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194 lines
6.8 KiB
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<H1><A NAME="SECTION00090000000000000000">
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Error handling</A>
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</H1>
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<P>
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The PSBLAS library error handling policy has been completely rewritten
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in version 2.0. The idea behind the design of this new error handling
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strategy is to keep error messages on a stack allowing the user to
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trace back up to the point where the first error message has been
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generated. Every routine in the PSBLAS-2.0 library has, as last
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non-optional argument, an integer <code>info</code> variable; whenever,
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inside the routine, an error is detected, this variable is set to a
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value corresponding to a specific error code. Then this error code is
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also pushed on the error stack and then either control is returned to
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the caller routine or the execution is aborted, depending on the users
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choice. At the time when the execution is aborted, an error message is
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printed on standard output with a level of verbosity than can be
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chosen by the user. If the execution is not aborted, then, the caller
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routine checks the value returned in the <code>info</code> variable and, if
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not zero, an error condition is raised. This process continues on all the
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levels of nested calls until the level where the user decides to abort
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the program execution.
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<P>
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Figure <A HREF="#fig:routerr">9</A> shows the layout of a generic <code>psb_foo</code>
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routine with respect to the PSBLAS-2.0 error handling policy. It is
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possible to see how, whenever an error condition is detected, the
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<code>info</code> variable is set to the corresponding error code which is,
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then, pushed on top of the stack by means of the
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<code>psb_errpush</code>. An error condition may be directly detected inside
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a routine or indirectly checking the error code returned returned by a
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called routine. Whenever an error is encountered, after it has been
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pushed on stack, the program execution skips to a point where the
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error condition is handled; the error condition is handled either by
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returning control to the caller routine or by calling the
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<code>psb\_error</code> routine which prints the content of the error stack
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and aborts the program execution, according to the choice made by the
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user with <code>psb_set_erraction</code>. The default is to print the error
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and terminate the program, but the user may choose to handle the error
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explicitly.
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<P>
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<DIV ALIGN="CENTER"><A NAME="fig:routerr"></A><A NAME="6774"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 9:</STRONG>
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The layout of a generic <TT>psb_foo</TT>
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routine with respect to PSBLAS-2.0 error handling policy.</CAPTION>
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<TR><TD>
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<BR>
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<DIV ALIGN="CENTER">
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<!-- MATH
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$\fbox{\TheSbox}$
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-->
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<IMG
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</DIV></TD></TR>
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</TABLE>
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</DIV>
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<P>
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Figure <A HREF="#fig:errormsg">10</A> reports a sample error message generated by
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the PSBLAS-2.0 library. This error has been generated by the fact that
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the user has chosen the invalid ``FOO'' storage format to represent
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the sparse matrix. From this error message it is possible to see that
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the error has been detected inside the <code>psb_cest</code> subroutine
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called by <code>psb_spasb</code> ... by process 0 (i.e. the root process).
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<P>
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<DIV ALIGN="CENTER"><A NAME="fig:errormsg"></A><A NAME="6775"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 10:</STRONG>
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A sample PSBLAS-2.0 error
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message. Process 0 detected an error condition inside the psb_cest subroutine</CAPTION>
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<!-- MATH
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-->
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<IMG
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</DIV></TD></TR>
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</TABLE>
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</DIV>
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<P>
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<BR><HR>
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<!--Table of Child-Links-->
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<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>
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<UL>
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<LI><A NAME="tex2html1478"
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HREF="node102.html">psb_errpush -- Pushes an error code onto the error
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stack</A>
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<LI><A NAME="tex2html1479"
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HREF="node103.html">psb_error -- Prints the error stack content and aborts
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execution</A>
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<LI><A NAME="tex2html1480"
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HREF="node104.html">psb_set_errverbosity -- Sets the verbosity of error
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messages.</A>
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<LI><A NAME="tex2html1481"
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HREF="node105.html">psb_set_erraction -- Set the type of action to be
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taken upon error condition.</A>
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</UL>
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