c - Multiple threads writing on same file

Question

I would like to know if we can use multiple threads to write binary data on the same file.

FILE *fd = openfile("test");
int SIZE = 1000000000;
int * table = malloc(sizeof(int) * SIZE);
// .. filling the table
fwrite(table, sizeof(*table), SIZE, fd);

so I wonder if i can use threads,and each thread calls fssek to seek to a different location to write in the same file.

Any idea ?

Answer 1

fwrite should be thread safe, but you'll need a mutex anyway, because you need the seek and the write to be atomic. Depending on your platform, you might have a write function that takes an offset, or you might be able to open the file in each thread. A better option if you have everything in memory anyway as your code suggests, would just be for each thread to fill into a single large array and then write that out when everything is done.