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#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include "noeintr.h"
#include "warnp.h"
#include "ipc_sync.h"
/* Convention for read/write ends of a pipe. */
#define R 0
#define W 1
struct ipc_sync {
int fd[2];
};
/* Read and discard one byte from ${fd}, looping upon EINTR. */
static inline int
readbyte(int fd)
{
char dummy;
char done = 0;
/* Loop until done. */
do {
switch (read(fd, &dummy, 1)) {
case -1:
/* Anything other than EINTR is bad. */
if (errno != EINTR) {
warnp("read");
goto err0;
}
/* Otherwise, loop and read again. */
break;
case 0:
warn0("Unexpected EOF in pipe");
goto err0;
case 1:
/* Expected value; quit the loop. */
done = 1;
}
} while (!done);
/* Success! */
return (0);
err0:
/* Failure! */
return (-1);
}
/* Write one byte from ${fd}, looping upon EINTR. */
static inline int
writebyte(int fd)
{
char dummy = 0;
/* Do the write. */
if (noeintr_write(fd, &dummy, 1) == -1) {
warnp("write");
goto err0;
}
/* Success! */
return (0);
err0:
/* Failure! */
return (-1);
}
/* close(), but looping upon EINTR. */
static inline int
ipc_sync_close(int fd)
{
/* Loop until closed. */
while (close(fd)) {
if (errno == EINTR)
continue;
warnp("close");
goto err0;
}
/* Success! */
return (0);
err0:
/* Failure! */
return (-1);
}
/* Close the unneeded read or write end of the pipe. */
static int
ipc_sync_prep(struct ipc_sync * IS, int num)
{
/* Bail if there's nothing to do. */
if (IS->fd[num] == -1)
return (0);
/*
* Close the indicated end of pipe so that if the other process dies,
* we will notice the pipe being reset.
*/
if (ipc_sync_close(IS->fd[num]))
goto err0;
IS->fd[num] = -1;
/* Success! */
return (0);
err0:
/* Failure! */
return (-1);
}
/**
* ipc_sync_init(void):
* Initialize an inter-process synchronization barrier. This must be called
* before forking.
*/
struct ipc_sync *
ipc_sync_init(void)
{
struct ipc_sync * IS;
/* Allocate the cookie. */
if ((IS = malloc(sizeof(struct ipc_sync))) == NULL) {
warnp("malloc");
goto err0;
}
/* Set up synchronization. */
if (pipe(IS->fd)) {
warnp("pipe");
goto err1;
}
/* Success! */
return (IS);
err1:
free(IS);
err0:
/* Failure! */
return (NULL);
}
/**
* ipc_sync_wait(IS):
* Block until ipc_sync_signal() has been called with ${IS}.
*/
int
ipc_sync_wait(struct ipc_sync * IS)
{
/* Ensure that we've closed the write end. */
if (ipc_sync_prep(IS, W))
return (-1);
/* Read and discard a byte from the read end of the pipe. */
return (readbyte(IS->fd[R]));
}
/**
* ipc_sync_signal(IS):
* Indicate that ${IS} should no longer block.
*/
int
ipc_sync_signal(struct ipc_sync * IS)
{
/* Ensure that we've closed the read end. */
if (ipc_sync_prep(IS, R))
return (-1);
/* Write a byte to the write end of the pipe. */
return (writebyte(IS->fd[W]));
}
/**
* ipc_sync_wait_prep(IS):
* Perform any operation(s) that would speed up an upcoming call to
* ipc_sync_wait(). Calling this function is optional.
*/
int
ipc_sync_wait_prep(struct ipc_sync * IS)
{
/* Ensure that we've closed the write end. */
return (ipc_sync_prep(IS, W));
}
/**
* ipc_sync_signal_prep(IS):
* Perform any operation(s) that would speed up an upcoming call to
* ipc_sync_signal(). Calling this function is optional.
*/
int
ipc_sync_signal_prep(struct ipc_sync * IS)
{
/* Ensure that we've closed the read end. */
return (ipc_sync_prep(IS, R));
}
/**
* ipc_sync_done(IS):
* Free resources associated with ${IS}.
*/
int
ipc_sync_done(struct ipc_sync * IS)
{
/* Close any open file descriptors. */
if ((IS->fd[W] != -1) && ipc_sync_close(IS->fd[W]))
goto err1;
if ((IS->fd[R] != -1) && ipc_sync_close(IS->fd[R]))
goto err2;
/* Clean up. */
free(IS);
/* Success! */
return (0);
err2:
if (IS->fd[R] != -1)
ipc_sync_close(IS->fd[R]);
err1:
free(IS);
/* Failure! */
return (-1);
}
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