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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <TITLE>Creating APL child tasks under program control</TITLE> <META NAME="DESCRIPTION" CONTENT="APL language help page: Creating APL child tasks under program control"> <META NAME="KEYWORDS" CONTENT="Tasks,Multi-tasking,Child tasks,apl,aplx,apl help"> <!-- %%COMMON_HEAD%% --> <META http-equiv="Content-Type" content="text/html; charset=utf-8"> <LINK rel="stylesheet" type="text/css" href="http://www.microapl.com/styles_apl_help.css"> <!-- %%END%%--> </HEAD> <body> <table> <tr> <td width="800" valign="top" colspan="2"> <center>Topic: <A HREF="ch.htm"><code>APLX Help</code></A> : <A HREF="ch_200.htm"><code>Multi-tasking support</code></A> : <A HREF="ch_200_030.htm"><code>Creating APL child tasks under program control</code></A> </center> <center> [ <A HREF="ch_200_020.htm">Previous</A> | <A HREF="ch_200_040.htm">Next</A> | <A HREF="ch.htm">Contents</A> | <A HREF="help_index.htm">Index</A> | <A HREF="http://www.microapl.co.uk/apl/index.html">APL Home</A> ]</center> <br></td> </tr> <tr> <td width="120"> <a href="http://www.microapl.co.uk/apl/index.html"><img height="68" border="0" width="119" src="MicroAPL_logo.gif" alt="www.microapl.co.uk"></a> </td> <td align="left" valign="bottom"> <h1>Creating APL child tasks under program control</h1> </td> </tr> <tr> <td width="800" valign="top" colspan="2"> <hr> <H2>Creating a new APL task object</H2> <p>You can create child tasks under program control using the 'APL' System Class. This works as follows:</p> <Pre> ChildTask←'⎕' ⎕NEW 'APL' </Pre> <p>This creates a task object, but the APL task itself does not start running until you call the <tt>Open</tt> method. Before doing that, you can set various properties of the new task:</p> <H3>Specifying whether the task runs in the background</H3> <p>By default, child tasks you create will have their own session window. However, if you set the <tt>background</tt> property to 1, the task will not have a session window and all its output will be thrown away (you must set this property before calling the <tt>Open</tt> method). </p> <H3>Specifying the workspace size</H3> <p>By default, a new child task is allocated the amount of workspace which you have set as the default using the Preferences dialog. The <tt>wssize</tt> property allows you to specify a different size, as a value in bytes. If you ask for a very small value, a minimum value of around 100KB will be allocated. If you ask for a very big value, the operating system may allocate a smaller value. A value of 0 means 'use the default'. You must set the <tt>wssize</tt> property before calling the <tt>Open</tt> method, but you can read it back at any time. </p> <H3>Specify which machine the task should run on</H3> <p>If you are running a Client-Server implementation of APLX, you can set the <tt><A HREF="ch_030_030_0367.htm">host</A></tt> property of the APL object to specify on which machine the new APL task should run. You must do this before starting the task.</p> <p>If you have purchased APLX64, your child APL sessions can comprise a mixture of 32-bit and 64-bit tasks. A 32-bit task can start a 64-bit task, and vice versa.</p> <H3>Specifying whether the task's session window is visible</H3> <p>A task which is not a background task will have a session window associated with it, but it may not be visible. You can use the <tt>visible</tt> property (or the <tt>Show</tt> and <tt>Hide</tt> methods) to control whether it is shown, just as you would with any other window. This can be done before or after the <tt>Open</tt> method has been called. You can also use the <tt>where</tt> and <tt>size</tt> properties to set or read the position and size of the task's session window.</p> <H2>Starting the APL task</H2> <p>The actual APL task starts when you call the <tt>Open</tt> method. If the task has a session window, it will be created at this time, and it will appear unless the <tt>visible</tt> property is 0. If the task has a <tt>background</tt> property of 1, nothing will appear. The child task inherits the <code>⎕MOUNT</code> table of its parent, so will initially have the same mapping from library numbers to operating-system directories.</p> <H3>Example</H3> <p>This sequence creates a child task with its own visible session window, and a workspace size of approximately 1MB:</p> <pre> ChildTask←'⎕' ⎕NEW 'APL' ChildTask.wssize←1E6 ChildTask.Open </pre> <p>You can enquire about the visibility and coordinates of the session window as follows:</p> <pre> ChildTask.visible 1 ChildTask.where 12 32 24 64 </pre> <p>You can change the size and position of the task's session window as you would with an ordinary window: </p> <pre> ChildTask.where←4 10 16 50 </pre> <hr> </td> </tr> <tr> <td width="800" valign="top" colspan="2"> <center>Topic: <A HREF="ch.htm"><code>APLX Help</code></A> : <A HREF="ch_200.htm"><code>Multi-tasking support</code></A> : <A HREF="ch_200_030.htm"><code>Creating APL child tasks under program control</code></A> </center> <center> [ <A HREF="ch_200_020.htm">Previous</A> | <A HREF="ch_200_040.htm">Next</A> | <A HREF="ch.htm">Contents</A> | <A HREF="help_index.htm">Index</A> | <A HREF="http://www.microapl.co.uk/apl/index.html">APL Home</A> ]</center> <br></td> </tr> </table> <!-- %%COMMON_BODY_TAIL%% --> <p class="copyright">Copyright © 1996-2010 MicroAPL Ltd</p> <!-- %%END%% --> </body> </html>