Source code =========== Code style ---------- We intentionally do not have too many code conventions in the PMIx code base. All languages ^^^^^^^^^^^^^ * 4 space tabs. No more, no less. * **NEVER** use actual tab characters; always use spaces. Both emacs and vim have secret mojo that can automatically use spaces when you hit the ```` key. This makes the code look the same in every browser, regardless of individual tab display settings. C / C++ ^^^^^^^ * When comparing constants for equality or inequality, always put the constant on the left. This is defensive programming: if you have a typo in the test and miss a ``!`` or ``=``, you'll get a compiler error. For example: .. code-block:: c /* Do this */ if (NULL == foo) { ... } /* Because if you have a typo (i.e., = instead of ==), this will be a compile error rather than a subtle bug */ if (NULL = foo) { ... } * More defensive programming: *always* include blocks in curly braces ``{ }``, even if they are only one line long. For example: .. code-block:: c /* Do this */ if (whatever) { return OMPI_SUCCESS; } /* Not this */ if (whatever) return OMPI_SUCCESS; * PMIx requires a C99-compliant compiler. * C++-style comments are now allowed (and preferred). * C99-style mixing declarations are allow allowable (and preferred). * **ALWAYS** include ``pmix_config.h`` as your first #include file. There are very, very few cases where this is not true (E.g., some bizarre Windows scenarios). But in 99.9999% of cases, this file should be included **first** so that it can affect system-level #include files if necessary. * Filenames and symbols must follow the **prefix rule** (see [e-mail thread](http://www.open-mpi.org/community/lists/devel/2009/07/6389.php)): * Filenames must be prefixed with ``_``. * Public symbols must be prefixed in components with ``pmix__``. When in doubt about whether a symbol is public, be safe and add the prefix. * Non-public symbols must be declared ``static`` or otherwise made to not appear in the global scope. * **ALWAYS** #define macros, even for logical values. * The GNU Way is to ``#define`` a macro when it is "true" and to ``#undef`` it when it is "false". * In PMIx, we **always** ``#define`` a logical macro to be either 0 or 1 -- we never ``#undef`` it. * The reason for this is defensive programming: if you are only checking if a preprocessor macro is defined (via ``#ifdef FOO`` or ``#if defined(FOO)``), you will get no warning when compiling if you accidentally misspell the macro name. However, if you use the logic test ``#if FOO`` with an undefined macro (e.g., because you misspelled it), you'll get a compiler warning or error. .. admonition:: Rationale :class: tip Misspelled macro names can be tremendously difficult to find when they are buried in thousands of lines of code; we will take all the help from the preprocessor/compiler that we can get! .. code-block:: c /* GNU Way - you will get no warning from the compiler if you misspell "FOO"; the test will simply be false */ #ifdef FOO ... #else ... #endif /* PMIx Way - you will get a warning from the compiler if you misspell "FOO"; the result of the test is a different value than whether you spelled the macro name right or not */ #if FOO ... #else ... #endif Shell scripting ^^^^^^^^^^^^^^^ Please read some of the existing shell code in the source code tree and try to use a similar style. * Always enclose evaluated shell variables in quotes to ensure that multi-token values are handled properly. .. code-block:: sh # This is bad if test $foo = bar; then # This is good if test "$foo" = "bar"; then * The one exception to this is that when doing an assignment to a shell variable from another shell variable, it is not necessary to use quotes on the right hand side: .. code-block:: sh # This is harmless, but unnecessary foo="$bar" # This is actually sufficient, even for multi-token values of $bar foo=$bar * Do not use the ``==`` operator for ``test`` |mdash| this is a GNU extension and can cause portability problems on BSD systems. Instead, use the single ``=`` operator. .. code-block:: sh # This is bad if test "$foo" == "bar"; then # This is good if test "$foo" = "bar"; then m4 ^^^ We do not have specific coding style guidelines for m4 (the language used to create the ``configure`` script). Please read some of the existing m4 code in the source code tree and try to use a similar style. Tree layout ----------- There are a few notable top-level directories in the source tree: * The main PMIx source is under the ``src`` directory * ``config``: M4 scripts supporting the top-level ``configure`` script * ``etc``: Some miscellaneous text files * ``docs``: Source code for PMIx documentation * ``examples``: Trivial example programs * ``include``: The public PMIx headers The ``src`` directory generates a top-level library named ``libpmix``. It can be built as either a static or shared library. The directory structure under it includes: * ``class``: C++-like "classes" (using the OPAL class system) specific to this project * ``include``: Top-level internal include files * ``mca``: MCA frameworks and components specific to PMIx * ``runtime``: Startup and shutdown of PMIx at runtime * ``tools``: Executables specific to PMIx * ``util``: Random utility code The layout of the ``mca`` tree is strictly defined to be of the form: .. code-block:: text mca/FRAMEWORK/COMPONENT To be explicit: it is forbidden to have a directory under the ``mca`` tree that does not meet this template (with the exception of ``base`` directories, explained below). Hence, only framework and component code can be in the ``mca`` tree. That is, framework and component names must be valid directory names (and C variables; more on that later). For example, the CLIENT PTL component is located in ``mca/ptl/client/``. The name ``base`` is reserved; there cannot be a framework or component named ``base``. Directories named ``base`` are reserved for the implementation of the MCA and frameworks. Here are a few examples (as of the |opmix_series| source tree): .. code-block:: sh # Main implementation of the MCA mca/base # Implementation of the ptl framework mca/ptl/base # Implementation of the client component of the ptl framework mca/ptl/client Under these mandated directories, frameworks and/or components may have arbitrary directory structures, however. Symbol Visibility ----------------- The ``PMIX_EXPORT`` macro provides a method to annotate symbols to indicate their intended visibility when compiling dynamically shared object files (e.g., ``libpmix.so``). The macro expands to the appropriate compiler and platform flags for marking whether a symbol should be explicitly made public in the PMIx library namespace. The ``PMIX_EXPORT`` attribute is used to declare that a symbol is to be visible outside of the PMIx DSO's scope. .. note:: This is entirely related to dynamic library compilation and does not apply to static compilation.