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{{Built-in|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]].
|<code>&</code>
|}
==== {R}←{X}f&Y ====


& is a monadic operator with an ambivalent derived function. & spawns a new thread in which f is applied to its argument Y (monadic case) or between its arguments X and Y (dyadic case). The shy result of this application is the number of the newly created thread.
== Usage ==


When function f terminates, its result (if any), the thread result, is returned.
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</source> ("Thread Synchronise") is provided to retrieve the result, given the thread number. If the result is ready before <source lang=apl inline>⎕TSYNC</source> is used, it prints to the [[session]] if applicable.


⎕TSYNC, used monadically, given the thread number can be used to wait for a result from that thread.
Spawn is often used in conjunction with the [[Each]] operator (<source lang=apl inline>¨</source>) to launch multiple threads in parallel.
If no ⎕TSYNC is in effect, the thread result is displayed in the session in the normal fashion.


 
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}&⍬</source>
Note that & can be used in conjunction with the each operator ¨ to launch many threads in parallel.


== Examples ==
== Examples ==
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       ÷&4        ⍝ Reciprocal in background
       ÷&4        ⍝ Reciprocal in background
0.25
0.25
       ⎕←÷&4      ⍝ Show thread number
       ⎕←÷&4      ⍝ Show thread number; result prints afterwards
1
1
0.25
0.25
      FOO&88      ⍝ Spawn monadic function.
      2 FOO&3    ⍝ dyadic
      {NIL}&0    ⍝ niladic
      ⍎&'NIL'    ⍝ ..
      X.GOO&99    ⍝ thread in remote space.
      ⍎&'⎕dl 2'  ⍝ Execute async expression.
      'NS'⍎&'FOO' ⍝ .. remote .. .. ..
      PRT&¨↓⎕nl 9 ⍝ PRT spaces in parallel.
</source>
</source>
{{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</source>) 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>
      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
</source>
{{Works in|[[Dyalog APL]]}}
== External links ==
=== Lessons ===
* [https://chat.stackexchange.com/rooms/52405/conversation/lesson-26-concurrent-apl-threads APL Cultivation]
=== Documentation ===
* [https://help.dyalog.com/latest/#Language/Primitive%20Operators/Spawn.htm Dyalog]
{{APL built-ins}}[[Category:Primitive operators]]

Revision as of 08:00, 8 August 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 Conjugate ∙ Negate ∙ Signum ∙ Reciprocal ∙ Magnitude ∙ Exponential ∙ Natural Logarithm ∙ Floor ∙ Ceiling ∙ Factorial ∙ Not ∙ Pi Times ∙ Roll ∙ Type ∙ Imaginary ∙ Square Root ∙ Round
Dyadic Add ∙ Subtract ∙ Times ∙ Divide ∙ Residue ∙ Power ∙ Logarithm ∙ Minimum ∙ Maximum ∙ Binomial ∙ Comparison functions ∙ Boolean functions (And, Or, Nand, Nor) ∙ GCD ∙ LCM ∙ Circular ∙ Complex ∙ Root
Non-Scalar
Structural Shape ∙ Reshape ∙ Tally ∙ Depth ∙ Ravel ∙ Enlist ∙ Table ∙ Catenate ∙ Reverse ∙ Rotate ∙ Transpose ∙ Raze ∙ Mix ∙ Split ∙ Enclose ∙ Nest ∙ Cut (K) ∙ Pair ∙ Link ∙ Partitioned Enclose ∙ Partition
Selection First ∙ Pick ∙ Take ∙ Drop ∙ Unique ∙ Identity ∙ Stop ∙ Select ∙ Replicate ∙ Expand ∙ Set functions (Intersection ∙ Union ∙ Without) ∙ Bracket indexing ∙ Index ∙ Cartesian Product ∙ Sort
Selector Index generator ∙ Grade ∙ Index Of ∙ Interval Index ∙ Indices ∙ Deal ∙ Prefix and suffix vectors
Computational Match ∙ Not Match ∙ Membership ∙ Find ∙ Nub Sieve ∙ Encode ∙ Decode ∙ Matrix Inverse ∙ Matrix Divide ∙ Format ∙ Execute ∙ Materialise ∙ Range
Operators Monadic Each ∙ Commute ∙ Constant ∙ Replicate ∙ Expand ∙ Reduce ∙ Windowed Reduce ∙ Scan ∙ Outer Product ∙ Key ∙ I-Beam ∙ Spawn ∙ Function axis ∙ Identity (Null, Ident)
Dyadic Bind ∙ Compositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner Product ∙ Determinant ∙ Power ∙ At ∙ Under ∙ Rank ∙ Depth ∙ Variant ∙ Stencil ∙ Cut ∙ Direct definition (operator) ∙ Identity (Lev, Dex)
Quad names Index origin ∙ Comparison tolerance ∙ Migration level ∙ Atomic vector
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