From 0c9d712a77bbede4808142944776d35f502bffa7 Mon Sep 17 00:00:00 2001
From: Michael Stapelberg <michael@stapelberg.de>
Date: Mon, 6 Dec 2010 19:55:19 +0100
Subject: IPC implementiert
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Hat noch einen Bug, sollte aber als Beispiel für die anderen Aufgaben gut genug
sein.
---
 aufgabe4/queue.c | 138 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 138 insertions(+)
 create mode 100644 aufgabe4/queue.c

(limited to 'aufgabe4/queue.c')

diff --git a/aufgabe4/queue.c b/aufgabe4/queue.c
new file mode 100644
index 0000000..62a888c
--- /dev/null
+++ b/aufgabe4/queue.c
@@ -0,0 +1,138 @@
+/*
+ * 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 int fd;
+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 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);
+    }
+
+    shmheader = (struct queueheader*)shm;
+    shmdata = (struct msg*)(shm + sizeof(struct queueheader));
+
+    shmheader->cur = 0;
+    shmdata->dir = D_INVALID;
+
+    /* 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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