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<TITLE>LambdaMOO Programmer's Manual - Aborted Tasks</TITLE>
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<H3><A NAME="SEC71" HREF="ProgrammersManual_toc.html#TOC71">Controlling the Handling of Aborted Tasks</A></H3>
<P>
The server will abort the execution of tasks for either of two reasons:
<OL>
<LI>an error was raised within the task but not caught, or
<LI>the task exceeded the limits on ticks and/or seconds.
</OL>
<P>
In each case, after aborting the task, the server attempts to call a particular
<STRONG>handler verb</STRONG> within the database to allow code there to handle this
mishap in some appropriate way. If this verb call suspends or returns a true
value, then it is considered to have handled the situation completely and no
further processing will be done by the server. On the other hand, if the
handler verb does not exist, or if the call either returns a false value
without suspending or itself is aborted, the server takes matters into its own
hands.
</P>
<P>
First, an error message and a MOO verb-call stack <STRONG>traceback</STRONG> are
printed to the player who typed the command that created the original aborted
task, explaining why the task was aborted and where in the task the problem
occurred. Then, if the call to the handler verb was itself aborted, a second
error message and traceback are printed, describing that problem as well. Note
that if the handler-verb call itself is aborted, no further `nested' handler
calls are made; this policy prevents what might otherwise be quite a vicious
little cycle.
</P>
<P>
The specific handler verb, and the set of arguments it is passed, differs for
the two causes of aborted tasks.
</P>
<P>
If an error is raised and not caught, then the verb-call
<PRE>
$handle_uncaught_error(<VAR>code</VAR>, <VAR>msg</VAR>, <VAR>value</VAR>, <VAR>traceback</VAR>, <VAR>formatted</VAR>)
</PRE>
<P>
is made, where <VAR>code</VAR>, <VAR>msg</VAR>, <VAR>value</VAR>, and <VAR>traceback</VAR> are the
values that would have been passed to a handler in a <CODE>try</CODE>-<CODE>except</CODE>
statement and <VAR>formatted</VAR> is a list of strings being the lines of error and
traceback output that will be printed to the player if
<CODE>$handle_uncaught_error</CODE> returns false without suspending.
</P>
<P>
If a task runs out of ticks or seconds, then the verb-call
<PRE>
$handle_task_timeout(<VAR>resource</VAR>, <VAR>traceback</VAR>, <VAR>formatted</VAR>)
</PRE>
<P>
is made, where <VAR>resource</VAR> is the appropriate one of the strings
<CODE>"ticks"</CODE> or <CODE>"seconds"</CODE>, and <VAR>traceback</VAR> and <VAR>formatted</VAR> are
as above.
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