[Olena-patches] olena-2.0-106-gde2cb23 doc/tutorial.tex: Add section about multifile compilation.

--- milena/ChangeLog | 4 + milena/doc/tutorial.tex | 159 +++++++++++++++++++++++++++++++++++++++------- 2 files changed, 138 insertions(+), 25 deletions(-) diff --git a/milena/ChangeLog b/milena/ChangeLog index 4a14115..ce8608c 100644 --- a/milena/ChangeLog +++ b/milena/ChangeLog @@ -1,3 +1,7 @@ +2012-06-18 Guillaume Lazzara &lt;z(a)lrde.epita.fr&gt; + + * doc/tutorial.tex: Add section about multifile compilation. + 2012-05-23 Guillaume Lazzara &lt;z(a)lrde.epita.fr&gt; Fix a bug in a tutorial example. diff --git a/milena/doc/tutorial.tex b/milena/doc/tutorial.tex index 8fee888..e67a9da 100644 --- a/milena/doc/tutorial.tex +++ b/milena/doc/tutorial.tex @@ -952,34 +952,141 @@ result. \doxysubsection{tuto3howtocompile}{Include path} -If Milena has been installed in a custom directory, e.g. not /usr/include or -/usr/local/include, the path to the library headers must be passed to the -compiler. +If Milena has been installed in a custom directory, e.g. not +/usr/include or /usr/local/include, the path to the library headers +must be passed to the compiler. With g++ and MinGW, the option is \B{-I$<$path$>$}. \begin{verbatim} $ g++ -Ipath/to/mln my_program.cc \end{verbatim} -For other compilers, please look at the documentation and search for ``include -path''. - +For other compilers, please look at the documentation and search for +``include path''. \doxysubsection{tuto3liblink}{Library linking} -As it is usually expected when using a library, no library linking is needed for -the library itself. -Milena is a ``header only'' library and is compiled ``on demand'' with your -program. +As it is usually expected when using a library, no library linking is +needed for the library itself. Milena is a ``header only'' library +and is compiled ``on demand'' with your program. + +If you use specific input/output you may need to link your program +with the right graphic library. For more information, please refer to +section \doxyref{inputoutput} in the Quick Reference Guide. + + +\doxysubsection{tuto3multifile}{Multifile Compilation} + +In some cases, one might want to use Olena in a more complex program +compiled through several independant files. + +Let's consider the program is composed of two files both including +Milena headers: +\begin{itemize} + \item main.cc + \item task.cc +\end{itemize} + +Content of main.cc +\begin{verbatim} +#include <mln/core/image/image2d.hh> + +// Main.cc -If you use specific input/output you may need to link your program with the -right graphic library. For more information, please refer to section -\doxyref{inputoutput} in the Quick Reference Guide. +// Forward declaration. +void f(); + +int main() +{ + mln::image2d<int> ima; +} +\end{verbatim} + +Content of task.cc +\begin{verbatim} +#include <mln/core/image/image2d.hh> + +// task.cc + +void f() +{ + mln::image2d<int> ima; +} + +\end{verbatim} + +The following call to the compiler will fail: +\begin{verbatim} +$ g++ -Ipath/to/mln main.cc task.cc +/tmp/ccRaVKO2.o:(.data+0x0): multiple definition of `mln::trace::quiet' +/tmp/ccAArtQl.o:(.data+0x0): first defined here +/tmp/ccRaVKO2.o:(.bss+0x0): multiple definition of `mln::trace::tab' +/tmp/ccAArtQl.o:(.bss+0x0): first defined here +/tmp/ccRaVKO2.o:(.bss+0x4): multiple definition of `mln::trace::full_trace' +/tmp/ccAArtQl.o:(.bss+0x4): first defined here +/tmp/ccRaVKO2.o:(.bss+0x8): multiple definition of `mln::trace::internal::max_tab' +[...] +collect2: ld returned 1 exit status +\end{verbatim} + +This issue is due to the ``header only'' architecture of the library +and to global variables. global variable symbols are compiled for each +files and it leads to symbols conflicts. + +The solution is to force the compiler to compile these symbols only +once. Olena provided a mechanism to do this. + +In one of the files including olena headers, at the very top of +the file (before any includes), add the following line: +\begin{verbatim} +#undef MLN_WO_GLOBAL_VARS +\end{verbatim} + +For instance, we would have in main.cc: +\begin{verbatim} +#undef MLN_WO_GLOBAL_VARS +#include <mln/core/image/image2d.hh> + +// Main.cc + +// Forward declaration. +void f(); + +int main() +{ + f(); +} + +\end{verbatim} + +The compile the sources again with the define: +\begin{verbatim} +$ g++ -DMLN_WO_GLOBAL_VARS -Ipath/to/mln main.cc task.cc +\end{verbatim} + +The previous duplicate symbols will then be compiled thanks to main.cc +which force the effective declaration of the global symbols. Because +of the default define at compile time, any .cc files including headers +from the library will just declare but not define global symbols. + +For that reason, sometimes one may also encounter the following error +after defining MLN\_WO\_GLOBAL\_VARS. +\begin{verbatim} +g++ -DMLN_WO_GLOBAL_VARS -I$PWD/milena/ main.cc task.cc +/tmp/cc4Ys1xX.o: In function `f()': +task.cc:(.text+0x6): undefined reference to `mln::border::thickness' +collect2: ld returned 1 exit status +\end{verbatim} +In our case, it would be because task.cc includes and uses global +symbols which are not included in main.cc. Therefore, they are defined +but never compiled. Here, the file main.cc should include the +corresponding headers. \doxysubsection{tuto3compildndebug}{Disable Debug} -By default, Olena enables a lot of internal pre and post conditions. Usually, -this is a useful feature and it should be enabled. It can heavily slow down a -program though and these tests can be disabled by compiling using -DNDEBUG: +By default, Olena enables a lot of internal pre and post +conditions. Usually, this is a useful feature and it should be +enabled. It can heavily slow down a program though and these tests can +be disabled by compiling using -DNDEBUG: \begin{verbatim} $ g++ -DNDEBUG -Ipath/to/mln my_program.cc @@ -987,20 +1094,22 @@ $ g++ -DNDEBUG -Ipath/to/mln my_program.cc \doxysubsection{tuto3compoptimflags}{Compiler optimization flags} -In this section you will find remarks about the compiler optimization flags and -their impact on the compilation and execution time. +In this section you will find remarks about the compiler optimization +flags and their impact on the compilation and execution time. \doxysubsubsection{tuto3compoptimgcc}{GCC} \begin{itemize} - \item \B{-O0}, combined with -DNDEBUG, it leads to the fastest compilation - time. The execution is somewhat slow though since dispatch functions and one - line members are not inlined by the compiler. - \item \B{-O1}, best compromise between compilation time and execution time. - \item \B{-O2}, \B{-O3}, combined with -DNDEBUG, it leads to the best execution - time. However these optimizations dramatically slow down the compilation and - requires much more memory at compile time. + \item \B{-O0}, combined with -DNDEBUG, it leads to the fastest + compilation time. The execution is somewhat slow though since + dispatch functions and one line members are not inlined by the + compiler. + \item \B{-O1}, best compromise between compilation time and + execution time. + \item \B{-O2}, \B{-O3}, combined with -DNDEBUG, it leads to the best + execution time. However these optimizations dramatically slow down + the compilation and requires much more memory at compile time. \end{itemize} \doxysubsubsection{tuto3compoptimother}{Other compilers} -- 1.7.2.5