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Class: OperationQueue


Inheritance:

   Object
   |
   +--OperationQueue

Package:
stx:libbasic2
Category:
Kernel-Processes
Version:
rev: 1.10 date: 2017/05/22 10:20:40
user: mawalch
file: OperationQueue.st directory: libbasic2
module: stx stc-classLibrary: libbasic2
Author:
Martin Walser
Claus Gittinger

Description:


An operationQueue allows operations (i.e. actions) to be evaluated in
a first-come-first-serve queue like fashion. A single consumer process
waits for orders to be enqueued and evaluates them (as they come).
Producer processes which want to have some operation performed may
enqueue these. Producers are suspended, until the operation is finished.
If multiple orders which compare equal are enqueued by multiple producers,
the operation is only evaluated once, and both producers will wake up when
the operation has finished.


Related information:

    SharedQueue
    Queue

Class protocol:

instance creation
o  new

o  new: n


Instance protocol:

accessing
o  consumerProcess
return the value of the instance variable 'consumerProcess' (automatically generated)

o  consumerProcessPriority
return the value of the instance variable 'consumerProcessPriority' (automatically generated)

o  consumerProcessPriority: something
set the value of the instance variable 'consumerProcessPriority' (automatically generated)

consumer
o  fetchNextOperationAndExecute
dequeue the next order, evaluate it and wake up waiters

o  startConsumerProcess

o  stopConsumerProcess

debugging support
o  copyContextChain: aContext
dequeue the next order, evaluate it and wake up waiters

o  linkContextChain: aConsumerChain
for debugging - concatenate aConsumerChain to my own context chain (to make debugging easier)

initialization
o  initializeLock

producer
o  scheduleOperation: anotherOperation
enqueue an order (something that understands #value) to the op-queue;
wait until the operation has performed (#value been sent),
return the result of the #value send.
If a similar order is already in the queue, wait for that one to finish.

o  scheduleOperation: anotherOperation asynchronous: asynchronous
enqueue an order (something that understands #value) to the op-queue;
if asynchronous is false, wait until the operation has performed (#value been sent),
return the result of the #value send.
If a similar order is already in the queue, wait for that one to finish.
If asynchronous is true, do not wait (but also: do not return a return value)

queries
o  size
return the number of operations in the queue


Private classes:

    OperationInQueue

Examples:


two orders; done sequentially:
    |opQ|

    opQ := OperationQueue new.
    opQ scheduleOperation:[ Transcript showCR:'hello world-1'].
    opQ scheduleOperation:[ Transcript showCR:'hello world-2'].

only 10 outputs (same operation entered by multiple producers):
    |p1 p2 p3 opQ order|

    opQ := OperationQueue new.
    order := [ Transcript showCR:'hello world '].
    p1 := [
            1 to:10 do:[:i |
                opQ scheduleOperation:order.
            ]
          ] fork.
    p2 := [
            1 to:10 do:[:i |
                opQ scheduleOperation:order.
            ]
          ] fork.
    p3 := [
            1 to:10 do:[:i |
                opQ scheduleOperation:order.
            ]
          ] fork.


ST/X 7.1.0.0; WebServer 1.663 at exept.de:8081; Wed, 19 Sep 2018 01:15:31 GMT