Blocking and Non-blocking Access


A system call can be blocking
If you want to read data but there is no data yet
If you want to write and there is no buffer space
Blocking calls can return EINTR
read(2) and write(2) can transfer only part of the data
read: if there is not enough data
write: if the buffer is small but not full
With fcntl(2) you can set O_NONBLOCK
read(2) will return EAGAIN instead of blocking

  flags = fcntl(fd, F_GETFL);
  fcntl(fd, F_SETFL, flags | O_NONBLOCK);