pSOSystem System Calls - Read

pNA+ System Calls select
Usage
timeout Specifies a timeout option. If the fields in timeout are set to 0,
select() returns immediately. If the timeout is a null pointer,
select() blocks until a descriptor is selectable. The structure
timeval is defined in the file and has the following format:
Macros
The status of a socket descriptor in a select mask can be tested with the
FD_ISSET(s, &mask) macro, which returns a non-zero value if s is a member of the
set mask, and 0 if it is not.
In addition, the macros FD_SET(s, &mask) and FD_CLEAR(s, &mask) are provided for
adding and removing socket descriptors to and from a set. s is the socket descriptor,
and mask points to a bit mask data structure. The macro FD_ZERO(&mask) is
provided to clear the set and should be used before the set is used.
These macros are defined in the file .
Example
struct timeval {
long tv_sec; /* number of seconds */
long tv_usec; /* number of microseconds */
The following example shows how to use select() to determine if two sockets have
available data:
fd_set read_mask;
struct timeval wait;
for (;;)
{
wait.tv_sec = 1; /* wait for 1 second */
wait.tv_usec = 0;
FD_ZERO (&read_mask);
FD_SET (s1, &read_mask);
FD_SET (s2, &read_mask);
nb = select (FD_SETSIZE, &read_mask, (fd_set *) 0,
(fd_set *) 0, &wait);
if (nb