What requirements should be considered when using a descriptor in non-blocking mode?

When using a descriptor (for example, a file descriptor) in non-blocking mode, the following requirements must be considered:

• Error handling for EAGAIN/EWOULDBLOCK: when attempting to read or write, if the operation cannot be completed immediately, the system returns an error EAGAIN or EWOULDBLOCK. The program should handle these cases correctly, for example, by retrying later.

• Use of notification mechanisms: to efficiently work with non-blocking descriptors, mechanisms like select(), poll(), epoll(), or similar are often used to determine when the descriptor is ready for reading or writing.

• Proper state management: it is necessary to consider that operations may be partially completed (for example, not all data is written), so it is important to correctly track the number of bytes processed and continue operations.

• Initialization of the descriptor in non-blocking mode: usually, the fcntl system call or similar is used to set the O_NONBLOCK flag.

Example of setting non-blocking mode in C:

#include <fcntl.h>

int flags = fcntl(fd, F_GETFL, 0);
fcntl(fd, F_SETFL, flags | O_NONBLOCK);

Thus, when working with non-blocking descriptors, it is important to handle situations where the operation cannot be completed immediately and to use asynchronous waiting mechanisms.