Pass a structure with an array to multiple threads
I was desperately trying to pass the structure to multiple threads. The problem is that I cannot find the correct format to pass it to the pthread_create function. It just won't work. If you tried to pass my struct pointers to pthread_create but it just won't work. I have pointer assignment errors.
typedef struct thread{
pthread_t thread_id;
char *filename;
int blocksize;
int random_int;
} ThreadData;
int main(int argc, char *argv[]) {
int nb_threads = atoi(argv[3]);
int blocksize = atoi(argv[2]);
int re;
int index;
char *name;
char* mode = argv[1];
int i = 0;
ThreadData thread[nb_threads];
int random_int;
srand(time(NULL));
random_int = rand();
index = detect_mode(mode);
index_glob = index;
for(i=0; i < nb_threads; i++){
snprintf(name, 25,"temp%d",i);
thread[i].filename = name;
thread[i].blocksize = blocksize;
thread[i].random_int = random_int;
switch(index_glob){
case 0:
re = pthread_create(&(thread[i].thread_id),NULL,write_seq_file,(void *)(&thread[i]));
break;
case 1:
re = pthread_create(&(thread[i].thread_id),NULL,write_ran_file,(void *)(&thread[i]));
break;
case 2:
re = pthread_create(&(thread[i].thread_id),NULL,read_seq_file,(void *)(&thread[i]));
break;
case 3:
re = pthread_create(&(thread[i].thread_id),NULL,read_ran_file,(void *)(&thread[i]));
break;
default:
exit(0);
break;
}
if(re == -1){
printf("Error creating thread %d / %d\n",(i+1),nb_threads);
}
else{
printf("Thread %d / %d created.\n",(i+1),nb_threads);
}
}
for(i=0; i< nb_threads; i++){
pthread_join(thread[i].thread_id, NULL);
}
return 0;
}
void* write_seq_file(void *thread){
ThreadData *my_data = (ThreadData*)thread;
char *filename = my_data->filename;
FILE* fp = fopen(filename,"w+");
int blocksize = my_data->blocksize;
char c = 'a';
long i;
for (i=0; i<blocksize; i++){
fputc(c,fp);
}
pthread_exit(NULL);
}
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I didn't quite understand your program and I'm not sure if this will work as you expect. But
Here are some points that can be compiled:
pthread_create expects void * (* start_routine) (void *) as a working function. Therefore, change the write_seq_file and all working functions to the following format.
void* write_seq(void *thread)
{
...
return NULL;
}
Your Thread data array is an array of objects. Not pointers. So first get the address and throw it into the void.
re = pthread_create(&(thread[i].thread_id),NULL,write_seq_file,(void *)(&(thread[i])));
Not sure if exiting (0) in the middle is a good idea. I would rather use return 0; because the main function needs to return a value.
This code does not declare the following. So hopefully there are no problems there.
index = detect_mode(mode);
index_glob = index;
Make sure you have function prototypes declared before main, or move the function implementation above the main function.
Finally, pthread_join expects the pthread_t thread to be the first argument. Where the line needs to be changed as shown below.
pthread_join(thread[i].thread_id, NULL);
Hope it helps.
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