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<h1>Creating APL child tasks under program control</h1>
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<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>
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