"{ Encoding: utf8 }"
"
This is a Manchester Goodie protected by copyright.
These conditions are imposed on the whole Goodie, and on any significant
part of it which is separately transmitted or stored:
* You must ensure that every copy includes this notice, and that
source and author(s) of the material are acknowledged.
* These conditions must be imposed on anyone who receives a copy.
* The material shall not be used for commercial gain without the prior
written consent of the author(s).
Further information on the copyright conditions may be obtained by
sending electronic mail:
To: goodies-lib@cs.man.ac.uk
Subject: copyright
or by writing to The Smalltalk Goodies Library Manager, Dept of
Computer Science, The University, Manchester M13 9PL, UK
(C) Copyright 1992 University of Manchester
For more information about the Manchester Goodies Library (from which
this file was distributed) send e-mail:
To: goodies-lib@cs.man.ac.uk
Subject: help
"
"{ Package: 'stx:libbasic2' }"
"{ NameSpace: Smalltalk }"
ProtoObject subclass:#Lazy
instanceVariableNames:'result startSemaphore endSemaphore'
classVariableNames:''
poolDictionaries:''
category:'Kernel-Processes'
!
!Lazy class methodsFor:'documentation'!
copyright
"
This is a Manchester Goodie protected by copyright.
These conditions are imposed on the whole Goodie, and on any significant
part of it which is separately transmitted or stored:
* You must ensure that every copy includes this notice, and that
source and author(s) of the material are acknowledged.
* These conditions must be imposed on anyone who receives a copy.
* The material shall not be used for commercial gain without the prior
written consent of the author(s).
Further information on the copyright conditions may be obtained by
sending electronic mail:
To: goodies-lib@cs.man.ac.uk
Subject: copyright
or by writing to The Smalltalk Goodies Library Manager, Dept of
Computer Science, The University, Manchester M13 9PL, UK
(C) Copyright 1992 University of Manchester
For more information about the Manchester Goodies Library (from which
this file was distributed) send e-mail:
To: goodies-lib@cs.man.ac.uk
Subject: help
"
!
documentation
"
I represent an execution which may or may not be required.
I will not start execution until at least one message has been received.
The messages sent to me are delayed until execution has completed.
[author:]
tph@cs.man.ac.uk
[see also:]
Block LazyValue Future
"
!
examples
"
Evaluates the factorial, starting only when the
result is actually required (when printString is sent).
[exBegin]
| fac |
fac := [100 factorial] lazyValue.
Transcript showCR: 'Doing nothing. '.
(Delay forSeconds: 2) wait.
Transcript showCR: fac printString.
[exEnd]
Starts evaluating both factorials only when required (by the value),
and waits until both blocks have finished before continuing.
[exBegin]
| fac1 fac2 |
fac1 := [Transcript showCR: 'Starting fac1.. '. 100 factorial] lazyValue.
fac2 := [Transcript showCR: 'Starting fac2.. '. 120 factorial] lazyValue.
fac2 value.
fac1 value.
Transcript showCR: 'both completed.'.
[exEnd]
Demonstrates how to pass arguments to a lazy evaluation block.
[exBegin]
| temp |
temp := [:x :y :z | x * y * z] lazyValueWithArguments: #(2 3 4).
Transcript showCR: temp printString.
[exEnd]
"
! !
!Lazy methodsFor:'evaluating'!
block: aBlock
"Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver."
startSemaphore := Semaphore new.
endSemaphore := Semaphore new.
[
startSemaphore wait.
result := aBlock value.
endSemaphore signal
] fork.
!
block: aBlock value: aValue
"Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver."
startSemaphore := Semaphore new.
endSemaphore := Semaphore new.
[
startSemaphore wait.
result := aBlock value: aValue.
endSemaphore signal
] fork
!
block: aBlock value: value1 value: value2
"Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver."
startSemaphore := Semaphore new.
endSemaphore := Semaphore new.
[
startSemaphore wait.
result := aBlock value: value1 value: value2.
endSemaphore signal
] fork
!
block: aBlock value: value1 value: value2 value: value3
"Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver."
startSemaphore := Semaphore new.
endSemaphore := Semaphore new.
[
startSemaphore wait.
result := aBlock value: value1 value: value2 value: value3.
endSemaphore signal
] fork
!
block: aBlock valueWithArguments: anArray
"Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver."
startSemaphore := Semaphore new.
endSemaphore := Semaphore new.
[
startSemaphore wait.
result := aBlock valueWithArguments: anArray.
endSemaphore signal
] fork
! !
!Lazy methodsFor:'printing'!
displayOn:aGCOrStream
"notice: displayString and displayOn: will not wait for the value (they are for developers and inspectors),
whereas printString and printOn: will wait (they are for the program to print data)."
"/ what a kludge - Dolphin and Squeak mean: printOn: a stream;
"/ ST/X (and some old ST80's) mean: draw-yourself on a GC.
(aGCOrStream isStream) ifFalse:[
^ self _evaluate_ displayOn:aGCOrStream
].
startSemaphore isNil ifTrue:[
result displayOn:aGCOrStream.
aGCOrStream nextPutAll:' (Lazy evaluated)'.
^ self.
].
aGCOrStream nextPutAll:'Lazy (unevaluated)'
"Modified (comment): / 25-06-2019 / 10:49:32 / Claus Gittinger"
!
displayString
"notice: displayString and displayOn: will not wait for the value (they are for developers and inspectors),
whereas printString and printOn: will wait (they are for the program to print data)."
"defined here, because I inherit from nobody"
^ (Object compiledMethodAt:#displayString)
valueWithReceiver:self
arguments:nil
selector:#displayString
"Modified (comment): / 25-06-2019 / 10:49:36 / Claus Gittinger"
! !
!Lazy methodsFor:'synchronising'!
_evaluate_
"answer the computed value"
|startSema endSema|
startSema := startSemaphore.
startSema notNil ifTrue:[
startSema signal. "Start the evaluation."
endSema := endSemaphore.
endSema notNil ifTrue:[
endSema waitUncounted. "Wait until evaluation completed."
].
startSemaphore := endSemaphore := nil.
].
^ result
!
doesNotUnderstand: aMessage
"Any message to a Lazy will end up here."
startSemaphore notNil ifTrue:[
Processor activeProcess isDebuggerProcess ifTrue:[
"enable debugging / inspecting without evaluating"
^ aMessage sendTo:self usingClass:Object.
].
self _evaluate_.
].
^ aMessage sendTo:result.
"Modified: / 01-02-2018 / 10:17:27 / stefan"
!
perform:aSelector withArguments:argArray
"send the message aSelector with all args taken from argArray
to the receiver."
startSemaphore notNil ifTrue:[
Processor activeProcess isDebuggerProcess ifTrue:[
"enable debugging / inspecting"
^ super perform:aSelector withArguments:argArray.
].
self _evaluate_.
].
^ result perform:aSelector withArguments:argArray.
"Modified: / 01-02-2018 / 10:17:08 / stefan"
! !
!Lazy methodsFor:'testing'!
isLazyValue
"true if I have no value yet
(i.e. would block when sending me a message)"
^ endSemaphore wouldBlock
"Modified (comment): / 25-06-2019 / 11:08:45 / Claus Gittinger"
! !
!Lazy class methodsFor:'documentation'!
version
^ '$Header$'
!
version_CVS
^ '$Header$'
! !