Class: Promise

• Inheritance
• Description
• Class protocol
  • instance creation
• Instance protocol
  • accessing
  • initialization
  • queries
• Examples

Inheritance:

   Object
   |
   +--Promise
      |
      +--TimedPromise

Package:

stx:libbasic2

Category:

Kernel-Processes

Version:

rev: 1.19 date: 2021/01/20 12:56:04

user: cg

file: Promise.st directory: libbasic2

module: stx stc-classLibrary: libbasic2

Description:

When created, a promise will start to evaluate its block in the background,
and promise to deliver the value of this computation, when asked
for it via #value. 
If an exception happens druing the block evaluate,
it will be delivered  to the value-consumer.

Promises can be used for background computations,
which automatically block the user of the result when that result is needed,
unless the computation finished in the meanwhile.

See also Block>>promise and Lazy/Future in libbasic2.

copyright
COPYRIGHT (c) 1993 by Claus Gittinger
             All Rights Reserved

This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice.   This software may not
be provided or otherwise made available to, or used by, any
other person.  No title to or ownership of the software is
hereby transferred.

Class protocol:

 new

(comment from inherited method)
return an instance of myself without indexed variables

 value: aBlock

create and return a Promise to evaluate aBlock at the current priority

 value: aBlock priority: aPrio

create and return a Promise to evaluate aBlock at some priority

Instance protocol:

 value

return the value of the promise.
If the evaluation process has not yet finished, wait for it.
Otherwise return the value immediately.
Any exception which occurred during the evaluation is forwarded to the
requestor of the value here.

Usage example(s):

value is asked for.

 value: anObject

fake value arrived

 initialize

setup

 value: aBlock priority: aPrio

setup and start the evaluation process.

Usage example(s):

Promise value:[100 timesRepeat:[1000 factorial]] priority:7

Usage example(s):

Promise value:[10 timesRepeat:[1000 factorial]. [self halt] value.] priority:7

 hasValue

return true, if the promise has a value available.
(i.e. if sending #value to it would NOT block)

Examples:

|p|

p := [10000 factorial] promise.
Transcript showCR:'doing something else'.
p value