sock_write
ret = sock_write(bp, str, n);
static int sock_write(BIO *h, const char *buf, int num);
.bwrite = sock_write,
CHECKr(pthread_create(&thread, &attr, sock_write, &fd));
CHECKr(pthread_create(&thread, NULL, sock_write, &fd));
while (sock_write(f))
int sock_write(struct sock *);