2. SystemUid

2. semaphore rather than dispatch_semaphore for tsem_xxx
3. fail-fast comments
4. niche

2. tsem_xxx for mac

2. for the sake of SIGALRM used in the base code, add taos_block_sigalrm and so forth
3. TODO: getaddrinfo would block a few unnecessary seconds when host ~ *.local
         better give warning/suggestion message to user, or just bypass getaddrinfo
         and fail the function

2. initial port of taosd for MacOSX