libdpf/thirdparty/portable-snippets/atomic/README.md

Atomic Operations

This header provides atomic operations in a way which is portable to most platforms. Current back-ends include:

• C11
• GCC-style _atomic* builtins
• Old-style GCC sync_* builtins
• clang-style _c11_atomic* builtins
• MSVC-style Interlocked* intrinsics
• OpenMP (using critical sections; there is no atomic CAS)

This is sufficient to support most modern, actively developed compilers. PGI C/C++ Compiler, which doesn't currently support atomics but hopefully will soon, in the meantime you can use the OpenMP backend (just pass -mp to the compiler).

Most things are implemented with the preprocessor, but if they were functions the prototypes (the 64-bit versions, just s/64/32/ for the 32-bit versions) would loo like:

psnip_int64_t psnip_atomic_int64_load(
  psnip_atomic_int64* object);

void psnip_atomic_int64_store(
  psnip_atomic_int64* object,
  psnip_int64_t desired);

_Bool psnip_atomic_int64_compare_exchange(
  psnip_atomic_int64* object,
  psnip_int64_t* expected,
  psnip_int64_t desired);

psnip_nonatomic_int64 psnip_atomic_int64_add(
  psnip_atomic_int64* object,
  psnip_int64_t operand);

psnip_nonatomic_int64 psnip_atomic_int64_sub(
  psnip_atomic_int64* object,
  psnip_int64_t operand);

If no atomics are supported, PSNIP_ATOMIC_NOT_FOUND will be defined; you'll probably have to use locks (if you want a portable API for that you may be interested in TinyCThread), or you could try the atomic_ops package.

Dependencies

To maximize portability you should #include the exact-int module before including atomic.h, but if you don't want to add the extra file to your project you can omit it and this module will simply rely on <stdint.h>. As an alternative you may define psnip_int32_t, and psnip_int64_t to appropriate values yourself before including atomic.h.