Daemon example: Difference between revisions
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Sirius '''Daemons''' are a class of objects that run on a thread other than the user that launched them. | Sirius '''Daemons''' are a class of objects that run on a thread other than the user that launched them. The thread that launches the <var>Daemon</var> is called the "parent". The <var>Daemon</var> responds to requests from the parent and may optionally pass back to the parent thread the results of commands and <var class="product">[[User Language]]</var> programs. | ||
See the [[Daemon class]] and | See the [[Daemon class|Daemon class]] and its method pages for detailed information about <var>Daemon</var> behaviors. | ||
=Why use a Daemon?= | ==Why use a Daemon?== | ||
<var>Daemon</var> objects make it easy to capture command output and <var class="product">User Language</var> output to <var>Stringlist</var> objects. They make it easy to keep server sizes low by splitting work between a parent and daemon. The use of Asynchronous daemons allows work to be discharged in "fire and forget" mode, where the <var>Daemon</var> completes a task while the parent thread moves on to other processes. | |||
==Variable Find conditions== | |||
One problem often encountered in <var class="product">User Language</var> is that <var>Find</var> conditions are bound at compile time. Variable input to a fixed number of conditions, with an unchanging set of field names, is handled well in ordinary <var class="product">User Language</var>. But <var class="product">User Language</var> has no clean mechanism to programmatically set up and execute dynamically generated <var>Find</var>s. | |||
Daemons handle this situation very elegantly. In the following program, a <var>Daemon</var> is instantiated, and a small program is built to <var>Find</var> a set of records. The program is submitted to the <var>Daemon</var> in a <var>[[Stringlist class|Stringlist]]</var>, and the resulting set of found records is returned to the parent thread in a <var>[[Recordset class#SortedRecordSet|SortedRecordSet]]</var> object. | |||
<p class="code">Begin | |||
Daemons handle this situation very elegantly. | |||
%FindCriteria is string len 255 | |||
%Pazuzu is object Daemon | |||
%Sorted is object SortedRecordSet in file CUSTOMER | |||
%SubList is object stringList | |||
* Any of a variety of FIND conditions can be submitted to the Daemon. | |||
* In a full application, these conditions could be selected by the user through | |||
* a screen or browser interface. | |||
* %FindCriteria = 'RECTYPE = ''C'' ' | |||
* %FindCriteria = 'NICKNAME IS LIKE ''SI*'' ' | |||
%FindCriteria = 'RECTYPE = ''C'' AND LAST_MODIFIED=20101225' | |||
%SubList = new | |||
Text to %SubList | |||
Begin | |||
%BasicSet is object RecordSet in file CUSTOMER | |||
%Sorted is object SortedRecordSet in file CUSTOMER | |||
%BasicSet = New | |||
Find Records to %BasicSet | |||
{%FindCriteria} | |||
End Find | |||
Sort records in %BasicSet to %Sorted by NICKNAME | |||
%(daemon):returnObject(%Sorted) | |||
End | |||
End Text | |||
%Pazuzu = New | |||
%Pazuzu:open('CUSTOMER') | |||
%Pazuzu:run(%SubList,,%Sorted) | |||
* Process the returned sorted list | |||
For each record in %Sorted | |||
feoname: feo NAME | |||
print NICKNAME and NAME(occurrence in feoname) and TCPADDR(occurrence in feoname) | |||
End For | |||
End For | |||
End | |||
</p> | |||
[[Daemon class]] | ==See also== | ||
<ul> | |||
<li>[[Daemon class]] | |||
[[Daemon methods]] | <li>[[List of Daemon methods]] | ||
[[Stringlist class]] | <li>[[Stringlist class]] | ||
[[Recordset class]] | <li>[[Recordset class]] | ||
</ul> | |||
Revision as of 23:14, 7 December 2012
Sirius Daemons are a class of objects that run on a thread other than the user that launched them. The thread that launches the Daemon is called the "parent". The Daemon responds to requests from the parent and may optionally pass back to the parent thread the results of commands and User Language programs.
See the Daemon class and its method pages for detailed information about Daemon behaviors.
Why use a Daemon?
Daemon objects make it easy to capture command output and User Language output to Stringlist objects. They make it easy to keep server sizes low by splitting work between a parent and daemon. The use of Asynchronous daemons allows work to be discharged in "fire and forget" mode, where the Daemon completes a task while the parent thread moves on to other processes.
Variable Find conditions
One problem often encountered in User Language is that Find conditions are bound at compile time. Variable input to a fixed number of conditions, with an unchanging set of field names, is handled well in ordinary User Language. But User Language has no clean mechanism to programmatically set up and execute dynamically generated Finds.
Daemons handle this situation very elegantly. In the following program, a Daemon is instantiated, and a small program is built to Find a set of records. The program is submitted to the Daemon in a Stringlist, and the resulting set of found records is returned to the parent thread in a SortedRecordSet object.
Begin %FindCriteria is string len 255 %Pazuzu is object Daemon %Sorted is object SortedRecordSet in file CUSTOMER %SubList is object stringList * Any of a variety of FIND conditions can be submitted to the Daemon. * In a full application, these conditions could be selected by the user through * a screen or browser interface. * %FindCriteria = 'RECTYPE = C ' * %FindCriteria = 'NICKNAME IS LIKE SI* ' %FindCriteria = 'RECTYPE = C AND LAST_MODIFIED=20101225' %SubList = new Text to %SubList Begin %BasicSet is object RecordSet in file CUSTOMER %Sorted is object SortedRecordSet in file CUSTOMER %BasicSet = New Find Records to %BasicSet {%FindCriteria} End Find Sort records in %BasicSet to %Sorted by NICKNAME %(daemon):returnObject(%Sorted) End End Text %Pazuzu = New %Pazuzu:open('CUSTOMER') %Pazuzu:run(%SubList,,%Sorted) * Process the returned sorted list For each record in %Sorted feoname: feo NAME print NICKNAME and NAME(occurrence in feoname) and TCPADDR(occurrence in feoname) End For End For End