Simplify platform abstraction

[elBoberido]

Brief feature description

Currently one needs to provide all headers for all platform, even if they are simply forwarding to the system header. This can be simplified by the C++17 feature __has_include

Detailed information

The platform would provide a generic implementation of the header. If the specific platform does not provide a custoom header, the generic one would be used.

This is an example for iceoryx_platform/include/iox/platform/semaphor.hpp

#ifndef IOX_PLATFORM_SEMAPHORE_HPP
#define IOX_PLATFORM_SEMAPHORE_HPP

#if __has_include("iox/platform/override/semaphore.hpp")
#include "iox/platform/override/semaphore.hpp"
#else
#include "iox/platform/generic/semaphore.hpp"
#endif // __has_include

#endif // IOX_PLATFORM_SEMAPHORE_HPP

The generic implementation in iceoryx_platform/generic/include/iox/platform/generic/semaphore.hpp would look like this

#ifndef IOX_PLATFORM_GENERIC_SEMAPHORE_HPP
#define IOX_PLATFORM_GENERIC_SEMAPHORE_HPP

#include <cstdint>
#include <semaphore.h>
#include <sys/types.h>

using iox_sem_t = sem_t;

#define IOX_SEM_FAILED SEM_FAILED
constexpr uint32_t IOX_SEM_VALUE_MAX = SEM_VALUE_MAX;

#ifndef IOX_PLATFORM_OVERRIDE_SEM_GETVALUE
inline int iox_sem_getvalue(iox_sem_t* sem, int* sval)
{
    return sem_getvalue(sem, sval);
}
#endif

#ifndef IOX_PLATFORM_OVERRIDE_SEM_POST
inline int iox_sem_post(iox_sem_t* sem)
{
    return sem_post(sem);
}
#endif

// ...

#ifndef IOX_PLATFORM_OVERRIDE_SEM_UNLINK
inline int iox_sem_unlink(const char* name)
{
    return sem_unlink(name);
}
#endif

#endif // IOX_PLATFORM_GENERIC_SEMAPHORE_HPP

For Linux, Unix, QNX and potentially other POSIX operating systems it would work out of the box.

FreeRTOS would specify a iceoryx_platform/freertos/include/iox/platform/override/semaphore.hpp header and partially reuse the generic header

#ifndef IOX_PLATFORM_FREERTOS_SEMAPHORE_HPP
#define IOX_PLATFORM_FREERTOS_SEMAPHORE_HPP

#define SEM_FAILED nullptr
#define IOX_PLATFORM_OVERRIDE_SEM_UNLINK

#include "iox/platform/generic/semaphore.hpp"

inline int iox_sem_unlink(const char*)
{
    // Named semaphores are not supported in FreeRTOS+POSIX
    configASSERT(false);
    return 0;
}

#endif // IOX_PLATFORM_FREERTOS_SEMAPHORE_HPP

Windows (and macOS) would have a full re-implementation in iceoryx_platform/windows/iox/platform/override/semaphore.hpp

#ifndef IOX_PLATFORM_WINDOWS_SEMAPHORE_HPP
#define IOX_PLATFORM_WINDOWS_SEMAPHORE_HPP

// fully custom implementation without using the generic header

#endif // IOX_PLATFORM_WINDOWS_SEMAPHORE_HPP

To use an out-of-tree platform one just needs to specify the path to iceoryx_platform/os/ like it is nowadays but it would be much simpler to add an maintain a platform which is mostly compatible with the generic platform.

Tasks

• [ ] Design document
• [ ] Implementation
• [ ] Update website/advanced/custom-iceoryx-platform.md

[elBoberido]

@budrus @elfenpiff @FerdinandSpitzschnueffler @mossmaurice @MatthiasKillat @dkroenke any objections to the proposed refactoring of the platform? It would be part of a 4.0 release and nothing in the short term but we might make it a prerequisite for Android support.