Advanced Programming in the UNIX® Environment

ptg10805159

Appendix C Chapter 14 Solutions 933

the definition of thefd_settype with a separate symbol. We need to define

this, too.

For example, on FreeBSD 8.0, we need to define _SYS_SELECT_H_ to

prevent the inclusion of<sys/select.h>and we need to define_FD_SET

to prevent the inclusion of the definition for thefd_setdata type.

2. Sometimes, for compatibility with older applications, <sys/types.h>
   defines the size of thefd_set, so we need to include it first, then undefine
   FD_SETSIZE.Note that some systems use__FD_SETSIZEinstead.


3. Weneed to redefineFD_SETSIZE(or__FD_SETSIZE)tothe maximum file
   descriptor number we want to be able to use withselect.


4. Weneed to undefine the symbols we defined in step 1.


5. Finally, we can include<sys/select.h>.

Before we run the program, we need to configurethe system to allow us to open

as many file descriptors as we might need so that we can actually make use of

FD_SETSIZEfile descriptors.

14.4 The following table lists the functions that do similar things.

FD_ZERO sigemptyset

FD_SET sigaddset

FD_CLR sigdelset

FD_ISSET sigismember

There is not anFD_xxxfunction that corresponds tosigfillset.With signal

sets, the pointer to the set is always the first argument, and the signal number is

the second argument. With descriptor sets, the descriptor number is the first

argument, and the pointer to the set is the next argument.

14.5 FigureC.16 shows an implementation usingselect.

#include "apue.h"

#include <sys/select.h>

void

sleep_us(unsigned int nusecs)

{

struct timeval tval;

tval.tv_sec = nusecs / 1000000;

tval.tv_usec = nusecs % 1000000;

select(0, NULL, NULL, NULL, &tval);

}

Figure C.16 Implementation ofsleep_ususingselect

FigureC.17 shows an implementation usingpoll.