C++, create a pthread for a function with a return type?

Question

Say I have the following function:

bool foo (int a); // This method declaration can not be changed.

How do I create a pthread for this? And how

Answer 1

You could encapsulate the function you want to invoke in a function object, and then invoke that function object from within your pthread function:

First, define a function object that encapsulates your function call.

struct foo_functor {
    // Construct the object with your parameters
    foo_functor(int a) : ret_(), a_(a) {}

    // Invoke your function, capturing any return values.
    void operator()() {
        ret_ = foo(a_);
    }

    // Access the return value.
    bool result() {
        return ret_;
    }

private:
    bool ret_;
    int a_;
};

Second, define a function with the appropriate pthread signature that will invoke your function object.

// The wrapper function to call from pthread. This will in turn call 
extern "C" {
    void* thread_func(void* arg) {
        foo_functor* f = reinterpret_cast(arg);
        (*f)();
        return 0;
    }
}

Finally, instantiate your function object, and pass it as a parameter to the thread_func function.

foo_functor func(10);

pthread_t pid;
pthread_create(&pid, NULL, thread_func, &func);
pthread_join(pid, NULL);

bool ret = func.result();