"

 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:goodies' }"

	instanceVariableNames:'result semaphore'

	classVariableNames:''

	poolDictionaries:''

	category:'Kernel-Processes'

!

!Future 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 in progress.  

    Any messages sent to me are delayed until execution has completed.'

"

!

examples

"

  Starts evaluating the factorial immediately, but waits until

  the result is available before printing the answer

								    [exBegin]

    | fac |

    fac := [100 factorial] futureValue.

    Transcript showCR: 'evaluating factorial...'.

    Transcript showCR: fac printString

								    [exEnd]

  An example illustrating the use of multiple futures and

  explicit resynchronisation.

  Starts evaluating both factorials immediately, but waits until

  both blocks have finished before continuing.

								    [exBegin]

    | fac1 fac2 |

    fac1 := [Transcript showCR: 'Starting fac1.. '. 1000 factorial] futureValue.

    fac2 := [Transcript showCR: 'Starting fac2.. '. 2000 factorial] futureValue.

    fac2 touch.

    fac1 touch.

    Transcript showCR: 'both completed.'.

								    [exEnd]

  Example showing how arguments may be passed to futures.

								    [exBegin]

    | temp |

    temp := [:x :y | 10 * x * y] futureValue: 3 value: 4.

    Transcript  showCR: temp printString.

								    [exEnd]

  Claus:

    The above examples do not really show the power of Futures;

    they can be useful, whenever some long-time computation is

    to be done, and some other useful work can be done in the meanwhile.

    for example:

    Here, the input is read before - the readTime and view creation

    times sum up:

								    [exBegin]

	|p text v|

	p := PipeStream readingFrom:'ls -l /bin /usr/bin /usr/lib'.

	text := p contents.

	p close.

	v := TextView new openAndWait.

	v contents:text

								    [exEnd]

    The same here:

								    [exBegin]

	|p text v|

	v := TextView new openAndWait.

	p := PipeStream readingFrom:'ls -l /bin /usr/bin /usr/lib'.

	text := p contents.

	p close.

	v contents:text

								    [exEnd]

    Here, the view creation and reading are done in parallel:

    (if the user is slow when opening the view, the contents may

     be already available)

								    [exBegin]

	|p text v|

	text := [   |p t|

		    p := PipeStream readingFrom:'ls -l /bin /usr/bin /usr/lib'.

		    t := p contents.

		    p close.

		    t

		] futureValue.

	v := TextView new openAndWait.

	v contents:text

								    [exEnd]

"

! !

!Future class methodsFor:'class initialization'!

initialize

	"must avoid the checks"

	superclass := nil

	"Future initialize."

! !

!Future methodsFor:'evaluating'!

block: aBlock

	"Execute aBlock in parallel with whatever called me, but

	 ensure that any messages sent to me before execution

	 of the block has terminated are suspended until it has terminated."

	semaphore := Semaphore new.

	[result := aBlock value.  semaphore signal] fork

!

block: aBlock value: aValue

	"Execute aBlock in parallel with whatever called me, but

	 ensure that any messages sent to me before execution

	 of the block has terminated are suspended until it has terminated."

	semaphore := Semaphore new.

	[result := aBlock value: aValue.  semaphore signal] fork

!

block: aBlock value: value1 value: value2

	"Execute aBlock in parallel with whatever called me, but

	 ensure that any messages sent to me before execution

	 of the block has terminated are suspended until it has terminated."

	semaphore := Semaphore new.

	[result := aBlock value: value1 value: value2.

	 semaphore signal] fork

!

block: aBlock value: value1 value: value2 value: value3

	"Execute aBlock in parallel with whatever called me, but

	 ensure that any messages sent to me before execution

	 of the block has terminated are suspended until it has terminated."

	semaphore := Semaphore new.

	[result := aBlock value: value1 value: value2 value: value3.

	 semaphore signal] fork

!

block: aBlock valueWithArguments: anArray

	"Execute aBlock in parallel with whatever called me, but

	 ensure that any messages sent to me before execution

	 of the block has terminated are suspended until it has terminated."

	semaphore := Semaphore new.

	[result := aBlock valueWithArguments: anArray.

	 semaphore signal] fork

! !

!Future methodsFor:'synchronising'!

doesNotUnderstand: aMessage

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

        semaphore waitUncounted.     "Wait for evaluation to complete"

                                    "(if not already completed)"

        ^result perform: aMessage selector 

                withArguments: aMessage arguments

!

hasValue

        ^ semaphore wouldBlock not

! !

!Future class methodsFor:'documentation'!

version

! !

Future initialize!