be used to create anExecutionContext
as follows:import java.util.concurrent.Executors val ec = ExecutionContext.fromExecutorService(Executors.newSingleThreadExecutor())
- e
the
ExecutorService
to use. Ifnull
, a newExecutorService
is created with default configuration.- returns
the
ExecutionContext
using the givenExecutorService
- def fromExecutorService(e: ExecutorService, reporter: (Throwable) => Unit): ExecutionContextExecutorService
Creates an
ExecutionContext
from the givenExecutorService
.Creates an
ExecutionContext
from the givenExecutorService
.- e
the
ExecutorService
to use. Ifnull
, a newExecutorService
is created with default configuration.- reporter
a function for error reporting
- returns
the
ExecutionContext
using the givenExecutorService
- final def getClass(): Class[_ <: AnyRef]
Returns the runtime class representation of the object.
- final lazy val global: ExecutionContextExecutor
The global ExecutionContext.
The global ExecutionContext. This default
ExecutionContext
implementation is backed by a work-stealing thread pool. It can be configured via the following system properties:scala.concurrent.context.minThreads
= defaults to "1"scala.concurrent.context.numThreads
= defaults to "x1" (i.e. the current number of available processors * 1)scala.concurrent.context.maxThreads
= defaults to "x1" (i.e. the current number of available processors * 1)scala.concurrent.context.maxExtraThreads
= defaults to "256"
The pool size of threads is then
numThreads
bounded byminThreads
on the lower end andmaxThreads
on the high end.The
maxExtraThreads
is the maximum number of extra threads to have at any given time to evade deadlock, see scala.concurrent.blocking.The
global
execution context can be used explicitly, by defining animplicit val ec: scala.concurrent.ExecutionContext = scala.concurrent.ExecutionContext.global
, or by importing ExecutionContext.Implicits.global.Batching short-lived nested tasks
Asynchronous code with short-lived nested tasks is executed more efficiently when using
ExecutionContext.opportunistic
(continue reading to learn why it isprivate[scala]
and how to access it).ExecutionContext.opportunistic
uses the same thread pool asExecutionContext.global
. It attempts to batch nested task and execute them on the same thread as the enclosing task. This is ideally suited to execute short-lived tasks as it reduces the overhead of context switching.WARNING: long-running and/or blocking tasks should be demarcated within scala.concurrent.blocking-blocks to ensure that any pending tasks in the current batch can be executed by another thread on
global
.How to use
This field is
private[scala]
to maintain binary compatibility. It was added in 2.13.4, code that references it directly fails to run with a 2.13.0-3 Scala library.Libraries should not reference this field directly because users of the library might be using an earlier Scala version. In order to use the batching
ExecutionContext
in a library, the code needs to fall back toglobal
in case theopportunistic
field is missing (example below). The resultingExecutionContext
has batching behavior in all Scala 2.13 versions (global
is batching in 2.13.0-3).implicit val ec: scala.concurrent.ExecutionContext = try { scala.concurrent.ExecutionContext.getClass .getDeclaredMethod("opportunistic") .invoke(scala.concurrent.ExecutionContext) .asInstanceOf[scala.concurrent.ExecutionContext] } catch { case _: NoSuchMethodException => scala.concurrent.ExecutionContext.global }
Application authors can safely use the field because the Scala version at run time is the same as at compile time. Options to bypass the access restriction include:
- Using a structural type (example below). This uses reflection at run time.
- Writing a Scala
object
in thescala
package (example below). - Writing a Java source file. This works because
private[scala]
is emitted aspublic
in Java bytecode.
// Option 1 implicit val ec: scala.concurrent.ExecutionContext = (scala.concurrent.ExecutionContext: {def opportunistic: scala.concurrent.ExecutionContextExecutor} ).opportunistic // Option 2 package scala { object OpportunisticEC { implicit val ec: scala.concurrent.ExecutionContext = scala.concurrent.ExecutionContext.opportunistic } }
- returns
the global ExecutionContext
- def hashCode(): Int
The hashCode method for reference types.
