Question

This is the code:

   unsigned int number;   FILE* urandom = fopen('/dev/urandom', 'r');   if (urandom) {     size_t bytes_read = fread(&number, 1, sizeof(number), urandom);     DCHECK(bytes_read == sizeof(number));     fclose(urandom);   } else {     NOTREACHED();   } 

If not, how do I make it thread-safe?

Answer 1

As long as each execution of the function is in its own thread (i.e., the local variables number, urandom, bytes_read are not shared between threads), I don’t see any thread-safety problems. Each thread will then have its own file descriptor into /dev/urandom. /dev/urandom can be opened simultaneously from multiple processes, so that’s okay.

By the way, /dev/urandom can fail to open, and your code should deal with it. Some causes are: running out of available file descriptors; /dev not properly mounted (although in this case you have bigger problems); your program is being run in a special chroot which denies access to any devices; etc.