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GeneralPortability
This page contains a number of general notes on writing code in Open MPI such that it has the best chance of "Just Working" on as many platforms as possible. There will likely still be problems, but this should help :).
Some links for writing portable code:
- The Autoconf Manual's C Function Portability Guide
- The Autoconf Manual's Header Portability Guide
- Using printf()
Some links for writing portable configure mojo:
On traditional Unix systems, environ is accessed by adding extern char** environ somewhere in the file, and accessing it as a char** (when getenv() / setenv() won't do the job, of course). On OS X, environ exists in crt0.o instead of libc.so, which means that it is an undefined symbol that is not resolvable until the link of the application. This causes significant problems for users that are building shared libraries that depend upon Open MPI's shared libraries. There is an accessor function that works around this problem. This means that environ should be declared something like:
#ifdef HAVE_CRT_EXTERNS_H
#include <crt_externs.h>
#endif
#if defined(__WINDOWS__)
#ifdef HAVE__NSGETENVIRON
#define environ (*_NSGetEnviron())
#else
OPAL_DECLSPEC extern char **environ;
#endif
#endif /* defined(__WINDOWS__) */This should be done automatically by including opal/util/opal_environ.h in any files that require access to environ. This also means that environ is a preprocessor define on OS X, so it can not be used as a variable or function name anywhere in the source code that may include opal_environ.h.
All header files should be properly secured against multiple inclusion, i.e.:
#ifndef OPAL_MCA_MYNAME_H
#define OPAL_MCA_MYNAME_H
...
#endif /* OPAL_MCA_MYNAME_H */
All header files should be C++ safe, i.e. they should be ready to be included from C++ source code. For this the BEGIN_C_DECLS and END_C_DECLS macros (defined in opal/include/opal_config_bottom.h is provided to mark the beginning of the C declarations. These are equivalent to the corresponding extern "C" { declarations.
Any system header file, that is not required by Posix should be checked for with configure and ifdef'd in the header file.
The header files currently checked by configure can be greped for with grep HAVE_ opal/include/opal_config.h.in | grep -e '_H$'.
A particular nice header file is stdbool.h, which provides the bool datatype -- however, this of course should be not included in standard-conforming C++ code.
Therefore, this inclusion should be protected:
#if defined(HAVE_STDBOOL_H) && !(defined(c_plusplus) || defined(__cplusplus))
#include <stdbool.h>
#endif