- final def isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object has the same erasure as
T0
.Test whether the dynamic type of the receiver object has the same erasure as
T0
.Depending on what
T0
is, the test is done in one of the below ways:T0
is a non-parameterized class type, e.g.BigDecimal
: this method returnstrue
if the value of the receiver object is aBigDecimal
or a subtype ofBigDecimal
.T0
is a parameterized class type, e.g.List[Int]
: this method returnstrue
if the value of the receiver object is someList[X]
for anyX
. For example,List(1, 2, 3).isInstanceOf[List[String]]
will return true.T0
is some singleton typex.type
or literalx
: this method returnsthis.eq(x)
. For example,x.isInstanceOf[1]
is equivalent tox.eq(1)
T0
is an intersectionX with Y
orX & Y: this method is equivalent to
x.isInstanceOf[X] && x.isInstanceOf[Y]T0
is a unionX | Y
: this method is equivalent tox.isInstanceOf[X] || x.isInstanceOf[Y]
T0
is a type parameter or an abstract type member: this method is equivalent toisInstanceOf[U]
whereU
isT0
's upper bound,Any
ifT0
is unbounded. For example,x.isInstanceOf[A]
whereA
is an unbounded type parameter will return true for any value ofx
.
This is exactly equivalent to the type pattern
_: T0
- returns
true
if the receiver object is an instance of erasure of typeT0
;false
otherwise.
- Definition Classes
- Any
- Note
due to the unexpectedness of
List(1, 2, 3).isInstanceOf[List[String]]
returning true andx.isInstanceOf[A]
whereA
is a type parameter or abstract member returning true, these forms issue a warning.
- final def ne(arg0: AnyRef): Boolean
Equivalent to
!(this eq that)
.Equivalent to
!(this eq that)
.- returns
true
if the argument is not a reference to the receiver object;false
otherwise.
- Definition Classes
- AnyRef
- final def notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
- final def notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
- final def synchronized[T0](arg0: => T0): T0
Executes the code in
body
with an exclusive lock onthis
.Executes the code in
body
with an exclusive lock onthis
.- returns
the result of
body
- Definition Classes
- AnyRef
- def toString(): String
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
- returns
a String representation of the object.
- Definition Classes
- AnyRef → Any
- final def wait(): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- Note
not specified by SLS as a member of AnyRef
- final def wait(arg0: Long, arg1: Int): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- Note
not specified by SLS as a member of AnyRef
- final def wait(arg0: Long): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
- object Implicits
- object parasitic extends ExecutionContextExecutor with BatchingExecutor
WARNING: Only ever execute logic which will quickly return control to the caller.
WARNING: Only ever execute logic which will quickly return control to the caller.
This
ExecutionContext
steals execution time from other threads by having itsRunnable
s run on theThread
which callsexecute
and then yielding back control to the caller after *all* itsRunnable
s have been executed. Nested invocations ofexecute
will be trampolined to prevent uncontrolled stack space growth.When using
parasitic
with abstractions such asFuture
it will in many cases be non-deterministic as to whichThread
will be executing the logic, as it depends on when/if thatFuture
is completed.Do *not* call any blocking code in the
Runnable
s submitted to thisExecutionContext
as it will prevent progress by other enqueuedRunnable
s and the callingThread
.Symptoms of misuse of this
ExecutionContext
include, but are not limited to, deadlocks and severe performance problems.Any
NonFatal
orInterruptedException
s will be reported to thedefaultReporter
.
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int
,Float
,Array
orOption
which are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collection
and its sub-packages contain Scala's collections frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.sys
- Interaction with other processes and the operating systemscala.util.matching
- Regular expressionsOther packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
scala.reflect
- Scala's reflection API (scala-reflect.jar)scala.xml
- XML parsing, manipulation, and serialization (scala-xml.jar)scala.collection.parallel
- Parallel collections (scala-parallel-collections.jar)scala.util.parsing
- Parser combinators (scala-parser-combinators.jar)scala.swing
- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)Automatic imports
Identifiers in the scala package and the
scala.Predef
object are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
List
is an alias forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.