Advanced Programming in the UNIX® Environment

ptg10805159

934 Solutions to Selected Exercises Appendix C

#include <poll.h>

void

sleep_us(unsigned int nusecs)

{

struct pollfd dummy;

int timeout;

if ((timeout = nusecs / 1000) <= 0)

timeout = 1;

poll(&dummy, 0, timeout);

}

Figure C.17 Implementation ofsleep_ususingpoll

As the BSD usleep( 3 ) manual page states, usleep uses the nanosleep

function, which doesn’t interferewith timers set by the calling process.

14.6 No. What we would like to do is haveTELL_WAITcreate a temporary file and

use 1 byte for the parent’s lock and 1 byte for the child’s lock. WAIT_CHILD

would have the parent wait to obtain a lock on the child’s byte, and

TELL_PARENTwould have the child release the lock on the child’s byte. The

problem, however,isthat callingforkreleases all the locks in the child, so the

child can’t start offwith any locks of its own.

14.7 Asolution is shown in FigureC.18.

#include "apue.h"

#include <fcntl.h>

int

main(void)

{

int i, n;

int fd[2];

if (pipe(fd) < 0)

err_sys("pipe error");

set_fl(fd[1], O_NONBLOCK);

/* write 1 byte at a time until pipe is full */

for (n = 0; ; n++) {

if ((i = write(fd[1], "a", 1)) != 1) {

printf("write ret %d, ", i);

break;

}

}

printf("pipe capacity = %d\n", n);

exit(0);

}

Figure C.18 Calculation of pipe capacity using nonblocking writes