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Semaphore/inc/main.h

@@ -0,0 +1,7 @@
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/ipc.h>
+#include <sys/sem.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>

Semaphore/src/main.c

@@ -0,0 +1,81 @@
+#include "main.h"
+
+#define KEY 0x1111
+
+union semun {
+    int value;
+    struct semid_ds *buf;
+    unsigned short *arr;
+};
+
+struct sembuf a = {0, -1, SEM_UNDO};
+struct sembuf b = {0, +1, SEM_UNDO};
+
+int main(void)
+{
+    int id = semget(KEY, 1, 0666 | IPC_CREAT);
+    if (id < 0) {
+        perror("semget\n");
+        exit(0);
+    }
+    union semun su;
+    su.value = 1;
+
+    if(semctl(id, 0, SETVAL, su) < 0) {
+        perror("semctl error");
+        exit(0);
+    }
+
+    int pid;
+
+    pid = fork();
+    srand(pid);
+
+    if (pid < 0) {
+        perror("fork error\n");
+        exit(0);
+    } else if (pid) {
+        char *se = "abc";
+        int l = strlen(se);
+
+        for (int i = 0; i < l; i++) {
+            if (semop(id, &a, 1) < 0) {
+                perror("semop error with a\n");
+                exit(0);
+            } 
+            putchar(se[i]);
+            fflush(stdout);
+            sleep(1);
+            putchar(se[i]);
+            fflush(stdout);
+            if (semop(id, &b, 1) < 0) {
+                perror("semop error with b\n");
+                exit(0);
+            }
+
+            sleep(1);
+        }
+    } else {
+        char *se = "abc";
+        int l = strlen(se);
+
+        for (int i = 0; i < l; i++) {
+            if (semop(id, &a, 1) < 0) {
+                perror("semop error with a\n");
+                exit(0);
+            } 
+            putchar(se[i]);
+            fflush(stdout);
+            sleep(1);
+            putchar(se[i]);
+            fflush(stdout);
+            if (semop(id, &b, 1) < 0) {
+                perror("semop error with b\n");
+                exit(0);
+            }
+
+            sleep(1);
+        }       
+    }
+    return 0;
+}