File Descriptors Opened by Crystal at Initialization

On Unix-like systems, at initialization, Crystal opens:

• A copy of each of stdin, stdout, and stderr if these are terminal devices. These would appear as file descriptors 3, 4, and 5 if all of stdin, stdout, and stderr are connected to a terminal.
• Both ends of two pipes, for a total of 4 file descriptors. These are a kludge for signal handling. Since few libc functions are safe to call in a signal handler, Crystal catches signals, and writes to a pipe an indication that the signal was caught. Crystal's main select() or poll() loop will wake up on the pipe and receive that notification, and activate the user's signal handler.
• One file descriptor used by eventpoll.