更新读书记录 增加进程同步demo

Author: HiganFish

14. 进程同步demo/main.cpp

@@ -0,0 +1,90 @@
+#include <sys/sem.h>
+#include <sys/types.h>
+#include <cstdlib>
+#include <unistd.h>
+#include <cstdio>
+
+union semun
+{
+    int              val;    /* Value for SETVAL */
+    struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET */
+    unsigned short  *array;  /* Array for GETALL, SETALL */
+    struct seminfo  *__buf;  /* Buffer for IPC_INFO(Linux-specific) */
+};
+
+bool P(int sem_id)
+{
+    struct sembuf sem_b;
+    sem_b.sem_num = 0;
+    sem_b.sem_op = -1; // P
+    sem_b.sem_flg = SEM_UNDO;
+    return semop(sem_id, &sem_b, 1) != -1;
+}
+
+int V(int sem_id)
+{
+    struct sembuf sem_b;
+    sem_b.sem_num = 0;
+    sem_b.sem_op = 1; // V
+    sem_b.sem_flg = SEM_UNDO;
+    return semop(sem_id, &sem_b, 1) != -1;
+}
+
+int main(int argc, char *argv[])
+{
+    char message = 'x';
+
+    int sem_id = semget((key_t) 1234, 1, 0666 | IPC_CREAT);
+
+    // 初次调用程序初始化信号量
+    if (argc > 1)
+    {
+        // 初始化信号量
+        union semun sem_union;
+        sem_union.val = 1;
+
+        if (semctl(sem_id, 0, SETVAL, sem_union) == -1)
+        {
+            exit(0);
+        }
+        message = argv[1][0];
+        sleep(2);
+    }
+
+    for (int i = 0; i < 10; ++i)
+    {
+        if (!P(sem_id))
+        {
+            exit(EXIT_FAILURE);
+        }
+        // 打印自己的特有message
+        printf("%c", message);
+        fflush(stdout);
+
+        sleep(rand() % 3);
+
+        printf("%c", message);
+        fflush(stdout);
+
+        if (!V(sem_id))
+        {
+            exit(EXIT_FAILURE);
+        }
+    }
+
+    sleep(2);
+    printf("\n%d - finished\n", getpid());
+
+    // 初次调用完删除信号量
+    if (argc > 1)
+    {
+        sleep(3);
+        // 删除信号量
+        union semun sem_union{};
+        if (semctl(sem_id, 0, IPC_RMID, sem_union) == -1)
+        {
+            exit(EXIT_FAILURE);
+        }
+    }
+    exit(EXIT_SUCCESS);
+}