Passing struct pointer als parameter for pthread function - linux

Question

Hello I'm fallowing a tutorial for pthreading, but something went wrong down the road since can't make the reference to my struct passable by
pthread_create(...,(void* stuctName)) , I'm looking for some advices or fixes since I have no idea where or what I messed up...
code:
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#include <math.h>
struct dataBlock{
struct node *root;
int listSize;
int forIndex;
};
struct node { // std linked list node
int value;
int worker;
struct node *next;
};
int slots = 3; // only 3 threads are allowed to access the list
int availableCheck(){ // check if thread can acces the list
if(slots < 3) return 0;
else return -1;
}
pthread_mutex_t mutp = PTHREAD_MUTEX_INITIALIZER; //condvar mutex
pthread_cond_t condvar = PTHREAD_COND_INITIALIZER; //condvar
void * worker( void *data ){ //WORKER FUNCTION
printf( "* Thread start: ^\n");
struct dataBlock *inData = (struct dataBlock *) data;
struct node *root = data->root;
int listSize = data->listSize;
int forIndex = data ->forIndex;
// printf( " * I am %li _ worker # %li : \n", forIndex, pthread_self() );
pthread_mutex_lock( &mutp );
if(availableCheck() < 0){
printf( " ^^^ List not available yet... \n" );
pthread_cond_wait( &condvar, &mutp );
}
// printf( "* Got data: %lu \n", index );
pthread_cond_signal( &condvar ); //
pthread_mutex_unlock( &mutp );
return NULL;
}
int main( int argc, char *argv[] ){
if ( argc != 3 ){
printf( "Programm must be called with \n NR of elements and NR of workers! \n " );
exit( 1 );
int i;
struct node *root;
struct node *iterator;
//prepare list for task
int listSize = atoi(argv[1]);
int nrWorkers = atoi(argv[2]);
root = malloc(sizeof( struct node) );
root->value = rand() % 100;
root->worker = 0;
iterator = root;
for( i=1; i<listSize; i++ ){
iterator->next = malloc(sizeof(struct node));
iterator = iterator->next;
iterator->value = rand() % 100;
iterator->worker = i % nrWorkers;
printf("node #%d worker: %d value: %d\n", i, iterator->worker,iterator->value);
}
// Create all threads to parse the link list
int ret, *id;
printf("workersInput: %d\n",nrWorkers);
pthread_t w_thread;
pthread_t* w_threads = malloc(nrWorkers * sizeof(w_thread));
struct dataBlock *data = malloc(sizeof(struct dataBlock));
data->root = root;
data->listSize = listSize;
for( i=0; i < nrWorkers; i++ ){ // CREATING THREADS
data->forIndex = i;
ret = pthread_create ( &w_threads[i], NULL, worker, (void *) data );
if( ret ) {
perror("Thread creation fail");
exit(2);
}
}
for ( i = 0; i < nrWorkers; i++){
pthread_join(w_threads[i],NULL);
}
free(root);
free(iterator);
return 0;
}
Compiling(Wall flag)
s.c: In function ‘worker’:
s.c:32:26: warning: dereferencing ‘void *’ pointer [enabled by default]
s.c:32:26: error: request for member ‘root’ in something not a structure or union
s.c:33:22: warning: dereferencing ‘void *’ pointer [enabled by default]
s.c:33:22: error: request for member ‘listSize’ in something not a structure or union
s.c:34:22: warning: dereferencing ‘void *’ pointer [enabled by default]
s.c:34:22: error: request for member ‘forIndex’ in something not a structure or union
s.c:34:6: warning: unused variable ‘forIndex’ [-Wunused-variable]
s.c:33:6: warning: unused variable ‘listSize’ [-Wunused-variable]
s.c:32:15: warning: unused variable ‘root’ [-Wunused-variable]
s.c:31:20: warning: unused variable ‘inData’ [-Wunused-variable]
s.c: In function ‘main’:
s.c:81:12: warning: variable ‘id’ set but not used [-Wunused-but-set-variable]

Answer 1

Use inData->root instead of data->root etc... (or cast explicitly always your data) since data is a void* pointer, that is a pointer to some unspecified data type.