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c++ - Interoperabilty between C and C++ atomics

问题描述

Suppose, I have a task that might be cancelled from another thread. The task is performed in a C function, another thread runs C++ code. How do I do that?

Rough example.

C:

void do_task(atomic_bool const *cancelled);

C++:

std::atomic_bool cancelled;
…
do_task(&cancelled);

For now, I created a file atomics.h with the following content:

#ifdef __cplusplus
#include <atomic>
using std::atomic_bool;
#else
#include <stdatomic.h>
#endif

It appears to work, but I don't see any guarantees for that. I wonder, if there is a better (correct) way.

标签： c++catomic

解决方案

To side-step all ABI issues you may like to implement a C function that is called from C++ and operates on that atomic_bool. This way your C++ code doesn't need to know anything about that global variable and its type:

In an .hfile:

#ifdef __cplusplus
extern "C" {
#endif

void cancel_my_thread(void);
int is_my_thread_cancelled(void);

#ifdef __cplusplus
}
#endif

And then in a .c file:

#include <stdatomic.h>

static atomic_bool cancelled = 0;

void cancel_my_thread(void) {
    atomic_store_explicit(&cancelled, 1, memory_order_relaxed);
}
int is_my_thread_cancelled(void) {
    return atomic_load_explicit(&cancelled, memory_order_relaxed);
}

The C++ code would include that headed and call cancel_my_thread.

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