whether rand_r is real thread safe?
- by terry
Well, rand_r function is supposed to be a thread safe function. However, by its implementation, I cannot believe it could make itself not change by other threads.
Suppose that two threads will invoke rand_r in the same time with the same variable seed.
So read-write race will occur.
The code rand_r implemented by glibc is listed below. Anybody knows why rand_r is called thread safe?
int
rand_r (unsigned int *seed)
{
unsigned int next = *seed;
int result;
next *= 1103515245;
next += 12345;
result = (unsigned int) (next / 65536) % 2048;
next *= 1103515245;
next += 12345;
result <<= 10;
result ^= (unsigned int) (next / 65536) % 1024;
next *= 1103515245;
next += 12345;
result <<= 10;
result ^= (unsigned int) (next / 65536) % 1024;
*seed = next;
return result;
}
