gimbal_tls.h

Go to the documentation of this file.

/*! \file
 *  \brief Thread-local variable management
 *  \ingroup core
 *
 *  This file provides a pair of macros serving as an abstraction layer
 *  between a platform's preferred thread-local storage mechanism, and
 *  the application.
 *
 *  Where supported, GBL_TLS() will use real, compiler-enabled static
 *  TLS by simply declaring the variable with the "thread_local" keyword
 *  and proceeding to access it normally.
 *
 *  If this preferred path is not available, using the same semantics, the
 *  back-end emulate this behavior by creating OS-level TLS storage using
 *  TinyCThread's C11 TLS API, which uses dynamically allocated storage
 *  and key-based lookups.
 *
 *   \author    2023 Falco Girgis
 *   \copyright MIT License
 */
 
#ifndef GIMBAL_TLS_H
#define GIMBAL_TLS_H
 
#include <tinycthread.h>
#include "../preprocessor/gimbal_compiler.h"
 
/*! \def GBL_TLS(type, name, init)
 *
 *  Defines a thread-local variable using the given information,
 *  and either using compiler or OS-level TLS depending on the
 *  platform.
 *
 *  \param type     variable type
 *  \param name     variable name
 *  \param init     variable initializer
 *
 *  \sa GBL_TLS_LOAD()
 */
#if !defined(GBL_PSP) && !GBL_TLS_EMULATED
#   define GBL_TLS(type, name, ...) GBL_THREAD_LOCAL type name = __VA_ARGS__
#else
#   define GBL_TLS(type, name, ...)
        tss_t name;
        static void tls_##name##_init_(void) {
            int res = tss_create(&name, free);
            GBL_ASSERT(res == thrd_success,
                       "Failed to create "#type" TLS for "#name);
        }
        static type* tls_##name##_load_(void) {
            static once_flag once = ONCE_FLAG_INIT;
            call_once(&once, tls_##name##_init_);
            type* pPtr = tss_get(name);
            if(!pPtr) {
                pPtr = malloc(sizeof(type));
                type temp = __VA_ARGS__;
                memcpy(pPtr, &temp, sizeof(type));
                const int res = tss_set(name, pPtr);
                GBL_ASSERT(res == thrd_success,
                           "Failed to set "#type" TLS for "#name);
            }
            return pPtr;
        }
#endif
 
/*! \def GBL_TLS_LOAD(name)
 *
 *  Fetches a pointer to a thread-local variable that was
 *  previously declared with GBL_TLS()
 *
 *  \param  name        variable name
 *  \return pointer     address of the given TLS variable
 *
 *  \sa GBL_TLS()
 */
#if !defined(GBL_PSP) && !GBL_TLS_EMULATED
#   define GBL_TLS_LOAD(name)    &name
#else
#   define GBL_TLS_LOAD(name)   tls_##name##_load_()
#endif
 
#endif // GIMBAL_TLS_H