| 63 |
|
|
| 64 |
For run--time package control, MITgcm uses flags set through a |
For run--time package control, MITgcm uses flags set through a |
| 65 |
\texttt{data.pkg} file. While some packages (\textit{eg.} |
\texttt{data.pkg} file. While some packages (\textit{eg.} |
| 66 |
\texttt{debug}, \texttt{mnc}, \texttt{cost}) may have their own |
\texttt{debug}, \texttt{mnc}, \texttt{exch2}) may have their own usage |
| 67 |
conventions, most follow a simple flag naming convention of the |
conventions, most follow a simple flag naming convention of the form: |
|
form: |
|
| 68 |
\begin{verbatim} |
\begin{verbatim} |
| 69 |
usePackageName=.TRUE. |
usePackageName=.TRUE. |
| 70 |
\end{verbatim} |
\end{verbatim} |
| 71 |
where the \texttt{usePackageName} variable can activate or disable the |
where the \texttt{usePackageName} variable can activate or disable the |
| 72 |
package at runtime. |
package at runtime. As mentioned previously, packages must be |
| 73 |
|
included in order to be activated. Generally, such mistakes will be |
| 74 |
|
detected and reported as errors by the code. However, users should |
| 75 |
|
still be aware of the dependency. |
| 76 |
|
|
| 77 |
|
|
| 78 |
%\subsection{Modifying or Creating Packages} |
\section{Package Coding Standards} |
| 79 |
|
|
| 80 |
|
The following sections describe how to modify and/or create new MITgcm |
| 81 |
|
packages. |
| 82 |
|
|
| 83 |
|
\subsection{Packages are Not Libraries} |
| 84 |
|
|
| 85 |
|
To a beginner, the MITgcm packages may resemble libraries as used in |
| 86 |
|
myriad software projects. While future versions are likely to |
| 87 |
|
implement packages as libraries (perhaps using FORTRAN90/95 syntax) |
| 88 |
|
the current packages (FORTRAN77) are \textbf{not} based upon any |
| 89 |
|
concept of libraries. |
| 90 |
|
|
| 91 |
|
\subsubsection{File ``Hiding'' Rules} |
| 92 |
|
|
| 93 |
|
Instead, packages should be viewed only as directories containing |
| 94 |
|
``sets of source files'' that are built using some simple mechanisms |
| 95 |
|
provided by \texttt{genmake2}. Conceptually, the build process adds |
| 96 |
|
files as they are found and proceeds according to the following rules: |
| 97 |
|
\begin{enumerate} |
| 98 |
|
\item \texttt{genmake2} locates a ``core'' or main set of source files |
| 99 |
|
(the \texttt{-standarddirs} option sets these locations and the |
| 100 |
|
default value contains the directories \texttt{eesupp} and |
| 101 |
|
\texttt{model}). |
| 102 |
|
|
| 103 |
|
\item \texttt{genmake2} then finds additional source files by |
| 104 |
|
inspecting the contents of each of the package directories: |
| 105 |
|
\begin{enumerate} |
| 106 |
|
\item As the new files are found, they are added to a list of source |
| 107 |
|
files. |
| 108 |
|
|
| 109 |
|
\item If there is a file name ``collision'' (that is, if one of the |
| 110 |
|
files in a package has the same name as one of the files |
| 111 |
|
previously encountered) then the file within the newer (more |
| 112 |
|
recently visited) package will superseed (or ``hide'') any |
| 113 |
|
previous file(s) with the same name. |
| 114 |
|
|
| 115 |
|
\item Packages are visited (and thus files discovered) {\it in the |
| 116 |
|
order that the packages are enabled} within \texttt{genmake2}. |
| 117 |
|
Thus, the files in \texttt{PackB} may superseed the files in |
| 118 |
|
\texttt{PackA} if \texttt{PackA} is enabled before |
| 119 |
|
\texttt{PackB}. Thus, package ordering can be significant! |
| 120 |
|
\end{enumerate} |
| 121 |
|
\end{enumerate} |
| 122 |
|
|
| 123 |
|
These rules were adopted since they provide a relatively simple means |
| 124 |
|
for rapidly including (or ``hiding'') existing files with modified |
| 125 |
|
versions. |
| 126 |
|
|
| 127 |
|
\subsubsection{Conditional Compilation and \texttt{PACKAGES\_CONFIG.h}} |
| 128 |
|
|
| 129 |
|
Given that packages are simply groups of files that may be added or |
| 130 |
|
removed to form a whole, one may wonder how linking (that is, FORTRAN |
| 131 |
|
symbol resolution) is handled. This is the second way that |
| 132 |
|
\texttt{genmake2} supports the concept of packages. Basically, |
| 133 |
|
\texttt{genmake2} creates a \texttt{Makefile} that, in turn, is able |
| 134 |
|
to create a file called \texttt{PACKAGES\_CONFIG.h} that contains a set |
| 135 |
|
of C pre-processor (or ``CPP'') directives such as: |
| 136 |
|
\begin{verbatim} |
| 137 |
|
#undef ALLOW_KPP |
| 138 |
|
#undef ALLOW_LAND |
| 139 |
|
... |
| 140 |
|
#define ALLOW_GENERIC_ADVDIFF |
| 141 |
|
#define ALLOW_MDSIO |
| 142 |
|
... |
| 143 |
|
\end{verbatim} |
| 144 |
|
These CPP symbols are then used throughout the code to conditionally |
| 145 |
|
isolate variable definitions, function calls, or any other code that |
| 146 |
|
depends upon the presence or absence of any particular package. |
| 147 |
|
|
| 148 |
|
An example illustrating the use of these defines is: |
| 149 |
|
\begin{verbatim} |
| 150 |
|
#ifdef ALLOW_GMREDI |
| 151 |
|
IF (useGMRedi) CALL GMREDI_CALC_DIFF( |
| 152 |
|
I bi,bj,iMin,iMax,jMin,jMax,K, |
| 153 |
|
I maskUp, |
| 154 |
|
O KappaRT,KappaRS, |
| 155 |
|
I myThid) |
| 156 |
|
#endif |
| 157 |
|
\end{verbatim} |
| 158 |
|
which is included from the file |
| 159 |
|
\filelink{calc\_diffusivity.F}{model-src-calc_diffusivity.F} |
| 160 |
|
|
| 161 |
|
There are some benefits to using this technique. The first is that |
| 162 |
|
code snippets or subroutines associated with packages can be placed or |
| 163 |
|
called from almost anywhere else within the code. The second benefit |
| 164 |
|
is related to the memory footprint and performance. Since unused code |
| 165 |
|
can be removed, there is no performance penalty due to unnecessary |
| 166 |
|
memory allocation or unused function calls. The major problems with |
| 167 |
|
this approach are difficult-to-read and difficult-to-test code caused |
| 168 |
|
by the numerous CPP statements. Developers should exerecise some |
| 169 |
|
discipline and avoid ``smearing'' implementation details across |
| 170 |
|
numerous files in a haphazard fashion. |
| 171 |
|
|
| 172 |
|
|
| 173 |
|
|
| 174 |
|
\subsection{Interfaces} |
| 175 |
|
|
| 176 |
|
|
Parent Directory
| 
Revision Log
| 
Revision Graph
| 
Patch