Asynchronous Socket I/O

Asynchronous communication between processes is required in applications that simultaneously handle multiple requests. Asynchronous sockets must be of the SOCK_STREAM type. To make a socket asynchronous, you issue a fcntl(2) call, as shown in the following example.

Example 8–12 Making a Socket Asynchronous

#include <fcntl.h>
#include <sys/file.h>
...
int fileflags;
int s;
...
s = socket(AF_INET6, SOCK_STREAM, 0);
...
if (fileflags = fcntl(s, F_GETFL ) == -1)
    perror("fcntl F_GETFL");
    exit(1);
}
if (fcntl(s, F_SETFL, fileflags | FNDELAY | FASYNC) == -1)
    perror("fcntl F_SETFL, FNDELAY | FASYNC");
    exit(1);
}

After sockets are initialized, connected, and made nonblocking and asynchronous, communication is similar to reading and writing a file asynchronously. Initiate a data transfer by using send(3SOCKET), write(2), recv(3SOCKET), or read(2). A signal-driven I/O routine completes a data transfer, as described in the next section.