pthread, linked list with a double pointer

Question

I have finally got so far to create an accurate consumer-producer type model for some test application I am making but the last bit is causing me some problems.

I have 2 structs set-up for my application. One is used for a linked list which is used as a list of work that has to be done. The other one is a struct specific to each thread which contains a double pointer to the linked list. I don`t use a single pointer as then I am unable to modify the pointer in one thread and detect a change in the other.

//linked list struct:

typedef struct list_of_work list_of_work;
struct list_of_work {
    // information for the work 

    list_of_work        *next;

};

//thread struct:

typedef struct thread_specs {

    list_of_work         **linked_list;

    unsigned short       thread_id;

    pthread_mutex_t      *linked_list_mtx;

} thread_specs;

the double pointer in thread_specs get bound to a double pointer of the root of the list_of_work struct like so:

in main:

list_of_work                         *root;
list_of_work                         *traveller;
pthread_t                            thread1;
thread_specs                         thread1_info;

// allocating root and some other stuff
traveller = root;
thread1_info.linked_list = &traveller;

This all works without warnings or errors.

now I go on to create my pthread with:

pthread_create(&thread1, NULL, worker, &thread1_info )

and in my pthread I perform 2 casts, 1 to cast the thread_info struct and the other to cast the linked list. ptr is my argument:

thread_specs            *thread = (thread_specs *)ptr;
list_of_work            *work_list = (list_of_work *)thread->linked_list;
list_of_work            *temp;

this throws no errors.

I then have a function which is called list_of_work *get_work(list_of_work *ptr) , the function works so I won't post the entire thing but as you can see it expects to see a pointer to the linked list and it returns a pointer of the same linked list(which is either NULL or is the next piece of work).

So I use this function to get the next piece of work like this:

temp = get_work(*work_list);
if (temp != NULL) {
    work_list = &temp;
    printf("thread: %d || found work, printing type of work.... ",thread->thread_id);
}

Now this is the crux. How can I correctly cast and pass the pointer BEHIND the first pointer to my get_work() function so it can do what it does.

my compiler spits warnings:

recode.c:348:9: error: incompatible type for argument 1 of ‘get_work’
recode.c:169:14: note: expected ‘struct list_of_work *’ but argument is of type ‘list_of_work’

I thank whoever can hep me!

Answer 1

Based on the function get_work() 's definition you posted and error message, this issue here:

temp = get_work(work_list);
                ^
   /* Notice there's no dereferencing here */

The function expects a pointer to struct list_of_work whereas you pass a struct list_of_work .