added sock20

TMP/Practice/04.10/shmat/svshm_string_read.c

@@ -2,59 +2,61 @@
 #include <stdlib.h>
 #include <sys/ipc.h>
 #include <sys/sem.h>
-#include <unistd.h>
+#include <sys/shm.h>
 
-static void
-usage(const char *pname)
+#include "svshm_string.h"
+
+int main(void)
 {
-    fprintf(stderr, "Usage: %s [-cx] pathname proj-id num-sems\n",
-            pname);
-    fprintf(stderr, "    -c           Use IPC_CREAT flag\n");
-    fprintf(stderr, "    -x           Use IPC_EXCL flag\n");
-    exit(EXIT_FAILURE);
-}
+    int semid, shmid;
+    char *addr;
+    union semun arg, dummy;
+    struct sembuf sop;
 
-int main(int argc, char *argv[])
-{
-    int semid, nsems, flags, opt;
-    key_t key;
+    /* Create shared memory and semaphore set containing one
+       semaphore. */
 
-    flags = 0;
-    while ((opt = getopt(argc, argv, "cx")) != -1)
-    {
-        switch (opt)
-        {
-        case 'c':
-            flags |= IPC_CREAT;
-            break;
-        case 'x':
-            flags |= IPC_EXCL;
-            break;
-        default:
-            usage(argv[0]);
-        }
-    }
+    shmid = shmget(IPC_PRIVATE, MEM_SIZE, IPC_CREAT | 0600);
+    if (shmid == -1)
+        errExit("shmget");
 
-    if (argc != optind + 3)
-        usage(argv[0]);
-
-    key = ftok(argv[optind], argv[optind + 1][0]);
-    if (key == -1)
-    {
-        perror("ftok");
-        exit(EXIT_FAILURE);
-    }
-
-    nsems = atoi(argv[optind + 2]);
-
-    semid = semget(key, nsems, flags | 0600);
+    semid = semget(IPC_PRIVATE, 1, IPC_CREAT | 0600);
     if (semid == -1)
-    {
-        perror("semget");
-        exit(EXIT_FAILURE);
-    }
+        errExit("semget");
 
-    printf("ID = %d\n", semid);
+    /* Attach shared memory into our address space. */
+
+    addr = shmat(shmid, NULL, SHM_RDONLY);
+    if (addr == (void *)-1)
+        errExit("shmat");
+
+    /* Initialize semaphore 0 in set with value 1. */
+
+    arg.val = 1;
+    if (semctl(semid, 0, SETVAL, arg) == -1)
+        errExit("semctl");
+
+    printf("shmid = %d; semid = %d\n", shmid, semid);
+
+    /* Wait for semaphore value to become 0. */
+
+    sop.sem_num = 0;
+    sop.sem_op = 0;
+    sop.sem_flg = 0;
+
+    if (semop(semid, &sop, 1) == -1)
+        errExit("semop");
+
+    /* Print the string from shared memory. */
+
+    printf("%s\n", addr);
+
+    /* Remove shared memory and semaphore set. */
+
+    if (shmctl(shmid, IPC_RMID, NULL) == -1)
+        errExit("shmctl");
+    if (semctl(semid, 0, IPC_RMID, dummy) == -1)
+        errExit("semctl");
 
     exit(EXIT_SUCCESS);
 }