Spawn: Difference between revisions

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== Usage ==
== Usage ==


Spawn is used to run background tasks, for example for monitoring or handling incoming requests. Since the thread number is returned, <source lang=apl inline>⎕TSYNC</syntaxhighlight> ("Thread Synchronise") is provided to retrieve the result, given the thread number. If the result is ready before <source lang=apl inline>⎕TSYNC</syntaxhighlight> is used, it prints to the [[session]] if applicable.
Spawn is used to run background tasks, for example for monitoring or handling incoming requests. Since the thread number is returned, <syntaxhighlight lang=apl inline>⎕TSYNC</syntaxhighlight> ("Thread Synchronise") is provided to retrieve the result, given the thread number. If the result is ready before <syntaxhighlight lang=apl inline>⎕TSYNC</syntaxhighlight> is used, it prints to the [[session]] if applicable.


Spawn is often used in conjunction with the [[Each]] operator (<source lang=apl inline>¨</syntaxhighlight>) to launch multiple threads in parallel.
Spawn is often used in conjunction with the [[Each]] operator (<syntaxhighlight lang=apl inline>¨</syntaxhighlight>) to launch multiple threads in parallel.


As Spawn is an operator, it cannot be directly used with a [[niladic function]], since a niladic function is called immediately when its name is referenced. As a workaround, the niladic function can be wrapped in a [[dfn]] and called with a dummy argument: <source lang=apl inline>{nilFun}&⍬</syntaxhighlight>
As Spawn is an operator, it cannot be directly used with a [[niladic function]], since a niladic function is called immediately when its name is referenced. As a workaround, the niladic function can be wrapped in a [[dfn]] and called with a dummy argument: <syntaxhighlight lang=apl inline>{nilFun}&⍬</syntaxhighlight>


== Examples ==
== Examples ==
<source lang=apl>
<syntaxhighlight lang=apl>
       ÷&4        ⍝ Reciprocal in background
       ÷&4        ⍝ Reciprocal in background
0.25
0.25
Line 18: Line 18:
</syntaxhighlight>
</syntaxhighlight>
{{Works in|[[Dyalog APL]]}}
{{Works in|[[Dyalog APL]]}}
The effect of running code in the background can be observed when a measurable amount of time elapses. In the first expression below, get the current time (in milliseconds) and then [[delay]] (<source lang=apl inline>⎕DL</syntaxhighlight>) for each of 1, 2, and 3 seconds, eventually computing the elapsed time, which is slightly more than 1+2+3 seconds (6000 milliseconds). In the second expression, the delaying threads are launched, but we don't await their completion before computing the elapsed time. In the final expression, we synchronise the parallel running delays, giving us a total elapsed time only slightly longer than the longest delay.
The effect of running code in the background can be observed when a measurable amount of time elapses. In the first expression below, get the current time (in milliseconds) and then [[delay]] (<syntaxhighlight lang=apl inline>⎕DL</syntaxhighlight>) for each of 1, 2, and 3 seconds, eventually computing the elapsed time, which is slightly more than 1+2+3 seconds (6000 milliseconds). In the second expression, the delaying threads are launched, but we don't await their completion before computing the elapsed time. In the final expression, we synchronise the parallel running delays, giving us a total elapsed time only slightly longer than the longest delay.
<source lang=apl>
<syntaxhighlight lang=apl>
       t←⎕AI[3] ⋄ ⎕DL¨⍳3 ⋄ ⎕AI[3]-t
       t←⎕AI[3] ⋄ ⎕DL¨⍳3 ⋄ ⎕AI[3]-t
6138
6138

Latest revision as of 10:46, 11 September 2022

&

Spawn (&) is a monadic operator which applies its operand in a new wikipedia:green thread. Rather that returning the result of its operand, Spawn returns a shy thread number. This operator is specific to Dyalog APL.

Usage

Spawn is used to run background tasks, for example for monitoring or handling incoming requests. Since the thread number is returned, ⎕TSYNC ("Thread Synchronise") is provided to retrieve the result, given the thread number. If the result is ready before ⎕TSYNC is used, it prints to the session if applicable.

Spawn is often used in conjunction with the Each operator (¨) to launch multiple threads in parallel.

As Spawn is an operator, it cannot be directly used with a niladic function, since a niladic function is called immediately when its name is referenced. As a workaround, the niladic function can be wrapped in a dfn and called with a dummy argument: {nilFun}&⍬

Examples

      ÷&4         ⍝ Reciprocal in background
0.25
      ⎕←÷&4       ⍝ Show thread number; result prints afterwards
1
0.25
Works in: Dyalog APL

The effect of running code in the background can be observed when a measurable amount of time elapses. In the first expression below, get the current time (in milliseconds) and then delay (⎕DL) for each of 1, 2, and 3 seconds, eventually computing the elapsed time, which is slightly more than 1+2+3 seconds (6000 milliseconds). In the second expression, the delaying threads are launched, but we don't await their completion before computing the elapsed time. In the final expression, we synchronise the parallel running delays, giving us a total elapsed time only slightly longer than the longest delay.

      t←⎕AI[3] ⋄ ⎕DL¨⍳3 ⋄ ⎕AI[3]-t
6138
      t←⎕AI[3] ⋄ ⎕DL&¨⍳3 ⋄ ⎕AI[3]-t
0
      t←⎕AI[3] ⋄ ⎕TSYNC ⎕DL&¨⍳3 ⋄ ⎕AI[3]-t
3046
Works in: Dyalog APL

External links

Lessons

Documentation


APL built-ins [edit]
Primitives (Timeline) Functions
Scalar
Monadic ConjugateNegateSignumReciprocalMagnitudeExponentialNatural LogarithmFloorCeilingFactorialNotPi TimesRollTypeImaginarySquare Root
Dyadic AddSubtractTimesDivideResiduePowerLogarithmMinimumMaximumBinomialComparison functionsBoolean functions (And, Or, Nand, Nor) ∙ GCDLCMCircularComplexRoot
Non-Scalar
Structural ShapeReshapeTallyDepthRavelEnlistTableCatenateReverseRotateTransposeRazeMixSplitEncloseNestCut (K)PairLinkPartitioned EnclosePartition
Selection FirstPickTakeDropUniqueIdentityStopSelectReplicateExpandSet functions (IntersectionUnionWithout) ∙ Bracket indexingIndexCartesian ProductSort
Selector Index generatorGradeIndex OfInterval IndexIndicesDealPrefix and suffix vectors
Computational MatchNot MatchMembershipFindNub SieveEncodeDecodeMatrix InverseMatrix DivideFormatExecuteMaterialiseRange
Operators Monadic EachCommuteConstantReplicateExpandReduceWindowed ReduceScanOuter ProductKeyI-BeamSpawnFunction axis
Dyadic BindCompositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner ProductDeterminantPowerAtUnderRankDepthVariantStencilCutDirect definition (operator)
Quad names Index originComparison toleranceMigration levelAtomic vector