将结构作为值参数传递给线程

Question

I want to create more than one thread with a vector of threads and I'm trying to pass a struct with values that are changing with every call. The problem is I don't want to pass the struct as a memory location with &, because every thread receives a different value of the struct. I want to pass the struct as a value parameter. When I try, the gcc compiler throws an error: Violation segment ( `core 'generated). Here is part of my code:

//the struct
struct intervalos{
  int from;
  int to;
  int number;
};


// the calls
for (int i = 0; i<=num ; i++){
    struct intervalos *inter;

    /*re asign the values of the struct...*/

    pthread_create( &vector[i], NULL, fun, inter);
}


//function of threads
void* fun(void* data) {
    struct intervalos *inter = data ;
    /* do something else */
}

Answer 1

You could allocate the data on the heap one of the functions in the malloc family. The caller of pthread_create would not free the allocated memory, instead the new thread would do it, after it is done with processing the data (which could be after initial processing or just before thread exit, depending on what the thread does).

The fact that you can pass heap pointers between threads in this way makes malloc considerably more complicated, so you might as well use this functionality.

Answer 2

You are not initializing your inter variable, thus causing the program to throw a segfault. Normally, you will have to use calls like malloc() to allocate memory for it before passing the pointer to any other function.

Alternatively, if you insist that you pass an unallocated pointer to the pthread_create function, you can pass along a reference to the pointer, ie pthread_create(&vector[i], NULL, fun, &inter) , and then use *inter = malloc(sizeof(struct intervalos)) to allocate memory for it within each thread.

Answer 3

You can only pass a pointer to a pthread_t , so you cannot pass data by value, only by reference.

struct intervalos * inter = malloc(sizeof(intervalos));
if (!inner) {
    // Handle out of memory error
}
inter->from = ...;
inter->to = ...;
inter->number = ...;

int error = pthread_create(&vector[i], NULL, fun, inter);
if (error) {
    // Thread was not created.
    // Free allocation to not leak memory.
    free(inner);
    // Handle cannot create thread error
}

And in the thread:

void * fun ( void * data ) {
    struct intervalos * inter = data ;

    // ... Do whatever you want ...

    // Once done, free allocation or you'll leak memory
    free(inter);
    return NULL;
}