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<H1><A NAME="SECTION04780000000000000000">Error Handling in the BLACS</A></H1>
<P>
<A NAME="6342"> </A>
<P>
This section describes the BLACS error-handling features. The BLACS error-handling behavior may be changed at compile time by using the C preprocessor
macro <TT>BlacsDebugLvl</TT>.
a call to BLACS_GET (see
[<A HREF="node189.html#lawn94">54</A>] for details) will help determine
what debug level the BLACS
are using.
<P>
If the BLACS are compiled with a BLACS debug level of 0, little
error checking is performed. A few critical items will be checked
(for instance, BLACS_GRIDINIT will still not allow the user to allocate a
process grid with more processes than there are available), but for
performance reasons, the BLACS will not check most of the parameters.
<P>
It is therefore highly recommended that users link their code to a BLACS
library compiled with debug level 1 while debugging their code. BLACS debug
level 1 mainly does parameter checking. A few other services are also
provided. For instance, users will be warned if a process sends a message
to itself. Having a process send to itself is legal, but it displays
poor performance and requires enough buffer space that it can occasionally
cause hangs for large messages. The BLACS therefore issue a warning when
this behavior is detected.
<P>
Many times, the debug level 0 code will simply hang, leaving the developer
without any clue as to what has gone wrong. This may be caused, for
instance, by trying to receive from a process that is not in the current
context. The debug level 1 BLACS can detect this type of user error, and
issue a (we hope helpful) message.
<P>
The BLACS issue three types of messages:
<P>
<OL>
<LI> <EM>BLACS warning</EM>: BLACS detect risky behavior, but attempt to correct
or ignore. Warning message is printed, and execution proceeds.
<LI> <EM>BLACS error</EM>: BLACS detects an error, prints an error message,
and kills the machine via a call to BLACS_ABORT.
<LI> <EM>System error</EM>: The BLACS receive an error message from the underlying
system, which is then passed on to the user, and the BLACS kills the machine.
</OL><BR> <HR>
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<P><ADDRESS>
<I>Susan Blackford <BR>
Tue May 13 09:21:01 EDT 1997</I>
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