C++ constructor guards for static instances

C++ constructor guards for thread-safe initialization of static instances.

C++ constructor guards for thread-safe initialization of static instances.

Warning

This implementation is likely only compatible with g++

Introduction

The libstd++ ABI requires implementations of the following functions:

int __cxa_guard_acquire(__guard *g);
void __cxa_guard_release(__guard *g);
void __cxa_guard_abort(__guard *g);

These functions are not intended to be ever used by the programmer, instead the C++ compiler will emit code calling them if statically allocated class instances are used. In a multi-threaded environment special care needs to be taken to prevent race conditions while initializing and using such instances. This modules provides them.

Usage

This module is intended to be used by platforms that want to provide C++ support, but the used standard C++ library does not provide these guards. In this case, adding this module will do the trick. The programmer / user should never interact with any of the functions.

Note that on some platforms the type __guard is defined differently from the "generic" definition, most notably ARM. For those platforms a header named cxx_ctor_guards_arch.h needs to be created containing the correct typedef and the preprocessor macro CXX_CTOR_GUARDS_CUSTOM_TYPE needs to be defined.

Implementation

This implementation provides the C++ ctor guards as defined by the libstd++ ABI used in g++. It will likely not be compatible with other implementations of libstd++.

The libstd++ ABI expects the functions to be implemented as C functions. Most implementations will put the code into C++ files and wrap everything into an extern "C" {...}. This implementation will just use a plain C file for less boilerplate.

The implementation intentionally makes only use of a single byte of the __guard type. This should result in the implementation being usable on any platform, regardless of the actual size of __guard.