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/*
* vim:ts=4:sw=4:expandtab
*
* © 2010 Michael Stapelberg
*
*/
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdbool.h>
#include <string.h>
#include <semaphore.h>
#include <errno.h>
#include "queue.h"
static const int queue_size = sizeof(struct queueheader) + (sizeof(struct msg) * 255);
static uint8_t *shm;
static struct queueheader *shmheader;
static struct msg *shmdata;
/*
* Sperrt den Semaphor: Nun kann im Shared Memory-Bereich geschrieben werden.
*
*/
static void lock() {
while (1) {
if (sem_wait(&(shmheader->sem)) == -1) {
if (errno == EINTR)
continue;
perror("sem_wait");
exit(EXIT_FAILURE);
}
break;
}
}
/*
* Entsperrt den Semaphor.
*
*/
static void unlock() {
sem_post(&(shmheader->sem));
}
/*
* Initialisiert das Shared Memory-Segment, bildet es in den Speicher ab und
* initialisiert den Semaphor.
*
*/
void queue_init() {
int c;
int fd;
int flags = O_RDWR | O_CREAT | O_TRUNC;
if ((fd = shm_open("/bts-sem", flags, S_IREAD | S_IWRITE)) == -1) {
perror("shm_open");
exit(EXIT_FAILURE);
}
ftruncate(fd, queue_size);
if ((shm = mmap(0, queue_size, (PROT_READ | PROT_WRITE),
MAP_SHARED, fd, 0)) == MAP_FAILED) {
perror("mmap");
exit(EXIT_FAILURE);
}
close(fd);
shmheader = (struct queueheader*)shm;
shmdata = (struct msg*)(shm + sizeof(struct queueheader));
/* Speicher mit 0 initialisieren */
memset(shmheader, 0, sizeof(struct queueheader));
struct msg *curmsg = shmdata;
for (c = 0; c < 255; c++) {
curmsg->dir = D_INVALID;
curmsg++;
}
/* Semaphor initialisieren */
if (sem_init(&(shmheader->sem), 1, 1) != 0) {
perror("sem_init");
exit(EXIT_FAILURE);
}
}
/*
* Hängt den übergebenen Wert in die Queue.
*
*/
struct msg *queue_write(uint8_t dir, uint8_t data) {
struct msg msg;
msg.dir = dir;
msg.data = data;
uint8_t next;
if (shmheader->cur == 255)
next = 0;
else next = shmheader->cur + 1;
lock();
struct msg *curmsg = shmdata + (shmheader->cur * sizeof(struct msg));
struct msg *nextmsg = shmdata + (next * sizeof(struct msg));
memcpy(nextmsg, &msg, sizeof(struct msg));
if (curmsg->dir == D_INVALID)
shmheader->cur = next;
unlock();
return nextmsg;
}
/*
* Gibt die Quelle der derzeit zu verarbeitenden Nachricht zurück.
*
*/
uint8_t queue_get_dir() {
struct msg *curmsg = shmdata + (shmheader->cur * sizeof(struct msg));
return curmsg->dir;
}
/*
* Gibt den Wert der derzeit zu verarbeitenden Nachricht zurück und invalidiert
* diese.
*
*/
uint8_t queue_get_data() {
uint8_t data;
struct msg *curmsg = shmdata + (shmheader->cur * sizeof(struct msg));
data = curmsg->data;
lock();
curmsg->dir = D_INVALID;
if (shmheader->cur == 255)
shmheader->cur = 0;
else shmheader->cur++;
unlock();
return data;
}
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