libgg : Handy, portable wrappers for several basic OS features

LibGG provides a portable, unified interface to various very basic operating system features, making it easy to write portable programs without locking the author into a restricted, bloated, or overbearing development paradigm. By abstracting the most commonly used functionality in an operating-system-independent fashion, relying on prepackaged LibGG distributions can also can reduce the complexity involved in maintaining a portability suite (e.g. autotools) for the application's development.

Originally LibGG came into being as part of the GGI Project, when LibGII input functionality was separated from LibGGI into a stand-alone library, and a place was needed to put functions needed by both libraries. (Since then, we have forgotten what "GG" stood for, so don't ask.)

The master upstream source of LibGG is still distributed as part of LibGII, however it is itself a separately-distributable stand-alone package of utilities that can be very useful to applications developers.

LibGG provides the following groups of functions and/or macros. Some may not be possible to implement on some operating systems, some may be possible, just nobody has done so yet. We try to make them all available where we can find the time and expertise:

Time functions (ggCurTime(3), ggUSleep(3) and ggUSlumber(3)) to handle high-resolution timing and delays without busy-looping.

Cleanup callbacks (ggRegisterCleanup(3), ggUnregisterCleanup(3), ggCleanupForceExit(3)) to allow your application to perform emergency actions before a program is terminated abnormally.

Timer callbacks (ggAddTask(3), ggDelTask(3), ggTimeBase(3)) provide a (non-realtime) wall-clock periodic/one-shot callback scheduler that can be shared between many different areas of the application code without fear of interference.

Locking Functions (ggLock(3), ggLockCreate(3), ggLockDestroy(3), ggTryLock(3), ggUnlock(3)) which are thread-safe in threaded environments.

System and CPU detection utilities (ggGetSwarType(3), GG_HAVE_INT64, GG_LITTLE_ENDIAN) to allow you to detect CPU endianness and the presence of features such as SWAR (SIMD) instruction sets (e.g. MMX), and to turn on/off or change SWARs for testing or as a workaround.

Very basic overrun-proof string operations (ggstrlcpy(3), ggstrlcat(3)) which are a horrible mess for cross-platform programs to map to OS-local string functions/headers.

Pluggable module management functions (ggLoadModule(3), ggMLoadModule, ggGetSymbolAddress(3), ggFreeModule(3)) that allow you to create a plug-in system where code is dynamically loaded into and out of your program. (Support for statically linked emulation for embedded systems is also provided.)

An option parser (ggParseOpts, ggSystemOpts) and plugin configuration system (ggGetUserDir(3), ggParseTarget, ggLoadConfig, ggFreeConfig, ggMatchConfig, ggConfigExpandAlias) which are by-products of the pluggable module support but can be useful for other things if you like the format.

LibGG uses the environment variable $GG_OPTS, and expects it to contain a valid option string as documented in the manpage for ggParseOpts. The available options are documented along with the LibGG API functions which they most affect.

LibGG requires the exclusive use of one signal under certain environments. This signal defaults to SIGPROF, where available, but may be configured through the GG_OPTS option "-signum=n" where n represents the numerical value of the signal to use. This signal should not be one of the fatal signals handled by the LibGG cleanup facilities, and must be a signal onto which a handler may be assigned. Applications should not install handlers or alter the signal handler in any way for this signal.

There is still some legacy to LibGGI in some of the namespace, especially GGI_LITTLE_ENDIAN is currently the real name for GG_LITTLE_ENDIAN, which is an unofficial new addition destined to replace it. Deprecation will take a few revisions as it must be done in an orderly fashion.

Likewise the header file is included as <ggi/gg.h> but we will probably keep that as-is because of the way LibGG is distributed and to avoid adding more clutter in system include directories than is necessary.

Several features are incomplete, for example, code is still needed to detect SWAR on many of the more obscure architectures.