posix线程功能中的对象

Question

I have got a main function like this:

    int main(){
    ....
    Protocol SPI_conn;

    SPI_conn.omap_SPI_init();
    ....
    pthread_create(&rt_OneStep0_thread, NULL, rt_OneStep0, NULL);
    ....
    }

where SPI_conn is an object of the class Protocol and omap_SPI_init() is a method of the same class. My thread-function looks like this:

extern "C" void * rt_OneStep0(void *)
{   
while (1) {
  sem_wait(&step0_semaphore);
  SPI_do();
  sem_wait(&step0_semaphore);
  }
}

SPI_do() is also a function of the class Protocol. My question is, how can I use the object SPI_conn with the method SPI_do. Normally you can do it by reference, but here rt_OneStep0(void*) has to be defined like this, right?

I really appreciate your help!

Answer 1

Absolutely, your prototypes are correct. It all lies in how you can use the last parameter of pthread_create . It's actually a pointer to anything you want, that will be passed as the parameter to your thread's entry point (so, here, rt_OneStep0 ).

Hence, if you create your thread like this :

pthread_create(&rt_OneStep0_thread, NULL, rt_OneStep0, &SPI_conn);

You will receive the address of your SPI_conn object as the void* argument of your rt_OneStep0 function. You'll just have to cast it back to the proper type and you can then use it normally.

extern "C" void * rt_OneStep0(void *arg)
{
      Protocol *my_object = static_cast<Protocol*>(arg);   
      //... 
}

However, since you're dealing with threads and you'll be sharing an object created on your main thread, be careful about concurrency and race conditions.