"       NAME            Parallelism

	AUTHOR          tph@cs.man.ac.uk

	FUNCTION throttled Futures; lazy eval; explicit pa'l'l procs 

	ST-VERSIONS     stx

	PREREQUISITES    

	CONFLICTS       

	DISTRIBUTION    world

	VERSION         1.1

	DATE    22 Jan 1989

	SUMMARY 

Parallelism contains a number of explicitly parallel constructs,

including a new version of Future, Lazy evaluation, and explicit

parallel processes.  Lots of code in here.  Contains an early

version (read: doesn't work) of a ""throttled"" future mechanism.

New version RSN.(2.2).TPH

claus: I have separated the original Parallelism package into

       individual ones: Lazy, Future, ThrottledFuture and ParallelEvaluation

"!

'From Smalltalk-80, version 2, of April 1, 1983 on 29 March 1987 at 5:13:27 pm'!

!Object methodsFor: 'parallel evaluation'!

touch

	"Simply returns self.  If the receiver is an uncompleted

	 Future or Lazy, this forces complete evaluation."

	^self

! !

'From Smalltalk-80, version 2, of April 1, 1983 on 29 March 1987 at 5:09:10 pm'!

Object subclass: #Lazy

	instanceVariableNames: 'result startSemaphore endSemaphore '

	classVariableNames: ''

	poolDictionaries: ''

	category: 'Kernel-Processes'!

Lazy comment:

'I represent an execution which 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.'!

!Lazy methodsFor: 'synchronising'!

doesNotUnderstand: aMessage

	"Any message to a Lazy will end up here."

	startSemaphore signal.          "Start the evaluation."

	endSemaphore wait.              "Wait until evaluation completed."

	endSemaphore signal.            "Wake up anything else."

	^result perform: aMessage selector withArguments: aMessage arguments

		"Perform the message, having re-synchronised."! !

!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 class methodsFor: 'class initialization'!

initialize

	"must avoid the checks"

	superclass := nil

	"Lazy initialize."! !

!Lazy class methodsFor: 'examples'!

example1

	"Evaluates the factorial, starting only when the

	 result is actually required (when printString is sent)."

	| fac |

	fac := [100 factorial] futureValue.

	(Delay forSeconds: 2) wait.

	"Lazy example1"!

example2

	"Starts evaluating both factorials only when required (by the touch),

	 and waits until both blocks have finished before continuing."

	| fac1 fac2 |

	fac2 touch.

	fac1 touch.

	"Lazy example2"!

example3

	"Demonstrates how to pass arguments to a lazy evaluation block."

	| temp |

	temp := [:x :y :z | x * y * z] lazyValueWithArguments: #(2 3 4).

	"Lazy example3"! !

Lazy initialize!

!Block methodsFor: 'parallel evaluation'!

lazyValue

	"Fork a synchronised evaluation of myself. Only starts

	 the evaluation when the result is requested."

	^Lazy new block: self!

lazyValue: aValue

	"Fork a synchronised evaluation of myself. Only starts

	 the evaluation when the result is requested."

	^Lazy new block: self value: aValue!

lazyValue: aValue value: anotherValue

	"Fork a synchronised evaluation of myself. Only starts

	 the evaluation when the result is requested."

	^Lazy new block: self value: aValue value: anotherValue!

lazyValue: aValue value: anotherValue value: bValue

	"Fork a synchronised evaluation of myself. Only starts

	 the evaluation when the result is requested."

	^Lazy new block: self value: aValue value: anotherValue value: bValue!

lazyValueWithArguments: anArray

	"Fork a synchronised evaluation of myself. Only starts

	 the evaluation when the result is requested."

	^Lazy new block: self valueWithArguments: anArray

! !

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"!